Neuromuscular Fatigue and Tibiofemoral Joint Biomechanics When Transitioning From Non–Weight Bearing to Weight Bearing

Context:Fatigue is suggested to be a risk factor for anterior cruciate ligament injury. Fatiguing exercise can affect neuromuscular control and laxity of the knee joint, which may render the knee less able to resist externally applied loads. Few authors have examined the effects of fatiguing exercise on knee biomechanics during the in vivo transition of the knee from non–weight bearing to weight bearing, the time when anterior cruciate ligament injury likely occurs.Objective:To investigate the effect of fatiguing exercise on tibiofemoral joint biomechanics during the transition from non–weight bearing to early weight bearing.Design:Cross-sectional study.Setting:Research laboratory.Intervention(s):Participants were tested before (preexercise) and after (postexercise) a protocol consisting of repeated leg presses (15 repetitions from 10°–40° of knee flexion, 10 seconds'' rest) against a 60% body-weight load until they were unable to complete a full bout of repetitions.Results:The axial compressive force (351.8 ± 44.3 N versus 374.0 ± 47.9 N; P = .018), knee-flexion excursion (8.0° ± 4.0° versus 10.2° ± 3.7°; P = .046), and anterior tibial translation (6.7 ± 1.7 mm versus 8.2 ± 1.9 mm; P < .001) increased from preexercise to postexercise. No significant correlations were noted.Conclusions:Neuromuscular fatigue may impair initial knee-joint stabilization during weight acceptance, leading to greater accessory motion at the knee and the potential for greater anterior cruciate ligament loading.Key Words: knee, anterior cruciate ligament, axial loading

Key Points

• After closed chain exercise, participants demonstrated an increase in anterior tibial translation during simulated lower extremity weight acceptance.
• Observed alterations of knee biomechanics in a fatigued state may suggest increased anterior cruciate ligament strain during the latter part of the competition.

The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments in the knee.^1–4 Injuries to the ACL frequently result from noncontact mechanisms, occurring when the knee is near full extension at the time of foot strike during activities such as landing, cutting, and deceleration-type maneuvers.⁵ Neuromuscular fatigue has been defined as any exercise-induced loss in the ability to produce force with a muscle or muscle group, involving processes at all levels of the motor pathway between the brain and the muscle.^6–8 Furthermore, fatigue has been suggested as a contributing risk factor for noncontact ACL injury^9–14 because the risk of noncontact knee injuries appears to increase later in games.^15,16 Specifically, prolonged exercise, which contributes to the delayed activation of muscles agonistic to the ACL,^13,17 has been suggested to increase risk of knee injury.¹³The quadriceps and hamstrings play a critical role in providing dynamic stability of the knee joint during sports activities,¹⁸ so various lower extremity fatigue protocols have been used to decrease the force-producing capabilities of these muscles.^10,19,20 Commonly, fatigue has been induced using isokinetic exercise protocols.^12,14,21,22 However, the true nature of muscle function and its effect on functional knee-joint biomechanics during sporting activity is likely difficult to assess from isolated forms of isometric, concentric, or eccentric contractions. Exercise that results in complete volitional exhaustion of a single muscle or muscle group rarely occurs during functional activity. Therefore, fatigue protocols that involve total lower extremity actions incorporating submaximal stretch-shortening cycles^23,24 may better mimic the type of muscular fatigue associated with prolonged weight-bearing activity.A number of authors^23,25,26 have examined the effect of lower extremity muscle fatigue on knee-joint biomechanics during jumping and landing activities. These results suggest that, depending on the fatigue protocol and task used, knee-flexion excursion (KF_EXC) may be either decreased or increased postexercise, thus modulating joint stiffness.^25,27 These changes in KF_EXC appear to primarily depend on the peak knee flexion obtained,^11,27 given that little to no change in the initial knee-flexion landing angle has been reported at ground contact in response to fatiguing exercise.^9,20 Moran et al²⁸ examined the effect of an incremental treadmill protocol and reported that exercise-induced alterations in tibial peak-impact acceleration were not attributed to changes in the knee angles at foot contact during a drop jump. This suggests that fatiguing exercise does not alter the initial knee-position angle at ground contact, but it may have a profound effect on knee-joint biomechanics during the weight-acceptance phase of landing. Because ACL injuries typically occur near the time of foot strike^1,4 with the knee in shallow flexion (average, 23° of initial knee flexion),²⁹ understanding the effect of fatiguing exercise on knee-joint biomechanics during this early weight-acceptance phase may lend further insight into the role of fatigue in ACL injury mechanisms.As the knee transitions from non–weight bearing (NWB) to weight bearing (WB), the natural anterior translation of the tibia (ATT) relative to the femur at low knee-flexion angles (eg, 15°–30°)^30,31 is restrained by the ACL.³¹ Greater axial loads^30,32,33 and slowing of the quadriceps and hamstrings onset times in response to an anterior tibial load may contribute to increased ATT¹⁴ at shallow knee-flexion angles; hence, fatigue may compromise the biomechanics of the tibiofemoral joint during weight acceptance, thereby modifying the strain placed upon the ACL with continued loading and subsequent maneuvers (eg, plant and cut). This may be particularly problematic in landing situations where KF_EXC decreases in response to fatiguing exercise.^9,25,34 Although decreased KF_EXC may represent a compensatory strategy to prevent collapse of the body due to fatigue of the quadriceps muscles,^10,34 the reduced KF_EXC may increase axial loads at the knee joint, and these greater axial loads may increase the amount of ATT.³⁵The purpose of our study was to investigate the effects of a lower extremity exercise protocol on tibiofemoral-joint biomechanics as the knee transitioned from NWB to WB in vivo. Based on previous fatigue studies of submaximal total lower extremity actions,^9,25 our expectation was that fatiguing exercise would decrease KF_EXC, increase axial compressive force (ACF), and subsequently increase ATT during transition from NWB to WB.     

Strength-Training Protocols to Improve Deficits in Participants With Chronic Ankle Instability: A Randomized Controlled Trial

Context:Although lateral ankle sprains are common in athletes and can lead to chronic ankle instability (CAI), strength-training rehabilitation protocols may improve the deficits often associated with CAI.Objective:To determine whether strength-training protocols affect strength, dynamic balance, functional performance, and perceived instability in individuals with CAI.Design:Randomized controlled trial.Setting:Athletic training research laboratory.Intervention(s):Both rehabilitation groups completed their protocols 3 times/wk for 6 weeks. The control group did not attend rehabilitation sessions.Results:The resistance-band protocol group improved in strength (dorsiflexion, inversion, and eversion) and on the visual analog scale (P < .05); the proprioceptive neuromuscular facilitation group improved in strength (inversion and eversion) and on the visual analog scale (P < .05) as well. No improvements were seen in the triple-crossover hop or the Y-Balance tests for either intervention group or in the control group for any dependent variable (P > .05).Conclusions:Although the resistance-band protocol is common in rehabilitation, the proprioceptive neuromuscular facilitation strength protocol is also an effective treatment to improve strength in individuals with CAI. Both protocols showed clinical benefits in strength and perceived instability. To improve functional outcomes, clinicians should consider using additional multiplanar and multijoint exercises.Key Words: functional ankle instability, functional performance, rehabilitation, Star Excursion Balance Test

Key Points

• Proprioceptive neuromuscular facilitation is an alternate strength-training protocol that was effective in enhancing ankle strength in those with chronic ankle instability.
• Neither the resistance-band protocol nor the proprioceptive neuromuscular facilitation protocol improved dynamic balance or functional performance in individuals with chronic ankle instability.

Lateral ankle sprains are very common in athletes¹ and account for 80% of injuries to the ankle.² These injuries can cause damage to the ligaments, muscles, nerves, and mechanoreceptors that cross the lateral ankle.³ Repetitive occurrences of lateral ankle sprains can lead to chronic ankle instability (CAI),^4–6 which is characterized by a subjective feeling of recurrent instability, repeated episodes of giving way, weakness during physical activity, and self-reported disability.^5,7,8 Patients with CAI often exhibit deficits in functional performance,^9–13 proprioception,^5,14–16 and strength.^4,5,16,17Because muscle weakness is associated with CAI, strength training is an essential part of the rehabilitation protocol¹⁷ to reduce the residual symptoms and, we hope, to prevent further episodes of instability from occurring. Strength training improves the physical conditioning of participants with ankle instability.^16,18–25 Strength training is thought to promote muscular gains during the first 3 to 5 weeks because it enhances neural factors.²⁶ Therefore, strength training may improve proprioception and balance deficits.^18,24,25 Conflicting findings exist in the current literature^14,23; thus, the relationship between strength training and other factors, such as balance, proprioception, or functional performance, requires further investigation.Most authors^{18,20,21,23,25} who have investigated the effect of strength training in people with CAI have used resistive-tubing exercises 3 times/wk for 4 weeks²⁰ to 6 weeks.^18,21,23,25 Other rehabilitation protocols have involved manual resistance at the ankle²² and isokinetic strength training.²⁴ Some researchers^{18,21,23–25} focused on strength-training protocols alone, whereas others^{19,20,22,27,28} have used multicomponent protocols that included balance exercises. Improvements in strength,^18,24,25 static balance,²⁴ joint position sense,¹⁸ and functional performance tests²⁴ were reported.Proprioceptive neuromuscular facilitation (PNF) is another form of progressive strength training that emphasizes multiplanar motion.²⁹ The goal of PNF techniques is to promote functional movement through facilitation (strengthening) and inhibition (relaxation) of muscle groups.³⁰ Although it is used more often at the shoulder, hip, and knee joints, PNF can also be used at the ankle.³¹ Two studies^32,33 compared the differences between common lower extremity strength-training programs and PNF strength-training patterns. The PNF pattern for both studies used the sequential movements of toe flexion, ankle plantar flexion and eversion, knee and hip extension, abduction, and internal rotation in the lower extremity. The PNF strength patterns were as effective as isokinetic training³² and weight training³³ in improving knee strength and functional performance. Based on the deficits seen in patients with CAI, PNF may be a beneficial treatment approach. Because PNF patterns are similar to functional movement patterns,²⁹ PNF strength techniques may also improve dynamic balance and functional performance.Although a multicomponent rehabilitation protocol is often used after an injury, examining 1 component, such as strength, in a controlled research setting will allow us to determine the effectiveness of a single approach. If strength training alone can improve multiple deficits seen in patients with CAI, it could save time for both clinician and patient. A resistance-band protocol has already been established as an effective strength-training protocol in improving some deficits in people with CAI.^18,24,25 Therefore, the purpose of our study was to compare the effects of resistance-band (RBP) and PNF protocols on strength, dynamic balance, functional performance, and perceived instability in individuals with CAI.     

Anticipatory Effects on Lower Extremity Neuromechanics During a Cutting Task

Context

 Continued research into the mechanism of noncontact anterior cruciate ligament injury helps to improve clinical interventions and injury-prevention strategies. A better understanding of the effects of anticipation on landing neuromechanics may benefit training interventions.

Objective

 To determine the effects of anticipation on lower extremity neuromechanics during a single-legged land-and-cut task.

Design

 Controlled laboratory study.

Setting

 University biomechanics laboratory.

Participants

 Eighteen female National Collegiate Athletic Association Division I collegiate soccer players (age = 19.7 ± 0.8 years, height = 167.3 ± 6.0 cm, mass = 66.1 ± 2.1 kg).

Intervention(s)

 Participants performed a single-legged land-and-cut task under anticipated and unanticipated conditions.

Main Outcome Measure(s)

 Three-dimensional initial contact angles, peak joint angles, and peak internal joint moments and peak vertical ground reaction forces and sagittal-plane energy absorption of the 3 lower extremity joints; muscle activation of selected hip- and knee-joint muscles.

Results

 Unanticipated cuts resulted in less knee flexion at initial contact and greater ankle toe-in displacement. Unanticipated cuts were also characterized by greater internal hip-abductor and external-rotator moments and smaller internal knee-extensor and external-rotator moments. Muscle-activation profiles during unanticipated cuts were associated with greater activation of the gluteus maximus during the precontact and landing phases.

Conclusions

 Performing a cutting task under unanticipated conditions changed lower extremity neuromechanics compared with anticipated conditions. Most of the observed changes in lower extremity neuromechanics indicated the adoption of a hip-focused strategy during the unanticipated condition.Key Words: anticipation, anterior cruciate ligament, biomechanics

Key Points

• Participants demonstrated that the hip joint played a substantially greater role as part of the neuromechanical landing strategy during the unanticipated condition.
• The unanticipated condition was characterized by only a few changes in landing mechanics consistent with greater anterior cruciate ligament loading.

