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.     

Recovery After High-Intensity Intermittent Exercise in Elite Soccer Players Using VEINOPLUS Sport Technology for Blood-Flow Stimulation

Context

Electric muscle stimulation has been suggested to enhance recovery after exhaustive exercise by inducing an increase in blood flow to the stimulated area. Previous studies have failed to support this hypothesis. We hypothesized that the lack of effect shown in previous studies could be attributed to the technique or device used.

Objective

To investigate the effectiveness of a recovery intervention using an electric blood-flow stimulator on anaerobic performance and muscle damage in professional soccer players after intermittent, exhaustive exercise.

Design

Randomized controlled clinical trial.

Setting

National Institute of Sport, Expertise, and Performance (INSEP).

Patients or Other Participants

Twenty-six healthy professional male soccer players.

Intervention(s)

The athletes performed an intermittent fatiguing exercise followed by a 1-hour recovery period, either passive or using an electric blood-flow stimulator (VEINOPLUS). Participants were randomly assigned to a group before the experiment started.

Main Outcome Measures(s)

Performances during a 30-second all-out exercise test, maximal vertical countermovement jump, and maximal voluntary contraction of the knee extensor muscles were measured at rest, immediately after the exercise, and 1 hour and 24 hours later. Muscle enzymes indicating muscle damage (creatine kinase, lactate dehydrogenase) and hematologic profiles were analyzed before and 1 hour and 24 hours after the intermittent fatigue exercise.

Results

The electric-stimulation group had better 30-second all-out performances at 1 hour after exercise (P = .03) in comparison with the passive-recovery group. However, no differences were observed in muscle damage markers, maximal vertical countermovement jump, or maximal voluntary contraction between groups (P > .05).

Conclusions

Compared with passive recovery, electric stimulation using this blood-flow stimulator improved anaerobic performance at 1 hour postintervention. No changes in muscle damage markers or maximal voluntary contraction were detected. These responses may be considered beneficial for athletes engaged in sports with successive rounds interspersed with short, passive recovery periods.Key Words: calf muscle, fatigue, athletes

Key Points

• After intermittent fatiguing exercise, these elite male soccer players showed better restoration of anaerobic performance with blood-flow stimulation than with passive recovery at 1 hour.
• Neither modality improved clearance of muscle damage markers or maximal voluntary contraction.