Noncontact anterior cruciate ligament (ACL) injuries are a common occurrence in sport.¹ When compared with their male counterparts, females are at a 3.5 to 4 times higher risk of sustaining an injury to the ACL.^2–4 Among ACL injuries in females, the most frequent mechanism of injury occurs in the absence of contact. On average, 70% to 80% of all noncontact ACL tears involve rapid deceleration during a landing or cutting maneuver.^2,5 To develop clinical interventions that aim to prevent injuries, research efforts have been directed at determining how biomechanical and neuromuscular risk factors manifest within the ACL injury mechanism.^6–16 Most authors^9,14,17,18 who investigated these risk factors and their role in the ACL injury mechanism focused on kinetic and kinematic variables measured during landing and cutting tasks. These results suggest that deleterious knee kinetics are characterized by greater external-flexion, abduction, and internal-rotation moments.^9,14,17,18 In addition, other kinematic factors, such as smaller hip and knee sagittal-plane angles along with greater frontal-plane angles and ranges of motion, have been identified as components of an at-risk movement pattern.^{7,11,14,17,18} This movement pattern has also been evident during direct observations of ACL injuries using video analysis of in-game footage and as part of a prospective investigation of ACL injury risk.^6,19,20Many of the biomechanical studies^{8,11,13,21,22} that investigated landing mechanics and movement patterns used experimental models in which participants completed preplanned movement tasks (eg, cutting or landing or both) with an anticipated or known direction of movement. However, executing movement tasks under such conditions may not accurately represent the dynamic and evolving environment in which athletic activities occur. Researchers, therefore, try to mimic the uncertainty of these conditions by having participants perform tasks without knowing which direction to move in before they actually initiate the movement.^{7,9,12,14,15,17,18,23,24} It is interesting, however, that direct comparisons between lower extremity mechanics performed under anticipated and unanticipated conditions have not been conducted as often as comparisons between groups that performed only unanticipated conditions. Yet, analyzing biomechanical and neuromuscular variables under either condition alone may not provide sufficient information about the neuromechanical strategies that athletes adopt when faced with situations that more closely resemble the dynamic athletic environment. That may ultimately limit the insight available to develop appropriate training programs to prevent injury.The few researchers^12,14,15 who directly compared anticipated and unanticipated conditions generally indicated that lower extremity mechanics were exacerbated when movement tasks were performed under unanticipated conditions. These results, however, primarily described differences in knee-joint biomechanics (ie, kinematics and kinetics) between movement tasks performed under anticipated and unanticipated conditions. Much less is known about the effects of anticipation on the biomechanics of more proximal joints (ie, the hip) or the underlying neuromuscular-control strategies that athletes adopt to cope with the demands presented by the unanticipated conditions.^8,25 Collecting electromyographic (EMG) data during dynamic movement tasks generally enhances the interpretation of traditional kinematic and kinetic data and, in the case of unanticipated movement conditions, would provide better global insight into the neuromechanical strategies that athletes adopt under suboptimal conditions for planning and executing task-appropriate movement patterns. Given the importance of hip-joint function in controlling upper body momentum and influencing lower body mechanics during landing,^10,21,26,27 the lack of knowledge about proximal biomechanics and muscle- activation patterns (eg, the gluteus maximus and medius) during unanticipated landing and cutting tasks could possibly limit insight into how neuromechanical strategies affect the ACL injury mechanism.The purpose of our study was to analyze the effects of anticipation on lower extremity neuromechanics during a single-legged land-and-cut task. Specific emphasis was placed on muscle-activation patterns, in addition to kinematic and kinetic analyses, to obtain a more complete understanding of the neuromechanical strategies during landing in relation to the ACL injury mechanism. We hypothesized that landing under unanticipated conditions would be characterized by more deleterious joint kinematics, kinetics, and muscle-activation patterns in regard to the risk of noncontact ACL injury.     

Lower Extremity Fatigue,Sex, and Landing Performance in a Population With Recurrent Low Back Pain

Context:Low back pain and lower extremity injuries affect athletes of all ages. Previous authors have linked a history of low back pain with lower extremity injuries. Fatigue is a risk factor for lower extremity injuries, some of which are known to affect female athletes more often than their male counterparts.Objective:To determine the effects of lower extremity fatigue and sex on knee mechanics, neuromuscular control, and ground reaction force during landing in people with recurrent low back pain (LBP).Design:Cross-sectional study.Setting:A clinical biomechanics laboratory.Intervention(s):Fatigue was induced using a submaximal free-weight squat protocol with 15% body weight until task failure was achieved.Results:Fatigue altered landing mechanics, with differences in landing performance between sexes. Women tended to have greater knee-flexion angle at initial contact, greater maximum knee internal-rotation angle, greater maximum knee-flexion moment, smaller knee-adduction moment, smaller ankle-inversion moment, smaller ground reaction force impact, and earlier multifidus activation. In men and women, fatigue produced a smaller knee-abduction angle at initial contact, greater maximum knee-flexion moment, and delays in semitendinosus, multifidus, gluteus maximus, and rectus femoris activation.Conclusions:Our results provide evidence that during a fatigued 0.30-m landing sequence, women who suffered from recurrent LBP landed differently than did men with recurrent LBP, which may increase women''s exposure to biomechanical factors that can contribute to lower extremity injury.Key Words: clinical biomechanics, rehabilitation, female athletes, anterior cruciate ligament injuries

Key Points

• Sex differences in landing mechanics (fatigued and unfatigued) and neuromuscular control in men and women with recurrent low back pain are similar to the sex differences seen in individuals without a history of low back pain.
• Women experienced a greater knee-flexion angle at initial contact and maximum knee internal rotation, greater maximum knee-flexion moment, smaller maximum knee-adduction and ankle-inversion moments, smaller ground reaction forces at impact, and earlier multifidus activation.
• Reduced knee abduction at initial contact, increased maximum knee-flexion moment, and delayed activation of the semitendinosus, multifidus, gluteus maximus, and rectus femoris muscles were found in both men and women when landing after lower extremity fatigue.
• These changes are consistent with an increased risk of lower extremity injury for women, particularly when landing while fatigued.

Low back pain is a common occurrence in athletes. Estimates of the incidence vary, depending on the sport but range from 10% to 80%.¹ Despite apparent advances in the diagnosis and management of low back pain (LBP), this disorder continues to place a large burden on individuals and society.² Similarly, injuries to the lower extremity frequently affect athletes of all ages, accounting for approximately 53% of all injuries in collegiate athletes.³ Recognizing those at increased risk for back and lower extremity injury and discovering interventions that may reduce that risk are important research goals.Recently, authors^4–8 have proposed a neuromuscular model linking the function of the low back and the lower limbs. Alterations in the operation of this kinetic chain linkage proximally may increase injury risk at more distal regions. Because pelvic stability is influenced by activity of the trunk muscles through their attachments to the pelvis, an inability to properly activate those muscles may create an unstable pelvic base and contribute to altered lower extremity neuromuscular control. Previous studies have shown that activation of the trunk musculature affects lower extremity mechanics. For example, activation of the transversus abdominis significantly decreases activity of the lumbar erector spinae muscles, increases activity of the gluteus maximus and medial hamstrings, and decreases anterior pelvic tilt during prone active hip extension.⁹Trunk-muscle function is altered in LBP sufferers.¹⁰ Therefore, those individuals may not be able to produce sufficient pelvic stability to provide a stable base for lower extremity motion and control. The relationship between LBP and altered lower extremity movement control has been observed in several studies. Individuals with LBP have diminished lower extremity strength, flexibility, and range of motion,^11–13 as well as altered lower extremity biomechanics and neuromuscular control.^14,15 Those changes may increase the risk of lower extremity injury.Authors of prospective clinical studies have linked LBP history with lower extremity injuries. Zazulak et al¹⁶ found that a history of LBP was a significant predictor of knee injury in females and knee-ligament injury in males. Nadler et al¹³ observed that athletes with a history of lower extremity overuse or ligamentous injury were more likely to be treated for LBP during the following year. Additionally, football players with 2 or more of 3 risk factors (trunk-flexion–hold times of less than the median for the team, Oswestry Disability Index scores of 6 or more, or wall–sit-hold times of less than the median for the team) related to low back dysfunction and trunk-muscle endurance were at twice the risk for back and lower extremity injuries than were those with fewer than 2 factors.¹⁷Female athletes are up to 8 times more likely than male athletes to experience an anterior cruciate ligament (ACL) injury and are more prone to injuries from noncontact mechanisms.^18,19 The higher risk for ACL rupture among female athletes has been explained by hormonal, mechanical, neuromuscular, skeletal, and genetic factors.²⁰ The increased incidence of knee-ligament injuries in female athletes is multifactorial; which factors are dominant is currently unknown.²¹ Although both intrinsic and extrinsic factors may contribute, the injury occurs during a loading event, which can be moderated by mechanical and neuromuscular factors.^19,22 Landing technique and neuromuscular function can be improved with training and may potentially reduce the risk of ACL injury.²² Previous investigators have suggested that an increase in quadriceps activation²⁰ and a discrepancy between quadriceps and hamstrings strength may contribute to ACL injuries.²³Female athletes are more likely to sustain certain lower extremity injuries, such as ACL tears. Additionally, females more often develop those injuries as a result of noncontact mechanisms,¹⁸ which may reflect a failure of neuromuscular control because the injury occurs during loading.^19,22 It is unknown whether the occurrence of LBP affects lower extremity biomechanical and neuromuscular responses differently in males versus females.The effects of fatigue on lower extremity control responses in people with recurrent LBP are unknown. Fatigue serves as a major risk factor for lower extremity injury by altering muscle shock-absorbing capacity and coordination of the locomotor system.²⁴ Fatigue can affect neuromuscular input and output pathways.²⁵ Neuromuscular alterations that occur during fatigue potentially increase the risk of injury,^22,23 and muscle fatigue has been linked to a variety of lower extremity injuries.^24–26 Previous researchers²³ have suggested that the order of muscle activation may not change during fatigue, but muscle premotor and reaction phases may be noticeably greater, suggesting a possible compromise in their protective role. Muscle fatigue moderates lower extremity muscle-activation patterns during landing by altering muscle-burst activation, duration, and intensity, as well as the ability of the lower extremity muscles to absorb repetitive shock or stress.^27–29The effects of sex and fatigue on performance and injury risk are well documented.^19,22–24 Recurrent LBP has been established in the literature as a significant predictor of lower extremity injury.^16,17 However, limited information is available on the effects of lower extremity fatigue and sex on lower extremity control during landing in people with recurrent LBP. The purpose of our study was to determine the effects of lower extremity fatigue and sex on knee mechanics, neuromuscular control, and ground reaction force (GRF) during landing in people with recurrent LBP.     

Balance Training and Center-of-Pressure Location in Participants With Chronic Ankle Instability

Context:Chronic ankle instability (CAI) occurs in some people after a lateral ankle sprain and often results in residual feelings of instability and episodes of the ankle''s giving way. Compared with healthy people, patients with CAI demonstrated poor postural control and used a more anteriorly and laterally positioned center of pressure (COP) during a single-limb static-balance task on a force plate. Balance training is an effective means of altering traditional COP measures; however, whether the overall location of the COP distribution under the foot also changes is unknown.Objective:To determine if the spatial locations of COP data points in participants with CAI change after a 4-week balance-training program.Design:Randomized controlled trial.Setting:Laboratory.Intervention(s):Participants were randomly assigned to a 4-week balance-training program or no balance training.Results:Overall, COP position in the balance-training group shifted from being more anterior to less anterior in both eyes-open trials (before trial = 319.1 ± 165.4, after trial = 160.5 ± 149.5; P = .006) and eyes-closed trials (before trial = 387.9 ± 123.8, after trial = 189.4 ± 102.9; P < .001). The COP for the group that did not perform balance training remained the same in the eyes-open trials (before trial = 214.1 ± 193.3, after trial = 230.0 ± 176.3; P = .54) and eyes-closed trials (before trial = 326.9 ± 134.3, after trial = 338.2 ± 126.1; P = .69).Conclusions:In participants with CAI, the balance-training program shifted the COP location from anterolateral to posterolateral. The program may have repaired some of the damaged sensorimotor system pathways, resulting in a more optimally functioning and less constrained system.Key Words: sprains, rehabilitation, postural control

Key Points

• A 4-week progressive balance-training program effectively altered the spatial locations of center-of-pressure data points in participants with chronic ankle instability.
• The alteration in the spatial locations of center-of-pressure data points may indicate a more optimally functioning sensorimotor system.

Lateral ankle ligament injuries are among the most common injuries in the general population, active-duty military service members, and athletes.^1–4 Although the initial symptoms associated with lateral ankle sprains generally resolve in a short time, many patients continue to report residual problems, such as pain, instability, and feelings of the ankle''s giving way.⁵ These residual symptoms have been reported to last 6 to 18 months after initial injury and have been observed in 55% to 72% of patients.^6–8 Repeated incidences of lateral ankle instability, recurrent sprains with persistent symptoms, and diminished self-reported function have been termed chronic ankle instability (CAI).^9,10Postural control requires integration of visual, vestibular, and somatosensory input.¹¹ Somatosensory input combines contributions from cutaneous, articular, and musculotendinous receptors. Afferent information gathered from these 3 sources is processed within the central nervous system and used to control motor commands.¹² Deficient contributions from any of the afferent receptors can lead to diminished postural control.^12–15 Postural-control deficits have been found repeatedly in patients with CAI.^9,10,16–26 These deficits have been identified using a variety of outcome measures, including time to stabilization,^18,22 Star Excursion Balance Test (SEBT) reach distances,¹⁹ center-of-pressure (COP) excursion measures, and time-to-boundary (TTB) measures.^23,27The COP measures from force-plate data can be analyzed to determine the instantaneous point of application of ground reaction forces, and they are useful in evaluating the stability and function of the foot.²⁸ Recently, Pope et al²⁷ evaluated a novel measure, COP location, which involves examining the location of COP data points in relation to the plantar aspect of the foot. Identifying the COP location indicates where the forces are distributed on the foot and provides insight into the postural-control strategy being used. Traditional COP measures and TTB measures cannot elicit the mechanism a person is using to improve balance. The COP location provides information about the spatial distributions of force application under the foot. To determine the COP location, the foot was modeled into a rectangle and divided into 16 equal sections. While the participant performed a single-limb balance task on a force plate, the location of each COP data point was mapped into 1 of the 16 sections. Differences were found between uninjured participants and those with CAI.²⁷ Specifically, COP was more anteriorly and laterally positioned in participants with CAI compared with uninjured persons during eyes-open and eyes-closed single-legged standing.²⁷ The authors hypothesized that this spatial difference may represent a more constrained sensorimotor system and compensatory postural-control mechanisms in participants with CAI.²⁷ Having a more anterolateral COP is likely associated with the foot being more supinated, placing the ankle and subtalar joints in a closed-packed and more stable position that decreases feelings of instability in those with CAI.²⁷ However, this positioning moves the COP closer to the lateral border of support and consequently decreases the amount of time available for postural corrections in this direction.²⁷ Plantar-pressure studies have also demonstrated increased force and pressure concentration under the lateral midfoot and forefoot in participants with CAI during gait, which supports the notion of an anterior and lateral COP shift.^29–31Balance-training programs have been effective in improving postural control in participants with CAI.^28,32–37 McKeon et al²⁸ showed static and dynamic postural-control improvements in a sample of participants with CAI after 4 weeks of balance training that was intended to challenge their sensorimotor systems. Significant improvement occurred in self-reported function, magnitude and variability of TTB measures, and SEBT reach distances compared with pretest and control values.²⁸Although balance improvements have been found after rehabilitation in those with CAI, the neuromechanical mechanism driving these changes is unknown. Determining how the COP location in patients with CAI is affected by a balance-training program may be useful beyond simply evaluating traditional COP measures and also provide insight into how to restore normal function. Understanding how a balance-training rehabilitation program changes COP location offers information on the adaptation strategies participants with CAI use and may enable clinicians to more specifically target each person''s deficits. The purpose of our study, therefore, was to determine how balance training affected COP location. We hypothesized that COP location would be more posteriorly and medially positioned, similar to that of the uninjured participants, after balance training.     

Lower Extremity Landing Biomechanics in Both Sexes After a Functional Exercise Protocol

Context

Sex differences in landing biomechanics play a role in increased rates of anterior cruciate ligament (ACL) injuries in female athletes. Exercising to various states of fatigue may negatively affect landing mechanics, resulting in a higher injury risk, but research is inconclusive regarding sex differences in response to fatigue.

Objective

To use the Landing Error Scoring System (LESS), a valid clinical movement-analysis tool, to determine the effects of exercise on the landing biomechanics of males and females.

Design

Cross-sectional study.

Setting

University laboratory.

Patients or Other Participants

Thirty-six (18 men, 18 women) healthy college-aged athletes (members of varsity, club, or intramural teams) with no history of ACL injury or prior participation in an ACL injury-prevention program.

Intervention(s)

Participants were videotaped performing 3 jump-landing trials before and after performance of a functional, sportlike exercise protocol consisting of repetitive sprinting, jumping, and cutting tasks.

Main Outcome Measure(s)

Landing technique was evaluated using the LESS. A higher LESS score indicates more errors. The mean of the 3 LESS scores in each condition (pre-exercise and postexercise) was used for statistical analysis.

Results

Women scored higher on the LESS (6.3 ± 1.9) than men (5.0 ± 2.3) regardless of time (P = .04). Postexercise scores (6.3 ± 2.1) were higher than preexercise scores (5.0 ± 2.1) for both sexes (P = .01), but women were not affected to a greater degree than men (P = .62).

Conclusions

As evidenced by their higher LESS scores, females demonstrated more errors in landing technique than males, which may contribute to their increased rate of ACL injury. Both sexes displayed poor technique after the exercise protocol, which may indicate that participants experience a higher risk of ACL injury in the presence of fatigue.Key Words: anterior cruciate ligament, fatigue, Landing Error Scoring System

Key Points

• Women consistently demonstrated higher Landing Error Scoring System scores than men, committing more errors in landing technique both before and after exercise.
• The Landing Error Scoring System scores for both sexes increased after exercise, indicating that both males and females were more likely to demonstrate high-risk landing mechanics when fatigued.
• A relatively short period of intense exercise was sufficient to cause detrimental changes in landing mechanics.

An anterior cruciate ligament (ACL) tear is a common and debilitating injury in the athletic population.¹ Approximately 70% of ACL injuries during athletic activities result from a noncontact mechanism involving a deceleration task such as cutting, pivoting, or landing.² Female athletes continue to have a substantially (4 to 6 times) higher risk of noncontact ACL injury than male athletes participating in the same sports.^1,3 In addition to posing a financial burden, ACL injury has multiple long-term health consequences, including functional limitations and a markedly increased risk of disability and osteoarthritis.⁴Researchers have established multiple intrinsic and extrinsic risk factors that may contribute to an individual''s sustaining an ACL injury. It is widely believed that altered movement strategies may be most relevant to females'' increased incidence of noncontact ACL injury.^2,5 Specific movement patterns commonly observed at the time of injury include increased knee valgus and tibial rotation in combination with decreased flexion at the knee, hip, and trunk.^2,5 Laboratory studies^6,7 and video analysis of actual ACL injuries in game situations^2,5 have shown that female athletes are more likely to demonstrate these potentially detrimental landing characteristics than their male counterparts. Individuals displaying these patterns are at greater risk of knee injury.^6,8 The Landing Error Scoring System (LESS) is a clinical movement-assessment tool that can be used to identify these patterns.^9,10An additional factor that may affect injury risk is neuromuscular fatigue.¹¹ Epidemiologic findings support the concept that fatigue may be a predisposing factor for injuries during athletic events.^12,13 Overall injury rates increase during the final minutes of competition^12,13 as well as in the later portions of the season¹² when the effects of fatigue are likely to become cumulative. Specifically, Hawkins and Fuller''s data¹³ indicated that a large percentage of noncontact knee injuries occurred in the last 15 minutes of the first half and the last 30 minutes of the second half of a soccer match. Fatigue has been hypothesized to alter neuromuscular-control factors associated with an increased risk of sustaining musculoskeletal injury. The combination of fatigue with an already high-risk movement pattern may further increase the chance of injury.^11,14,15 If females respond to fatigue differently than males do, this may be an additional risk factor for ACL injuries.¹⁶ However, the specific movement patterns affected remain largely unknown because designs and results vary among studies.Few authors have examined the potential for such changes within the context of an exercise protocol that effectively simulates the demands of sport participation.^11,15 Previous researchers have used exercise protocols that have been short in duration,^11,17–19 consisted only of open kinetic chain tasks,¹⁶ or required participants to repeat a single task such as parallel squats.^14,20 Investigators evaluating longer durations of exercise have used treadmill running or sprinting^18,21 rather than the multidirectional tasks inherent to most sports.The few studies that have incorporated functional tasks have produced various results due to differences in duration and design. After 4 minutes of step-up and bounding tasks, McLean et al¹¹ found changes in only the frontal plane. Both sexes demonstrated increases in knee internal-rotation and abduction motion after exercise, and females demonstrated higher peak abduction moments than males.¹¹ Similarly, after a protocol of repeated vertical jumps and sprints until volitional exhaustion, Chappell et al¹⁵ documented in both sexes an increase in knee-valgus moment and a decrease in knee-flexion angle. Although 4 minutes appears long enough to induce some alterations in landing mechanics, additional changes in sagittal-plane movement have occurred in a study with a slightly longer duration of exercise.¹⁹ After 6 minutes of soccer drills, female National Collegiate Athletic Association Division I soccer players landed with increased knee internal-rotation and decreased knee- and hip-flexion angle. Both a longer duration and incorporation of multidirectional tasks may be necessary to truly assess changes.Whereas such protocols may certainly have placed physical demands on the participants, they do not fully replicate the loading conditions sustained by the lower extremity during athletic activity. In order to obtain the most relevant findings and apply conclusions to the athletic population, we developed a functional exercise protocol consisting of a variety of multidirectional tasks and sought to extend the duration compared with that of previous studies.^11,15,19 To make our study as clinically relevant as possible, we chose the LESS to evaluate landing technique.⁹ It is a valid and reliable clinical movement-assessment tool that allows for efficient evaluation of high-risk movement patterns.⁹By using a sportlike protocol and the clinical assessment of a landing task, our exercise tasks and assessment tool are applicable to the athletic population and feasible for use by clinicians. Considering the relationship of landing mechanics to noncontact ACL injury, studying the effects of exercise on biomechanical characteristics while in a fatigued state may provide insight into injury risk.^{11,14,15,17,20} Therefore, the purpose of this study was to assess the effects of fatigue induced by a functional exercise protocol on the landing biomechanics of males and females. We hypothesized that females would commit more landing errors than males in both the preexercise and postexercise conditions. Furthermore, we hypothesized that the exercise protocol would have a detrimental effect on all participants'' landing biomechanics, causing them to commit more errors after the protocol. Last, we hypothesized that these exercise-induced changes would be more prominent in females than in males.     

Soccer-Specific Warm-Up and Lower Extremity Injury Rates in Collegiate Male Soccer Players

Context:

A number of comprehensive injury-prevention programs have demonstrated injury risk-reduction effects but have had limited adoption across athletic settings. This may be due to program noncompliance, minimal exercise supervision, lack of exercise progression, and sport specificity. A soccer-specific program described as the F-MARC 11+ was developed by an expert group in association with the Federation Internationale de Football Association (FIFA) Medical Assessment and Research Centre (F-MARC) to require minimal equipment and implementation as part of regular soccer training. The F-MARC 11+ has been shown to reduce injury risk in youth female soccer players but has not been evaluated in an American male collegiate population.

Objective:

To investigate the effects of a soccer-specific warm-up program (F-MARC 11+) on lower extremity injury incidence in male collegiate soccer players.

Design:

Cohort study.

Setting:

One American collegiate soccer team followed for 2 seasons.

Patients or Other Participants:

Forty-one male collegiate athletes aged 18–25 years.

Intervention(s):

The F-MARC 11+ program is a comprehensive warm-up program targeting muscular strength, body kinesthetic awareness, and neuromuscular control during static and dynamic movements. Training sessions and program progression were monitored by a certified athletic trainer.

Main Outcome Measure(s):

Lower extremity injury risk and time lost to lower extremity injury.

Results:

The injury rate in the referent season was 8.1 injuries per 1000 exposures with 291 days lost and 2.2 injuries per 1000 exposures and 52 days lost in the intervention season. The intervention season had reductions in the relative risk (RR) of lower extremity injury of 72% (RR = 0.28, 95% confidence interval = 0.09, 0.85) and time lost to lower extremity injury (P < .01).

Conclusions:

This F-MARC 11+ program reduced overall risk and severity of lower extremity injury compared with controls in collegiate-aged male soccer athletes.Key Words: injury prevention, sport injuries, athletic trainers

Key Points

• The F-MARC 11+ reduced the risk of lower extremity injuries in youth female soccer players, but limited evidence for its effectiveness exists in males and at the collegiate level.
• A traditional warm-up did not prevent injury as effectively as the F-MARC 11+ program, despite taking the same amount of time.
• When supervised by an athletic trainer, the F-MARC 11+ prevented injuries in collegiate male soccer players.
• An athletic trainer administered intervention, reduced injury risk, and improved program compliance, progression, and execution.

Soccer is among the most popular sports in the world, boasting more than 265 million¹ youth and amateur players and more than 37 000 American collegiate players.² Soccer participation has continued to increase over the past decade worldwide and especially in the United States National Collegiate Athletic Association (NCAA).² Lower extremity injury rates for male NCAA soccer athletes have remained relativity stable over the past decade (practice versus game: 8 versus 12.18 per 1000 exposures).² Junge and Dvorak,³ in a systematic review of soccer injuries in international male players, reported 10 to 35 injuries per 1000 hours of match play and 2 to 7 per 1000 hours of training in international male soccer players. In cohorts of international, elite-level soccer athletes, the injury rate was high (1.3 injuries per player per season); most injuries affected the lower extremity (87%) and resulted from noncontact mechanisms (58%).⁴ The most common injury in male collegiate soccer players was ankle sprains (3.19 per 1000 exposures), followed by thigh muscle strains and knee sprains at 2.28 and 2.07 per 1000 exposures, respectively.² These findings are consistent with reports of international-level soccer athletes.⁴ These lower extremity injuries have substantial short-term consequences, such as loss of participation, and the potential for long-term consequences, such as decreased physical activity⁵ and increased risk of osteoarthritis.^5–10 Nearly 20% of all soccer injuries were severe, requiring greater than 10 days of time lost from activity.² Knee ligament ruptures and leg fractures accounted for 35% of these injuries, many of which required surgical intervention and prolonged rehabilitative care; these patients also had a greatly increased risk of a secondary injury when they returned to soccer competition.^2,11The high injury rate in soccer players has persisted despite scientific advances in injury etiology,^12–17 screening techniques, and the identification of athletes who may be at greater risk.^18–25 Although injury-prevention programs have successfully decreased lower extremity injuries such as ankle sprains,^24,26–29 anterior cruciate ligament (ACL) injuries,^18,30,31 and hamstrings strains,^{20,24,29,32–34} they have not yet been widely adopted,³⁵ limiting their potential effects in soccer athletes.³⁶Although numerous training programs have been designed to prevent injury,^{3,24,26,29,31,32,37–55} few incorporate sport-specific components.^{37,38,41,42,56,57} Many of these programs have shown promising results in decreasing the risk of injury.^{18,37,38,41,58} However, extensive time, expert personnel, and special equipment are needed for these programs to be effective. To make injury-prevention programs as widely accessible as possible, the F-MARC 11+ program was developed by the Federation International de Football Association (FIFA) Medical Assessment and Research Center (F-MARC).⁵⁹ This program can be completed in a short time frame, takes minimal training to implement, and requires only a soccer ball, making it an attractive alternative for sport coaches, strength and conditioning professionals, and rehabilitation specialists already working with limited time and budgets. Thus far, 4 studies^37,38,41,60 have reported on the use of a version of the F-MARC 11+ program in adolescent males and females, with injury reductions ranging from 21% to 71%. In Norwegian handball players, similar training programs have produced a 49% reduction in injury risk⁴⁰ and 94% reduction in ACL injury risk.³⁹To our knowledge, the F-MARC 11+ has yet to be investigated for effectiveness in injury risk reduction in an American male collegiate soccer population. Therefore, our aim was to examine the effect of a sport-specific program implemented with athletic trainer supervision to track compliance, injury occurrence, and program performance quality. We hypothesized that the comprehensive, exercise-based soccer warm-up program (the F-MARC 11+) would be more effective than the traditional dynamic warm-up in preventing lower extremity injuries in male NCAA Division III collegiate soccer athletes.     

Chronic Ankle Instability and Neural Excitability of the Lower Extremity

Context

Neuromuscular dysfunction of the leg and thigh musculature, including decreased strength and postural control, is common in patients with chronic ankle instability (CAI). Understanding how CAI affects specific neural pathways may provide valuable information for targeted therapies.

Objective

To investigate differences in spinal reflexive and corticospinal excitability of the fibularis longus and vastus medialis between limbs in patients with unilateral CAI and between CAI patients and participants serving as healthy controls.

Design

Case-control study.

Setting

Research laboratory.

Patients or Other Participants

A total of 56 participants volunteered, and complete data for 21 CAI patients (9 men, 12 women; age = 20.81 ± 1.63 years, height = 171.57 ± 11.44 cm, mass = 68.84 ± 11.93 kg) and 24 healthy participants serving as controls (7 men, 17 women; age = 22.54 ± 2.92 years, height = 172.35 ± 10.85 cm, mass = 69.15 ± 12.30 kg) were included in the final analyses. Control participants were matched to CAI patients on sex, age, and limb dominance. We assigned “involved” limbs, which corresponded with the involved limbs of the CAI patients, to control participants.

Main Outcome Measure(s)

Spinal reflexive excitability was assessed via the Hoffmann reflex and normalized to a maximal muscle response. Corticospinal excitability was assessed using transcranial magnetic stimulation. Active motor threshold (AMT) was defined as the lowest transcranial magnetic stimulation intensity required to elicit motor-evoked potentials equal to or greater than 100 μV in 5 of 10 consecutive stimuli. We obtained motor-evoked potentials (MEPs) at percentages ranging from 100% to 140% of AMT.

Results

Fibularis longus MEP amplitudes were greater in control participants than in CAI patients bilaterally at 100% AMT (control involved limb: 0.023 ± 0.031; CAI involved limb: 0.014 ± 0.008; control uninvolved limb: 0.021 ± 0.022; CAI uninvolved limb: 0.015 ± 0.007; F_1,41 = 4.551, P = .04) and 105% AMT (control involved limb: 0.029 ± 0.026; CAI involved limb: 0.021 ± 0.009; control uninvolved limb: 0.034 ± 0.037; CAI uninvolved limb: 0.023 ± 0.013; F_1,35 = 4.782, P = .04). We observed no differences in fibularis longus MEP amplitudes greater than 110% AMT and no differences in vastus medialis corticospinal excitability (P > .05). We noted no differences in the Hoffmann reflex between groups for the vastus medialis (F_1,37 = 0.103, P = .75) or the fibularis longus (F_1,41 = 1.139, P = .29).

Conclusions

Fibularis longus corticospinal excitability was greater in control participants than in CAI patients.Key Words: transcranial magnetic stimulation, Hoffmann reflex, lateral ankle sprain

Key Points

• Corticospinal excitability in the fibularis longus at transcranial magnetic stimulation intensities of 100% and 105% of active motor threshold was higher in the healthy control group bilaterally than in the chronic ankle instability group.
• Transcranial magnetic stimulation intensities at 110% or more of the active motor threshold did not result in differences between groups.
• Corticospinal excitability of the quadriceps did not differ between groups.
• Spinal reflexive excitability of the fibularis longus and quadriceps did not differ between groups.

Ankle sprains are common musculoskeletal injuries, with an estimated 23 000 injuries per day in the United States.¹ Recurrent ankle sprains have been reported to occur in as many as 80% of patients with ankle injuries.² Multiple recurrent ankle sprains are thought to be a complication of chronic ankle instability (CAI),³ which is a multifactorial pathologic condition hypothesized to originate from both mechanical insufficiencies and functional deficits.^3,4 Mechanical insufficiencies include pathologic joint laxity and altered arthrokinematics; functional deficits may include impaired postural control and decreased strength and neuromuscular control.^3,4 Chronic ankle instability results in self-reported disability, and the cumulative effect of multiple ankle sprains may hasten the progression of joint degeneration and osteoarthritis. Therefore, advancing rehabilitative approaches is critical to improve disability and decrease the risk of multiple ankle sprains in individuals with CAI.Current nonoperative approaches to improve functional deficits in CAI patients have targeted clinical impairments associated with altered movement strategies that may increase the risk of ankle sprain.^5,6 Patients with CAI have been observed to exhibit impaired postural control,⁷ decreased muscle strength,⁸ and altered ankle range of motion during jogging⁹ and landing tasks.^10–12 They also exhibit less control of their center of pressure relative to the boundaries of their feet during single-limb stance¹³ and take longer to stabilize after landing from a jump^14–16 than healthy control participants. Patients with CAI have exhibited decreased plantar-flexor¹⁷ and ankle-evertor muscle strength⁸ and delayed muscle-firing patterns in the fibularis musculature when perturbed while walking.¹⁸ Ankle-dorsiflexion deficits⁹ and increased subtalar-inversion and shank external-rotation ranges of motion have been demonstrated during both walking and jogging in CAI patients compared with healthy control participants.¹⁹Altered muscle function after joint injury has been hypothesized to have neural origins rooted partially in a clinical impairment known as the arthrogenic muscle response.²⁰ This impairment is characterized by an abnormal facilitation or inhibition of neural drive to the undamaged musculature surrounding an injured joint. The central nervous system controls muscle contraction and modulates movements via spinal reflexive and corticospinal pathways.²¹ Patients with ankle instability have decreased spinal reflexive excitability of the fibularis longus and soleus muscles, measured via the Hoffmann reflex (H-reflex), compared with healthy counterparts.²² Similarly, corticospinal excitability of the fibularis longus in CAI patients has been shown to be diminished when compared with healthy participants assessed using transcranial magnetic stimulation (TMS).²³ Neuromuscular control adaptations in joints proximal to the ankle also have been demonstrated in patients with CAI, manifesting as deficits in force production,^17,24 changes in kinematic patterns,^{10,11,14,25–27} and deficits in muscle-activation patterns^12,28–31 about the knee and hip during slow and dynamic tasks. Whereas these alterations are observed consistently, the source of these changes has not been established.Pathologic ankle conditions result in spinal-level pathway alterations,^22,32 which can lead to feed-forward patterns that present as changes in knee and hip neuromuscular control.^11,14,27 Sedory et al³¹ reported that the excitability of multiple muscle groups proximal to the ankle was altered in people with CAI, suggesting that higher brain centers may be influencing motor function. In addition, Heroux and Tremblay³³ suggested that cortical excitability is altered in the quadriceps musculature after knee injuries. However, to our knowledge, few researchers have evaluated the effects of ankle instability on corticomuscular control in this population. These theories of the influence of higher brain centers have been developed using biomechanical research tools that provide indirect information about nerve function. To fully appreciate these theories, it is necessary to directly compare the nerve pathway function between the pathologic ankles, as well as proximal to the ankles, of CAI patients and the ankles and proximal regions of healthy populations. Understanding how both spinal reflexive and cortical excitability are affected in proximal and distal musculature is important for developing multimodal interventions that can target the origins of neuromuscular dysfunction at multiple points throughout the injured extremity. Therefore, the purpose of our study was to determine if corticospinal and spinal reflexive excitability of the fibularis longus and quadriceps differed between individuals with CAI and healthy control participants. We hypothesized that both spinal reflexive and corticospinal excitability would differ in the fibularis longus and the vastus medialis between those with CAI and their healthy control counterparts.     

Career and Family Aspirations of Female Athletic Trainers Employed in the National Collegiate Athletic Association Division I Setting

Context:Female athletic trainers (ATs) tend to depart the profession of athletic training after the age of 30. Factors influencing departure are theoretical. Professional demands, particularly at the collegiate level, have also been at the forefront of anecdotal discussion on departure factors.Objective:To understand the career and family intentions of female ATs employed in the collegiate setting.Design:Qualitative study.Setting:National Collegiate Athletic Association Division I.Results:Our participants indicated a strong desire to focus on family or to start a family as part of their personal aspirations. Professionally, many female ATs were unsure of their longevity within the Division I collegiate setting or even the profession itself, with 2 main themes emerging as factors influencing decisions to depart: family planning persistence and family planning departure. Six female ATs planned to depart the profession entirely because of conflicts with motherhood and the role of the AT. Only 3 female ATs indicated a professional goal of persisting at the Division I setting regardless of their family or marital status, citing their ability to maintain work-life balance because of support networks. The remaining 17 female ATs planned to make a setting change to balance the roles of motherhood and AT because the Division I setting was not conducive to parenting.Conclusions:Our results substantiate those of previous researchers, which indicate the Division I setting can be problematic for female ATs and stimulate departure from the setting and even the profession.Key Words: retention, attrition, work-life balance

Key Points

• Female athletic trainers decided to depart the Division I setting because the required hours of the job limited the time available for parenting.
• Female athletic trainers working in the Division I setting who were able to persist after having a family credit strong support networks and the development of effective work-life balance strategies.

Traditionally, working women endure more challenges balancing career demands and family responsibilities than working men, often because of their mothering philosophies and traditional gender stereotypes.¹ Surprisingly, gender differences have not been found in the occurrence of conflicts between work and life in the athletic training profession.^2,3 This finding is perplexing because female athletic trainers (ATs) continue to depart from the profession.⁴ Hypothetically, the decline in the number of female ATs in the profession has been linked to the desire to strike a balance among work responsibilities, personal interests, and family obligations.^1–3,5Concerns about work-life balance (WLB) and time for parenting have been found to influence decisions to persist within the collegiate levels, as the job responsibilities often include long hours (>40 h/wk) and travel, which can limit time spent at home with family.^1–3,5 It is an unfortunate reality that female ATs make up only approximately 28% of the full-time collegiate staff.⁵ This is especially concerning when the National Athletic Trainers'' Association indicates that more than 50% of its members are female.⁶ A relationship appears to exist between balancing professional responsibilities with parenthood and retention factors, especially for those who leave the collegiate clinical setting to work in clinical settings more favorable to family life.Female ATs in the National Collegiate Athletic Association Division I setting experience great challenges in maintaining WLB because of the demands of the setting.¹ In a recent study,¹ the primary reasons female ATs continued in the Division I setting were enjoyment of the job and atmosphere, increased autonomy, positive athlete dynamics, and the social support network. It is important for female ATs to have support at work and home to persist in the collegiate or athletic training clinical setting. However, long work hours and the inability to find WLB can stress this support network. Mazerolle and colleagues^2,3 first proposed that motherhood plausibly could lead to departure from the profession as the result of a myriad of factors but mostly because of a lack of time and control over work schedules. Further investigations have supported this theory and also have found that other reasons for leaving the profession are WLB concerns, supervisory and coach conflicts, caring for children, and role overload.^1,4,5Fulfillment of WLB is an important retention factor for female coaches within the collegiate setting,⁷ thus providing some supporting evidence to the suppositions that motherhood can be a mediating factor in the retention of female ATs in the collegiate setting. Additional support can be garnered from Mazerolle et al,² who found that only 22 female ATs with children were employed at the collegiate setting, a statistic supported by Kahanov et al,⁵ who reported that only about a quarter of all full-time ATs at the collegiate setting were female.Concerns about retention, particularly of female ATs, have become an increasingly popular topic within the athletic training literature, with attention focused on the collegiate clinical setting. This setting not only is one of the largest employment settings for the AT⁶ but is recognized as a time-intensive, demanding work environment.^2,3,8,9 Moreover, data suggest women are leaving this particular clinical setting to find a more family-friendly work environment, which may or may not be in the profession of athletic training.^10,11 Additionally, 2 recent studies^10,11 suggest that female athletic training students intend to pursue careers in athletic training, but as highlighted by Kahanov and Eberman,⁴ women are rapidly departing the profession for a variety of reasons. The emigration of female ATs from the profession has been theoretically associated with the desire to attain balance among family commitments, personal time, and work responsibilities.^1,2 Difficulties maintaining WLB and sufficient time for parenting shape decisions to continue at the collegiate level.^1,2Because of the concerning trend of female AT attrition, the purpose of our study was to understand the perspectives of female ATs, regardless of marital status, and to evaluate career and family intentions. Our objective was to gain a more thorough understanding of female ATs'' professional goals as they may be influenced by family planning. Our research questions included, “What factors influence the career intentions of female ATs regarding career longevity?” and “Do female ATs have intentions to remain in the NCAA Division I setting?”     

Sport-Related Concussion and Sensory Function in Young Adults

Context:

The long-term implications of concussive injuries for brain and cognitive health represent a growing concern in the public consciousness. As such, identifying measures sensitive to the subtle yet persistent effects of concussive injuries is warranted.

Objective:

To investigate how concussion sustained early in life influences visual processing in young adults. We predicted that young adults with a history of concussion would show decreased sensory processing, as noted by a reduction in P1 event-related potential component amplitude.

Design:

Cross-sectional study.

Setting:

Research laboratory.

Patients or Other Participants:

Thirty-six adults (18 with a history of concussion, 18 controls) between the ages of 20 and 28 years completed a pattern-reversal visual evoked potential task while event-related potentials were recorded.

Main Outcome Measure(s):

The groups did not differ in any demographic variables (all P values > .05), yet those with a concussive history exhibited reduced P1 amplitude compared with the control participants (P = .05).

Conclusions:

These results suggest that concussion history has a negative effect on visual processing in young adults. Further, upper-level neurocognitive deficits associated with concussion may, in part, result from less efficient downstream sensory capture.Key Words: mild traumatic brain injuries, visual processing, event-related potentials, pattern-reversal visual evoked potentials

Key Points

• Visual processing and higher-level cognitive function were affected by concussion over the long term.
• The potential contributions of low-level sensory deficits to higher-order neurocognitive dysfunction after concussion should be studied.
• Event-related potentials have greater sensitivity than standard clinical tools and have the potential for clinical use.

The long-term and cumulative effects of concussive injuries represent a growing concern in the public consciousness. Concussion has been defined as “a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces.”^1,2 Estimated incidence rates for this condition, described as a “silent epidemic” by the Centers for Disease Control and Prevention,^2–5 range from a conservative 300 000 per year^4–6 to a more liberal and recent estimate of 3.8 million cases in the United States annually.⁷ Because 15% to 20% of these injuries result from sport participation,⁸ sport-related concussion represents an increasing concern, not only in the public domain but also in clinical and research settings.Based on clinical evaluations, concussed persons typically return to their preinjury level of functioning within 7 to 10 days of injury,^9,10 a time paralleling the acute neurometabolic cascade associated with concussion.^11,12 Indeed, several investigations^2,13–15 of young adult athletes with a concussion history indicate normal performance on a variety of clinical tests after the acute injury stage. However, more recent studies using highly sensitive assessment measures suggest that a multitude of chronic nervous system dysfunctions and cognitive deficits stem from concussive injuries.^16–28 Thus, the chronic, subclinical effects of concussion remain unclear, and measures sensitive to subtle and persistent deficits stemming from concussion are needed.Electroencephalography, which records brain activity from electrodes placed on the scalp, has been extensively used to examine neuroelectric activity in normal and clinical populations for almost a century. More recently, event-related potentials (ERPs; patterns of neuroelectric activity that occur in preparation for or in response to an event) have emerged as a technique to provide insight into the neural processes underlying perception, memory, and action.²⁹ The ERPs may be obligatory responses (exogenous) to stimuli in the environment or may reflect higher-order cognitive processes (endogenous) that often require active consideration by a person.³⁰Over the past decade, electroencephalography and ERPs in particular have demonstrated the requisite sensitivity to detect subtle, covert deficits in neurocognitive function associated with concussion^{17,23,27,31–33} (for review, see Broglio et al²⁹). Although several groups have evaluated ERP components, such as the ERN, N2, and P3, to examine attention, perception, and memory, few authors^23,34–36 have evaluated the effects of concussion on neuroelectric indexes of sensory function. In particular, only 3 studies have evaluated the influence of concussion on visual-evoked potentials (VEPs).^23,34,35 Findings from these studies suggest that for a significant portion of people, concussion may lead to chronic impairment in the neuroelectric correlates of visual processing.Believed to reflect the functional integrity of the visual system, VEPs are electrophysiologic signals passively evoked in response to visual stimuli that demonstrate a parietal-occipital maximum.^37–40 Efficient visual processing and sensory integration are essential to day-to-day functioning^34,41; however, the visual system of a concussed individual is typically unevaluated.³⁴ Thus, VEPs represent an underused and potentially valuable tool for evaluating and understanding sensory and nervous system dysfunction after injury.One VEP paradigm of particular utility is the pattern-reversal task (PR-VEP). This task uses an inverting patterned stimulus to evoke an electrocortical waveform, which is characterized by a negative deflection at about 75 milliseconds (N75), followed by a positive deflection at about 100 milliseconds (P1).⁴² The PR-VEP task is a standard in clinical research assessing central nervous system function⁴³ because of the high sensitivity, specificity, and intraindividual stability of PR-VEPs relative to VEPs elicited by other paradigms.^44,45 Specifically, the P1 elicited by this paradigm is less variable than the P1 components elicited by other paradigms, making it preferable for evaluating clinical populations.⁴⁰ For example, Sarnthein et al⁴⁵ observed a test-retest sensitivity of 95% and specificity of 99.7% for P1 component values. Further, Mellow et al,⁴⁶ evaluating binocular reproducibility in a single participant, observed test-retest coefficients of variation of 9% to 14% for P1 amplitude and 1% to 2% for P1 latency.The P1 component is an exogenous or obligatory potential and is the first positive-going deflection after stimulus presentation (or inversion). The P1 is thought to reflect sensory processes such as gating, amplification, and preferential attention to sensory inputs.^38,47 Within the context of the PR-VEP paradigm, the P1 is believed to index the functioning of the geniculostriatal pathway,³⁹ which is thought to mediate visual processing. The P1 component values can provide important information to researchers and clinicians: reduced P1 amplitude may indicate neuronal atrophy,⁴⁸ and increased P1 latency may indicate slowed neural conduction within the visual pathways.⁴⁹To our knowledge, only one set of authors²³ has evaluated the P1 component in relation to sport-induced concussion by using a pattern-reversal task to elicit VEPs in young and middle-aged adults. Approximately one-third of the participants who reported a concussion history evidenced P1 deficits, as determined by clinical diagnostic criteria. Such findings suggest that concussion may negatively influence the P1 component in a subset of persons, but further investigation is warranted to clarify the nature of the relationship between concussive injuries and the P1 VEP. Accordingly, the purpose of our investigation was to assess the relationship of sport-related concussion on visual processing using a pattern-reversal paradigm.     

Ankle-Dorsiflexion Range of Motion After Ankle Self-Stretching Using a Strap

Context A variety of ankle self-stretching exercises have been recommended to improve ankle-dorsiflexion range of motion (DFROM) in individuals with limited ankle dorsiflexion. A strap can be applied to stabilize the talus and facilitate anterior glide of the distal tibia at the talocrural joint during ankle self-stretching exercises. Novel ankle self-stretching using a strap (SSS) may be a useful method of improving ankle DFROM.Objective To compare the effects of 2 ankle-stretching techniques (static stretching versus SSS) on ankle DFROM.Design Randomized controlled clinical trial.Setting University research laboratory.Results Active DFROM and PDFROM were greater in both stretching groups after the 3-week interventions. However, ADFROM, PDFROM, and the lunge angle were greater in the SSS group than in the static-stretching group (P < .05).Conclusions Ankle SSS is recommended to improve ADFROM, PDFROM, and the lunge angle in individuals with limited DFROM.Key Words: limited ankle dorsiflexion, rehabilitation, injury prevention

Key Points

• Ankle self-stretching using a strap is a novel stretching technique used to improve ankle-dorsiflexion range of motion. It is more effective than static stretching and can be performed independently.
• For athletes with limited ankle range of motion, self-stretching with a strap can be recommended to improve their ankle-dorsiflexion range of motion and performance in functional and sports activities.
• The lunge angle was enhanced more with ankle self-stretching using a strap than with static stretching after 3-week interventions.

Ankle stretching has been considered an essential part of rehabilitation and physical fitness programs for injury prevention and improvement of ankle function.¹ Limited dorsiflexion range of motion (DFROM) may contribute to ankle, foot, and knee injuries, including plantar fasciitis,^2,3 ankle sprains,⁴ Achilles tendinitis,⁵ forefoot pain,⁶ navicular stress fractures,⁷ calf muscle tightness,⁸ Achilles tendinopathy,⁹ and anterior cruciate ligament injury.¹⁰ Limited DFROM may be associated with various factors, such as tightness in the plantar flexors (gastrocnemius and soleus), soft tissue and capsular restriction, and loss of accessory motion at the tibiotalar, subtalar, tibiofibular, and midtarsal joints.¹¹ Posterior gliding of the talus should occur during ankle dorsiflexion (DF)^12,13; reduced posterior gliding of the talus can contribute to limited DFROM.Various interventions including static stretching,¹⁴ runner''s stretching,¹⁵ mobilization with movement (MWM),^16,17 talus-stabilizing–taping (TST) techniques,^5,18 and orthoses¹⁹ have been used to increase DFROM and prevent ankle and foot injuries in individuals with limited DFROM. Two mobilization techniques are available to improve DFROM. One traditional MWM technique is performed passively to glide the talus posteriorly in a non–weight-bearing position. Another MWM technique is performed in a weight-bearing position to improve DFROM, provide pain relief, and allow functional activities such as lunging and squatting.^17,18 Mobilization with movement can be applied with combined manual force by a therapist to glide the talus posteriorly and permit active DF in a weight-bearing position.¹⁷ Previous authors^17,20 found that for individuals with limited DFROM, MWM techniques using weight-bearing exercises were more effective than techniques with a non–weight-bearing component. However, the MWM technique for ankle DF requires a therapist''s hand to stabilize the ankle joint,^5,17 making it difficult for individuals to perform MWM independently.Two methods have been introduced to facilitate posterior gliding of the talus during ankle DF exercises in a weight-bearing position.^5,18 Using the TST method during walking has also been suggested to increase DFROM.⁵ Another ankle self-stretching DF exercise uses a towel to perform posterior glide of the talus during closed chain DF activity.¹⁸ The MWM and TST methods, which use talar posterior gliding in the closed chain position, have been recommended for improving DFROM. Self-MWM towel- or strap-based techniques were introduced by Mulligan²¹ to enable unrestricted movement without pain in the majority of joints in the body.²² An additional ankle self-mobilization technique using a towel to provide posterior glide of the talus during closed chain DF activity has also been proposed.¹⁸ Self-mobilization using a strap can increase wrist-extension range of motion and decrease wrist pain.²³ Therefore, we investigated whether strap-based stretching for talar posterior gliding was more effective than static stretching. To provide a self-stretching technique for facilitating gliding motion in the talocrural joint in the weight-bearing–lunge position, we designed the novel technique termed ankle self-stretching using a strap (SSS) for individuals with limited ankle DFROM.To perform SSS, a strap approximately 30 cm long is tied to the anterior aspect of the talus on the front of the foot, which is on a 10° incline board, and the back of the strap is placed around the medial region of the plantar aspect of the foot on the ground to pull the talus in the posterior-inferior direction. The strap can be used to provide stability at the talus by pulling it during the lunge exercise.^5,18 Because the pulling force is applied during the lunge, SSS can affect both the musculotendinous tightness of the soleus and the arthrokinematic restriction of the talocrural joint, thereby improving DFROM. Additionally, during SSS, if the strap-pulling force is independently applied to specific regions of the ankle joint, SSS could be more effective than conventional static stretching.In this study, we used conventional static stretching because it is among the most frequently self-applied static-position techniques.²⁴ However, SSS can be applied independently in the dynamic-lunge position using talar stabilization to improve ankle DFROM.^1,5,15 Thus, the aim of our study was to determine the effects of SSS on improvements in active DFROM (ADFROM), passive DFROM (PDFROM), and the lunge angle compared with static stretching. We hypothesized that SSS would increase ankle DFROM to a greater degree than static stretching would.     

High-Intensity Running and Plantar-Flexor Fatigability and Plantar-Pressure Distribution in Adolescent Runners

Context:Fatigue-induced alterations in foot mechanics may lead to structural overload and injury.Objectives:To investigate how a high-intensity running exercise to exhaustion modifies ankle plantar-flexor and dorsiflexor strength and fatigability, as well as plantar-pressure distribution in adolescent runners.Design:Controlled laboratory study.Setting:Academy research laboratory.Intervention(s):All participants performed an exhausting run on a treadmill. An isokinetic plantar-flexor and dorsiflexor maximal-strength test and a fatigue test were performed before and after the exhausting run. Plantar-pressure distribution was assessed at the beginning and end of the exhausting run.Results:Isokinetic peak torques were similar before and after the run in both muscle groups, whereas the fatigue index increased in plantar flexion (28.1%; P = .01) but not in dorsiflexion. For the whole foot, mean pressure decreased from 1 minute to the end (−3.4%; P = .003); however, mean area (9.5%; P = .005) and relative load (7.2%; P = .009) increased under the medial midfoot, and contact time increased under the central forefoot (8.3%; P = .01) and the lesser toes (8.9%; P = .008).Conclusions:Fatigue resistance in the plantar flexors declined after a high-intensity running bout performed by adolescent male distance runners. This phenomenon was associated with increased loading under the medial arch in the fatigued state but without any excessive pronation.Key Words: ankle, medial longitudinal arch, isokinetic exercise, pronation

Key Points

• High-intensity running to exhaustion affected resistance to fatigue of the ankle plantar flexors in adolescent male athletes.
• Loading increased under the medial arch in the fatigued state without excessive pronation.
• Mechanisms underpinning fatigue-induced pronation should be interpreted with caution because these adaptations are complex and multifactorial.

Researchers have reported changes in plantar-pressure distribution, including increased peak plantar-pressure and impulse values in the forefoot and concomitant reductions under the toe areas, among individuals running in a fatigued state.^1,2 A top-down theory,³ in which the proximal musculature (weakness or fatigue) at the hip may be contributing to the changes in distal joint mechanics, may be a plausible framework. This shift in load from the toes to the metatarsal heads also may arise from fatigue in the lower limb and foot musculature (ie, the toe flexor muscles² or the ankle plantar flexors¹) and may be explained by reductions in the stretch-shortening capabilities of the plantar flexors, subsequently leading to reduced toe-off efficiency.⁴ Researchers^5,6 have proposed 2 other mechanisms. First, in fatigued conditions, participants may change from a heel-toe to midfoot landing strategy.⁵ Second, increased first metatarsal loading may reflect an increase in foot pronation induced by fatigue of the musculature responsible for controlling this movement.^6,7 In the last decade, dynamic plantar pressure has been used widely to assess the pressure distribution under the feet of participants with pathologic conditions and under normal feet. Although no direct link between plantar pressure and joint motion has been established, investigators^8,9 think that some changes in plantar-pressure distribution, such as excessive peak plantar pressure under the medial forefoot and midfoot or a decrease in peak plantar pressure under the lateral forefoot and midfoot, reflect excessive pronation. Overall, changes in subtalar alignment during the stance phase (ie, excessive pronation) lead to subsequent changes in plantar-pressure distribution.^8,9Fatigue due to high-intensity running can lead to alterations in lower limb biomechanics, including increased impact forces⁷ and increased rear-foot motion.¹⁰ These alterations may result in overload of the bony structures in the legs and feet, increasing the potential for overuse injury,¹ especially in adolescent distance runners with immature skeletal development.¹⁰ Indeed, in adolescent athletes, endurance sports that involve recurrent, regular cyclic stressing of the lower extremities may lead to stress fractures in the metatarsal bones.¹⁰Isokinetic dynamometry assessments, which involve calculating changes in peak torque from pre-exercise to postexercise, are relevant for assessing muscle-force changes in muscle function after fatiguing exercise.¹¹ Specific isokinetic protocols to assess muscle fatigability have been proposed and involve a predetermined number of reciprocal maximal concentric contractions at a given angular velocity.^12–14 Despite the emergence of such tests, isokinetic measures have rarely been used to assess the torque changes induced by a running bout.^4,15 Moreover, to our knowledge, the relationship between lower limb muscle fatigability and alterations in plantar-pressure distribution during a run to exhaustion has not been investigated. Therefore, the purpose of our study was to determine the extent to which running to exhaustion modified plantar-flexor and dorsiflexor strength and fatigability and plantar-pressure distribution. We hypothesized that (1) running-induced fatigue would result in loss of plantar-flexor and dorsiflexor strength and endurance and (2) changes resulting from localized calf-muscle fatigue may be associated with abnormal loading (eg, increased peak plantar pressure at the medial forefoot and midfoot).     

Whole-Body Vibration While Squatting and Delayed-Onset Muscle Soreness in Women

Context Research into alleviating muscle pain and symptoms in individuals after delayed-onset muscle soreness (DOMS) has been inconsistent and unsuccessful in demonstrating a useful recovery modality.Objective To investigate the effects of short-term whole-body vibration (WBV) on DOMS over a 72-hour period after a high-intensity exercise protocol.Design Randomized controlled clinical trial.Setting University laboratory.Intervention(s) Participants performed 4 sets to failure of single-legged split squats with 40% of their body weight to induce muscle soreness in the quadriceps. The WBV or control treatment was administered each day after DOMS.Results We observed no interactions for PPT, thigh circumference, and muscle pain (P > .05). An interaction was found for active ROM (P = .01), with the baseline pretreatment measure greater than the measures at baseline posttreatment 1 through 48 hours posttreatment 2 in the WBV group. For PPT, a main effect for time was revealed (P < .05), with the measure at baseline pretreatment greater than at 24 hours pretreatment and all other time points for the vastus medialis, greater than 24 hours pretreatment through 48 hours posttreatment 2 for the vastus lateralis, and greater than 24 hours pretreatment and 48 hours pretreatment for the rectus femoris. For dynamic muscle pain, we observed a main effect for time (P < .001), with the baseline pretreatment measure less than the measures at all other time points. No main effect for time was noted for thigh circumference (P = .24). No main effect for group was found for any variable (P > .05).Conclusions The WBV treatment approach studied did not aid in alleviating DOMS after high-intensity exercise. Further research is needed in various populations.Key Words: range of motion, edema, pressure-pain threshold

Key Points

• Exposure to whole-body vibration did not effectively manage delayed-onset muscle soreness after high-intensity exercise in healthy, recreationally trained women.
• Researchers should study treatments to alleviate muscle pain in various populations.

Novel eccentric muscle contractions have been shown to cause exercise-induced muscle damage (EIMD). This damage typically results in decreased force production,^1,2 z-line streaming of sarcomeres,^3,4 delayed-onset muscle soreness (DOMS) and pain, edema,^5,6 and increased muscle tension, resulting in decreased range of motion (ROM).^5,6 Evidence has suggested that DOMS may result from sensitization of group III and IV afferent nociceptors by a host of inflammatory mediators⁷ and from large-fiber mechanoreceptors (ie, muscle spindles and tendon organs).^8,9 Researchers have reported that EIMD and DOMS lead to disability,¹⁰ impair daily activities,^11,12 and promote self-care behaviors similar to those of patients with pain observed and measured in the clinical setting (ie, clinical pain).^11,12 Pain and disability after exercise also have been reported as barriers to exercise¹³; consequently, limiting the deleterious effects of EIMD could improve exercise adherence.Prophylactic and therapeutic modalities (eg, massage, cryotherapy, stretching, ultrasound, electrical stimulation, anti-inflammatory drugs) designed to reduce DOMS have been studied widely,¹⁴ with most interventions demonstrating limited efficacy. Vibration is a modality that has shown efficacy in the treatment of chronic musculoskeletal pain,^15,16 suggesting promise for the treatment of DOMS as well. Whereas the effects of vibration on muscle pain from DOMS have not been widely studied, inconsistent and conflicting results have been reported. Local vibration applied directly to a damaged muscle has been reported to lead to heightened pain sensitivity, as evidenced by reduced pressure-pain thresholds (PPTs),^8,9,17 likely due to central sensitization of large-fiber mechanoreceptors. Conversely, prophylactic^18,19 application of whole-body vibration (WBV) before eccentric exercise and therapeutic application of both direct^20,21 and WBV plus stretching²² have been shown to reduce perceived levels of pain after EIMD.When applying a single 1-minute bout of 35-Hz WBV before eccentric exercise, Aminian-Far et al¹⁸ demonstrated pronounced attenuation of pain during movement and PPTs in the days after EIMD. However, it is unclear from their results if the vibration protocol attenuated pain per se or if vibration before eccentric exercise reduced the subsequent EIMD as evidenced by the markedly smaller decline in force-production ROM. Thus, we hypothesized that applying WBV after a high-intensity exercise may help decrease DOMS. Therefore, the purpose of this study was to investigate the effects of short-term WBV on DOMS over a 72-hour period after a high-intensity exercise protocol.     

Strength Training and Shoulder Proprioception

Context:

Proprioception is essential to motor control and joint stability during daily and sport activities. Recent studies demonstrated that athletes have better joint position sense (JPS) when compared with controls matched for age, suggesting that physical training could have an effect on proprioception.

Objective:

To evaluate the result of an 8-week strength-training program on shoulder JPS and to verify whether using training intensities that are the same or divergent for the shoulder''s dynamic-stabilizer muscles promote different effects on JPS.

Design:

Randomized controlled clinical trial.

Setting:

We evaluated JPS in a research laboratory and conducted training in a gymnasium.

Patients or Other Participants:

A total of 90 men, right handed and asymptomatic, with no history of any type of injury or shoulder instability.

Intervention(s):

For 8 weeks, the participants performed the strength-training program 3 sessions per week. We used 4 exercises (bench press, lat pull down, shoulder press, and seated row), with 2 sets each.

Main Outcome Measure(s):

We measured shoulder JPS acuity by calculating the absolute error.

Results:

We found an interaction between group and time. To examine the interaction, we conducted two 1-way analyses of variance comparing groups at each time. The groups did not differ at pretraining; however, a difference among groups was noted posttraining.

Conclusions:

Strength training using exercises at the same intensity produced an improvement in JPS compared with exercises of varying intensity, suggesting that the former resulted in improvements in the sensitivity of muscle spindles and, hence, better neuromuscular control in the shoulder.Key Words: joint position sense, neuromuscular control, muscle spindles

Key Points

• Improvements in joint position sense can be attained via standard strength-training exercises.
• Performing resistance exercises at consistent intensity rather than varying intensity resulted in better proprioception performance.

Improving muscle strength for joint stability is a goal of physical training for the shoulder.^1–3 According to Myers and Lephart,⁴ the rotator cuff, deltoid, biceps, teres major, latissimus dorsi, and pectoralis major muscles are responsible for providing shoulder stabilization. Inman et al⁵ were the first to state that the coactivation force of the shoulder''s dynamic stabilizers provides the joint stability. However, joint mechanics and stability may be compromised if such forces are not equalized. Therefore, in order to achieve joint stability, training must be directed at attaining proportional strength around the joint. Two main aspects should be taken into account during strength training: a specific muscle-force level and the force balance among muscles that act on the same joint.^3,6Shoulder-joint stability is the result of passive and dynamic components.⁷ The bone geometry, relative intra-articular pressure, glenohumeral labrum, and capsuloligamentous structures are passive components,⁴ whereas dynamic components are provided by contractile muscle activity coordinated around the joint and modulated by the neuromuscular system.⁸ The basis of passive and dynamic interactions is the proprioceptive information emerging from mechanoreceptors in muscles, tendons, joint-capsule ligaments, and skin, which are centrally integrated.^7,9 In this context, kinesthesia, joint position, and force sense are described as proprioception submodalities.^4,10–12Proprioception is essential to motor control and joint stability during daily activities and sports practice.^10,11 Thus, proprioception can be defined as the ability to recognize and to locate the body in relation to its position and orientation in space.^13,14 Allegrucci et al¹⁵ identified kinesthetic deficits in the dominant shoulder of throwing athletes as a mechanism for shoulder instability. The same result was found by Safran et al.¹⁶ Conversely, a recent study¹⁷ demonstrated that athletes have better joint position sense (JPS) than controls matched for age, suggesting that sport activity could have an effect on proprioception. Despite this result, the effect of strength training on proprioception remains unclear, although some authors^17–20 have described the effects of muscle strengthening on proprioception. These researchers hypothesized that strength training directly affects the functional capacity of the dynamic stabilizers. For this reason, it is important to understand the effects of this training on proprioception so that we can improve the strength-training protocols to increase joint stability.However, the effects of different strength-training programs on the JPS of healthy individuals remain debatable. Therefore, the focus of our study was to (1) evaluate the effect of 8 weeks of strength training on shoulder JPS and (2) verify whether using the same or divergent training intensities for the shoulder muscles'' stability produced any significant effects on JPS. We hypothesized that the JPS would be improved by strength training and that different strategies to control training intensity would promote different responses with regard to shoulder proprioception.     

Muscle Reaction Time During a Simulated Lateral Ankle Sprain After Wet-Ice Application or Cold-Water Immersion

Context

Cryotherapy is used widely in sport and exercise medicine to manage acute injuries and facilitate rehabilitation. The analgesic effects of cryotherapy are well established; however, a potential caveat is that cooling tissue negatively affects neuromuscular control through delayed muscle reaction time. This topic is important to investigate because athletes often return to exercise, rehabilitation, or competitive activity immediately or shortly after cryotherapy.

Objective

To compare the effects of wet-ice application, cold-water immersion, and an untreated control condition on peroneus longus and tibialis anterior muscle reaction time during a simulated lateral ankle sprain.

Design

Randomized controlled clinical trial.

Setting

University of Hertfordshire human performance laboratory.

Patients or Other Participants

A total of 54 physically active individuals (age = 20.1 ± 1.5 years, height = 1.7 ± 0.07 m, mass = 66.7 ± 5.4 kg) who had no injury or history of ankle sprain.

Intervention(s)

Wet-ice application, cold-water immersion, or an untreated control condition applied to the ankle for 10 minutes.

Main Outcome Measure(s)

Muscle reaction time and muscle amplitude of the peroneus longus and tibialis anterior in response to a simulated lateral ankle sprain were calculated. The ankle-sprain simulation incorporated a combined inversion and plantar-flexion movement.

Results

We observed no change in muscle reaction time or muscle amplitude after cryotherapy for either the peroneus longus or tibialis anterior (P > .05).

Conclusions

Ten minutes of joint cooling did not adversely affect muscle reaction time or muscle amplitude in response to a simulated lateral ankle sprain. These findings suggested that athletes can safely return to sporting activity immediately after icing. Further evidence showed that ice can be applied before ankle rehabilitation without adversely affecting dynamic neuromuscular control. Investigation in patients with acute ankle sprains is warranted to assess the clinical applicability of these interventions.Key Words: cryotherapy, neuromuscular control, proprioception, tilt platform

Key Points

• Ten minutes of joint cooling with wet-ice application or cold-water immersion did not adversely affect muscle reaction time or muscle amplitude in response to a simulated lateral ankle sprain.
• Athletes can return safely to sporting activity immediately after 10 minutes of ankle-joint cooling.
• Ice can be applied before ankle rehabilitation without adversely affecting dynamic control.

Ankle sprains occur frequently during sport and exercise.^1,2 In recent reviews of epidemiologic studies spanning more than 70 sports, authors^3,4 have identified ligament damage as responsible for 84% of all ankle injuries, with most involving the lateral ligament complex. The most commonly reported mechanism for an ankle sprain was excessive loading with the foot in plantar flexion and inversion.⁵Ankle-joint stability is achieved through the interaction of passive and dynamic systems. The lateral ligaments and joint capsule provide a passive restraint against external forces.⁵ These structures also contain mechanoreceptors that sense extreme or sudden movements and initiate a dynamic restraint^6,7; peroneus longus activation provides a dynamic restraint against excessive inversion,^5,8,9 whereas the tibialis anterior restrains excessive plantar flexion.^10–12 Coordinated and correctly timed contraction of these muscles is vital to protect the ankle joint against excessive movement.¹³ Individuals with functional ankle instability exhibit a delay in muscle reaction time, which may explain the frequent episodes of giving way and repetitive inversion injury commonly reported within this population.^11,14,15Cryotherapy is used widely in sport and exercise medicine.^16–19 It has an immediate analgesic effect^20–22 achieved through a range of physiologic mechanisms, including prolonged latency and duration of sensory action potentials, decreased nerve transmission,²³ suppression of nociceptive receptor sensitivity,²⁴ and counterirritant effects.²² These effects are often used to manage acute pain after soft tissue injury; ice application on the sidelines or during half time can provide cold-induced analgesia to facilitate a return to competitive activity. A growing trend is to use cold-induced analgesia to enhance rehabilitation and therapeutic exercise, which is often called cryokinetics.²⁵ Cryokinetic treatments are commonly 5 to 10 minutes in duration and involve cold-water immersion.^18,26,27 The basic premise is that cold-induced analgesia facilitates rehabilitation and enables exercises to be performed earlier than would normally be possible.^16,18In addition to providing effective pain relief, local cooling can induce a range of concomitant physiologic effects. In a recent review, Bleakley et al²⁸ provided consistent evidence that longer periods of ice application (>20 minutes) adversely affected strength, speed, power, and agility-based running. Another concern is that cooling tissue negatively affects neuromuscular control through changes in joint position sense²⁹ and delayed reaction time. Authors^13,25,30 of only 3 studies have assessed the effect of ice application on muscle reaction time during a simulated lateral ankle sprain. Although they all identified no change postapplication, these conclusions were limited to the effects of dry ice (crushed ice contained within a nonporous bag) on peroneus longus activity. Therefore, determining the effect of other popular modes of cooling on muscle reaction time is important. We also need to determine whether these patterns are consistent across other muscle groups contributing to dynamic ankle stability. Thus, the purpose of our study was to examine the effects of cryotherapy on muscle reaction time during a simulated lateral ankle sprain. Our specific objectives were to compare the effects of wet-ice application, cold-water immersion, and an untreated control condition on muscle reaction time of the peroneus longus and tibialis anterior muscle groups.     

Sport-Specific Training Targeting the Proximal Segments and Throwing Velocity in Collegiate Throwing Athletes

Context

The ability to generate, absorb, and transmit forces through the proximal segments of the pelvis, spine, and trunk has been proposed to influence sport performance, yet traditional training techniques targeting the proximal segments have had limited success improving sport-specific performance.

Objective

To investigate the effects of a traditional endurance-training program and a sport-specific power-training program targeting the muscles that support the proximal segments and throwing velocity.

Design

Randomized controlled clinical trial.

Setting

University research laboratory and gymnasium.

Patients or Other Participants

A total of 46 (age = 20 ± 1.3 years, height = 175.7 ± 8.7 cm) healthy National Collegiate Athletic Association Division III female softball (n = 17) and male baseball (n = 29) players.

Intervention(s)

Blocked stratification for sex and position was used to randomly assign participants to 1 of 2 training groups for 7 weeks: a traditional endurance-training group (ET group; n = 21) or a power-stability–training group (PS group; n = 25).

Mean Outcome Measure(s)

The change score in peak throwing velocity (km/h) normalized for body weight (BW; kilograms) and change score in tests that challenge the muscles of the proximal segments normalized for BW (kilograms). We used 2-tailed independent-samples t tests to compare differences between the change scores.

Results

The peak throwing velocity (ET group = 0.01 ± 0.1 km/h/kg of BW, PS group = 0.08 ± 0.03 km/h/kg of BW; P < .001) and muscle power outputs for the chop (ET group = 0.22 ± 0.91 W/kg of BW, PS group = 1.3 ± 0.91 W/kg of BW; P < .001) and lift (ET group = 0.59 ± 0.67 W/kg of BW, PS group = 1.4 ± 0.87 W/kg of BW; P < .001) tests were higher at postintervention in the PT than in the ET group.

Conclusions

An improvement in throwing velocity occurred simultaneously with measures of muscular endurance and power after a sport-specific training regimen targeting the proximal segments.Key Words: spine, trunk, pelvis-stability exercise training, performance assessment

Key Points

• Simultaneous improvements occurred in throwing velocity and power assessments of the chop and lift maneuvers.
• Training techniques for the proximal segments should aim to provide sport-specific stimuli.
• Assessment of the proximal segments should consider measuring the muscular-endurance, -strength, and -power characteristics of sport.

The synergistic muscle activity of the spine, pelvis, and trunk has been proposed to improve sport performance.¹ In anticipation of movement, the neurologic feed-forward mechanism activates the muscles that stabilize the intervertebral segments of the lumbar spine.² Regardless of the task, the rigid muscular support of the lumbar column provides a proximal base for the muscles of the pelvis and trunk to generate, absorb, and transfer forces throughout the kinetic chain.^1,3,4 Proximal synergy among the spine, pelvis, and trunk enables ground reaction forces to be converted into high-velocity movements at the extremities, such as those seen in throwing.⁵ Therefore, several authors^1,3,6–8 have proposed that sport-performance training and assessment techniques should attempt to target the endurance, strength, or power muscle characteristics of the proximal segments specific to sport. However, current training interventions and assessment practices have been unable to account for the sport-specific contributions of the proximal muscles and their effects on improvements in sport performance.Improvements in muscular endurance, strength, and electromyographic (EMG) activation relative to the muscles that support the spine, pelvis, and trunk are well documented after training interventions.^4,9–11 However, these claims have often been supported by studies in which researchers did not use comprehensive techniques that account for improvements to the muscular-endurance, strength, and power characteristics specific to the proximal stabilizers and the sport.^4,9,12 In many studies,^8,13–15 authors have not provided data to support the finding that improvements in sport are related to improvements in the proximal segments. Myer et al¹² reported improvements in pelvic and trunk stability after a training program specific to the hip and trunk. They concluded that the stability changes could translate into improved performance for sport and injury reduction; however, no sport-performance measures were provided to accompany the stability improvements.¹² Instead, authors have reported that training interventions improved sport performance measures without adequately monitoring change at the proximal segments.^8,13–15 Saeterbakken et al⁸ reported a 4.9% increase in throwing velocity after a 6-week sling-suspension training program involving unstable surfaces and closed kinetic chain movements. Seiler et al¹⁴ used a similar intervention and reported improvements in golf club velocity among junior golfers, whereas Sato and Mokha¹³ reported improvements in a 5000-m run after an unstable stability-ball strength-training program in middle-aged recreational runners. However, discerning a cause-and-effect relationship is difficult because they did not account for simultaneous improvements in sport performance and the musculature that supports the proximal segments.Researchers reporting improvements in the proximal-segment musculature have often noted no effect for sport performance, likely because of the commonly used uniplanar and isometric stability interventions and assessment techniques, such as plank maneuvers.^16–18 Isometric muscular endurance seems to be warranted, regardless of the sport, because of its role in providing stability at the spine in anticipation of movement.^2,19,20 However, investigators have hypothesized that strength and power movements are generated and transferred via the muscles that support the pelvis and trunk.¹ The literature supports this claim, as muscular-endurance training of the proximal stabilizers has been reported to improve muscular endurance and not explosive muscular power.^6,9 Thus, several authors have reported improvements in isometric endurance tests (P < .05) but not explosive field tests or sport performance after isometric-training interventions.^{16–18,21,22} To date, Stray-Pedersen et al²³ are the only authors to report improvements at the proximal segments as measured by an isometric hip-abduction test (P < .01) and ball velocity for a nonapproach soccer kick (P = .04) after a limb-suspension intervention training program.²³ However, the isometric hip-abduction assessment test used to evaluate the proximal segments has not been validated in the literature, and this test did not evaluate muscle power specific to the act of kicking.²³It seems reasonable to consider training and testing the proximal segments with stimuli that account for the muscular demands (endurance, strength, power) specific to sport rather than incorporating stimuli that target only the endurance capacity of the muscle. Monitoring the muscular-endurance, -strength, or -power demands of the proximal segments may be more appropriate for interpreting how training the proximal segments can influence sport. Sports that require more power movements, such as throwing or hitting, would require more strength and power training than endurance events, such as distance running. Therefore, the purpose of our study was to examine the effect of power training and endurance training on the muscles that support the proximal segments and on throwing velocity among National Collegiate Athletic Association Division III softball and baseball players. We hypothesized that a 7-week, sport-specific training intervention targeting muscular power would improve the sport-specific muscle contributions of the proximal segments and result in a faster throwing velocity compared with a traditional muscular-endurance training protocol.     

Increased Ligament Thickness in Previously Sprained Ankles as Measured by Musculoskeletal Ultrasound

Context:Lateral ankle sprains are among the most common injuries in sport, with the anterior talofibular ligament (ATFL) most susceptible to damage. Although we understand that after a sprain, scar tissue forms within the ligament, little is known about the morphologic changes in a ligament after injury.Objective:To examine whether morphologic differences exist in the thickness of the ATFL in healthy, coper, and unstable-ankle groups.Design:Cross-sectional study.Setting:Laboratory.Results:A group-by-limb interaction was evident (P = .038). The ATFLs of the injured limb for the coper group (2.20 ± 0.47 mm) and the injured limb for the unstable group (2.28 ± 0.53 mm) were thicker than the ATFL of the “injured” limb of the healthy group (1.95 ± 0.29 mm) at P = .015 and P = .015, respectively. No differences were seen in the uninjured limbs among groups.Conclusions:Because ATFL thicknesses of the healthy group''s uninjured ankles were similar, we contend that lasting morphologic changes occurred in those with a previous injury to the ankle. Similar differences were seen between the injured limbs of the coper and unstable groups, so there must be another explanation for the sensations of instability and the reinjuries in the unstable group.Key Words: ankle instability, anterior talofibular ligament, morphology

Key Points

• The anterior talofibular ligament can be viewed using musculoskeletal ultrasound imaging.
• The anterior talofibular ligaments of previously sprained ankles were thicker than those of uninjured ankles.
• Although coper ankles were more functionally similar to healthy ankles than to unstable ankles, they were structurally different. Only further research can determine the relationship between ligament damage and functional stability of the ankle.

Musculoskeletal ultrasound (MSUS) imaging is a new technique being used in the sports medicine setting. Compared with other imaging techniques, such as radiographic or magnetic resonance imaging (MRI), MSUS offers a safer, more time-efficient, and more cost-effective alternative. A real-time image can be captured via MSUS by using a transducer to send high-frequency sound waves into the body and recording the echo of the sound waves reflecting back, providing an image of the internal structure.^1,2 This method has been found to be effective in imaging upper extremity, lower extremity, and joint injuries.^1,3,4Oae et al³ reported greater than 90% accuracy for both MSUS and MRI in identifying injuries to the ankle. Lateral ankle sprains (LASs) are among the most common injuries in sport.⁵ An estimated 850 000 new ankle sprains occur each year in the United States,⁷ which does not include a 70% reinjury rate at the ankle.⁶ Ankle stability plays an important role in injury prevention. Passive stability of the ankle is predominantly the responsibility of ligaments supporting the bony structure of the talocrural joint because there are no musculotendinous insertions on the talus. Ligaments supporting the lateral complex of the ankle include the anterior talofibular ligament (ATFL), calcaneofibular ligament, and posterior talofibular ligament. The ATFL is a flat ligament that attaches from the anterior border of the lateral malleolus to the talus, just anterior to the lateral malleolus articular surface.⁸ The ATFL limits plantar flexion and inversion, motions that coincide with the most common mechanism of injury.⁸ As a result, the ATFL becomes vulnerable in a plantar-flexed and inverted position and is most susceptible to damage during an LAS.^5,6,9 An isolated tear of the ATFL occurs in about 80% of LASs.^10,11After an LAS, the fibrous structure of an ankle ligament is often disrupted by severe damage. Using MRI, Takao et al¹² reported visible scarring of the ATFL after injury. Using MSUS, McCarthy et al¹³ described a thickened ATFL, osseous spurs, and synovitic lesions after injury. Thickness values for the ATFL have been derived primarily from cadaveric studies^14,15; however, MRI-based in vivo studies demonstrated thickness of the ATFL to be in the range of 2 to 3 mm.^16,17 An abnormal ligament could affect the stabilizing properties of the ligament. In animal studies, although scar tissue formed within a ligament after injury, the newly scarred ligament allowed normal movement; however, the load capacity of that ligament was decreased by 60%.^18–20 Therefore, the strength of a ligament can be sufficient for active movement and injury rehabilitation soon after injury, but the decrease in load capacity of the scarred ligament may affect its stabilizing properties.Despite medical treatment and postinjury rehabilitation, more than 50% of individuals who sustain a moderate or severe ankle sprain experience some degree of residual disability and impairment due to symptoms such as pain, instability, loss of range of motion, and edema.^6,21 Those who do not fully recover from their ankle sprain often develop chronic ankle instability (CAI), which limits function not only in sport but also in activities of daily living. Patients with CAI typically complain of the ankle “giving way” or of repeated ankle sprains under seemingly low-risk conditions.²²Typically, CAI researchers have categorized participants into 2 groups: those with ankle instability (unstable) and those without ankle instability (healthy). The unstable group consists of individuals who experience recurrent sprains, sensations of instability, or both. Unfortunately, this method of grouping ignores those who sustained an ankle sprain but did not experience recurrent sprains or sensations of instability. In general, an ankle “coper” refers to an individual who has experienced an initial ankle sprain but not a subsequent sprain.²³ Only recently have copers been addressed in ankle-instability research.^24–29 Because copers are still a new cohort in this research, the classification of ankle copers differs somewhat among researchers.^25,28Although we understand that the fibrous nature of a ligament is disrupted after an LAS, little is known about the actual morphologic changes in a ligament. Therefore, the purpose of our study, using a mixed-model analysis, was to determine whether MSUS can be used to see differences in ligament thickness between the uninjured limb and the injured limb among the healthy, coper, and unstable groups. We hypothesized that the ligaments of the previously injured ankles would be thicker than the uninjured ankles.     

Correlation of Shoulder and Elbow Kinetics With Ball Velocity in Collegiate Baseball Pitchers

Context

Throwing a baseball is a dynamic and violent act that places large magnitudes of stress on the shoulder and elbow. Specific injuries at the elbow and glenohumeral joints have been linked to several kinetic variables throughout the throwing motion. However, very little research has directly examined the relationship between these kinetic variables and ball velocity.

Objective

To examine the correlation of peak ball velocity with elbow-valgus torque, shoulder external-rotation torque, and shoulder-distraction force in a group of collegiate baseball pitchers.

Design

Cross-sectional study.

Setting

Motion-analysis laboratory.

Patients or Other Participants

Sixty-seven asymptomatic National Collegiate Athletic Association Division I baseball pitchers (age = 19.5 ± 1.2 years, height = 186.2 ± 5.7 cm, mass = 86.7 ± 7.0 kg; 48 right handed, 19 left handed).

Main Outcome Measure(s)

We measured peak ball velocity using a radar gun and shoulder and elbow kinetics of the throwing arm using 8 electronically synchronized, high-speed digital cameras. We placed 26 reflective markers on anatomical landmarks of each participant to track 3-dimensional coordinate data. The average data from the 3 highest-velocity fastballs thrown for strikes were used for data analysis. We calculated a Pearson correlation coefficient to determine the associations between ball velocity and peak elbow-valgus torque, shoulder-distraction force, and shoulder external-rotation torque (P < .05).

Results

A weak positive correlation was found between ball velocity and shoulder-distraction force (r = 0.257; 95% confidence interval [CI] = 0.02, 0.47; r² = 0.066; P = .018). However, no significant correlations were noted between ball velocity and elbow-valgus torque (r = 0.199; 95% CI = −0.043, 0.419; r² = 0.040; P = .053) or shoulder external-rotation torque (r = 0.097; 95% CI = −0.147, 0.329; r² = 0.009; P = .217).

Conclusions

Although a weak positive correlation was present between ball velocity and shoulder-distraction force, no significant association was seen between ball velocity and elbow-valgus torque or shoulder external-rotation torque. Therefore, other factors, such as improper pitching mechanics, may contribute more to increases in joint kinetics than peak ball velocity.Key Words: throwing athletes, upper extremity, torque, force

Key Points

• A weak positive correlation was observed between ball velocity and shoulder-distraction force.
• No association was noted between ball velocity and elbow-valgus torque or shoulder external-rotation torque.
• Improper pitching mechanics may contribute more than ball velocity to increases in joint kinetics.

Injury rates among baseball pitchers at all levels of competition are on the rise, and the elbow and shoulder are the most commonly injured joints.^1–4 With approximately 27 000 to 45 000 collegiate players and more than 4.5 million total participants in organized baseball in the United States each year, finding ways to reduce the incidence of injury should be a primary objective of sports medicine professionals working with baseball players.^5–7Specific injuries at the elbow and glenohumeral joints have been linked to several kinetic variables during the throwing motion. Medial elbow injuries, such as ulnar collateral ligament sprains, are often caused by excessive elbow valgus and shoulder external-rotation torques occurring during the late cocking phase of throwing.^8–16 At the glenohumeral joint, that external-rotation torque during the late cocking phase and distraction forces during the deceleration phase are theorized to contribute to tears of the labrum.^9,11,17,18 Additionally, the peak distraction force generated during the arm-deceleration phase may contribute to rotator cuff injuries.^{9,11,17,19–22}Previous researchers have linked elbow and shoulder injuries to a variety of risk factors, including pitch volume,^23,24 increased innings pitched in a calendar year,^23,25 increased body mass,²³ pitch type,^24,26,27 and number of months pitched per year.²³ More recently, ball velocity has been examined as a possible risk factor for injury.^{10,23,28–30} Increased ball velocity has been identified as a risk factor for elbow and shoulder injury in adolescent pitchers²⁷ and for elbow injury in professional baseball pitchers.^23,28 Hurd et al²⁹ found a positive association between pitch velocity and elbow-varus moments in a group of high school pitchers. However, this was a nonelite sample of pitchers, and no authors have directly examined the relationship between ball velocity and the kinetic variables that have been implicated as contributing to injuries at the elbow and shoulder in pitchers at higher levels of competition. A strong association between ball velocity and joint kinetics might indicate that throwing at higher velocities puts more stress on joints, and, as a result, participants who throw at higher velocities are at an increased risk for injury. However, no association between ball velocity and joint kinetics would indicate that other variables besides ball velocity could be manipulated to alter joint kinetics and reduce injuries. Therefore, the purpose of our study was to examine the correlation of ball velocity with elbow-valgus torque, shoulder-distraction force, and shoulder external-rotation torque in a group of National Collegiate Athletic Association (NCAA) Division I collegiate baseball pitchers. Our hypothesis was that ball velocity would have a moderate positive correlation with elbow-valgus torque, shoulder-distraction force, and shoulder external-rotation torque.