Rapid recovery of performance is important for elite athletes engaged in intermittent exercise that involves periods of intense exercise interspersed with short recovery periods (eg, martial arts, ice hockey, field sports). Optimizing training recovery may also be beneficial for performing successive bouts of training or competition over a season without associated fatigue or overtraining effects.The inability to repeat the same level of performance in short-duration exercise is frequently attributed to peripheral fatigue involving metabolite accumulation and muscle damage^1,2 resulting from mechanical stress, imbalances in muscle cell homeostasis, or local inflammation from exercise.³ Indeed, the response of different muscle enzymes (mainly creatine kinase [CK] and lactate dehydrogenase [LDH]) has received researchers'' attention because strenuous exercise induces muscle cell structural damage, which results in increased plasma concentrations of muscle enzymes such as CK and LDH.⁴ The efflux of CK and LDH proteins from muscle may be attributed to increased permeability of the plasma membrane or intramuscular vasculature (or both).⁵ Thus, a reduction in these markers has been proposed as an indicator of recovery after strenuous exercise that induces muscle damage.⁶ To optimize recovery, various techniques have been suggested to accelerate the clearance of muscular damage or metabolite accumulations. Usually, these techniques focus on local fatigue. Their main goal is to treat fatigue by directly applying the recovery method to the working muscles (eg, electromyostimulation, local cryotherapy, or cold-water immersion). This approach showed positive results after muscle damage by reducing local inflammation, especially when cold modalities were used.⁷ However, results on peripheral fatigue from metabolite accumulation are inconclusive, probably because the metabolic byproducts are released into the blood. From these findings, a change in the recovery approach from a local treatment to a systemic view was necessary. One possible way to achieve this goal is to improve the peripheral circulation and the venous return by stimulating total blood flow. In athletes, several techniques have been proposed to achieve this result. Of these, active recovery,^8,9 contrast water therapy,¹⁰ compression garments,¹¹ low-level laser therapy,¹² and low-frequency electromyostimulation¹³ have been investigated and compared with passive recovery (PAS).^6,14 The results of these studies provide no definitive consensus on the ability to improve explosive strength and anaerobic capacity performance or clear muscle damage markers after exercise.^15–17 Lattier et al¹⁸ showed no difference in neuromuscular function and maximal test performance after a recovery intervention using blood-flow stimulation from electromyostimulation compared with PAS or active recovery. Based on these observations, several authors concluded that the effects of these techniques are minimal, especially on performance. However, researchers^13,19 have hypothesized that this lack of effect could also be associated with the technique, the device used, or the localization of the electric stimulation (eg, systemic treatment [calf] versus local treatment [quadriceps]), suggesting that the blood flow and, more particularly, the venous return may not be effectively increased. Accordingly, Martin et al¹³ recommended optimizing the electric stimulation to better approximate the physiologic contraction of the muscle; a new way of using an electric muscle stimulator on the calf muscles could provide interesting results. This systemic approach is based on results showing that total blood flow can be efficiently stimulated by intensifying the pumping action associated with calf muscle contractions from techniques such as electromyostimulation, cuff inflation, or walking.²⁰ Indeed, these muscles, which have been termed the “peripheral venous heart,” “calf muscle pump,” and “musculovenous pump,” were responsible for 80% of the venous return^21–23 and considered a second heart. A low-intensity, repetitive mechanical contraction-relaxation muscle cycle may increase local and total blood flow, translocation, and removal of metabolites and reduce intracellular fluid volume.²⁴ However, using electric muscle stimulation to increase blood flow for exercise recovery has been ineffective despite the emergence of new devices that significantly improved total blood flow and venous return.^25–29 Therefore, we hypothesized that such a device applied to the calf muscles could result in faster restoration in performance and reduce the amount of muscle damage markers after fatiguing exercise.The purpose of our study was to investigate the effectiveness of muscle stimulation using the VEINOPLUS unit (Ad Rem Technology, Paris, France) on explosive strength and 30-second all-out performance and CK and LDH recovery profiles in professional soccer players after exhaustive intermittent exercise. We proposed that use of the VEINOPLUS would result in better restoration of anaerobic performance than passive recovery.     

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 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.     

What Can the First 2 Months Tell Us About Outcomes After Anterior Cruciate Ligament Reconstruction?

Context:

Substantial research has been conducted on anterior cruciate ligament reconstruction (ACLR) to evaluate patient outcomes. However, little attention has been given to outcomes during the early phase of recovery and how early deficits affect both short- and long-term outcomes.

Objective:

To identify relationships between demographic (age, sex, and body mass index [BMI]) and intraoperative (isolated ACLR versus primary ACLR + secondary procedures), and postoperative (range-of-motion [ROM] and peak isometric knee-extension force [PIF]) variables during the first 2 months after ACLR using self-reported outcomes.

Design:

Cohort study.

Setting:

Outpatient orthopaedic hospital.

Patients or Other Participants:

A total of 63 patients (38 men, 25 women; age = 33.0 ± 12.1 years; BMI = 26.3 ± 6.5 kg/m²) who underwent ACLR.

Main Outcome Measure(s):

Demographic, intraoperative, and postoperative variables were collected at 1 and 2 months after ACLR and were compared with International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form scores at 1, 2, and ≥12 months.

Results:

Significant relationships were identified between ≥12-month IKDC scores and the 1-month (Pearson correlation, r = 0.283, r² = 0.08; P = .025) and 2-month (r = 0.301, r² = 0.09; P = .017) IKDC scores. After controlling for other variables, we found that the PIF ratio measures at 1 and 2 months were positively associated with 1- and 2-month IKDC scores (P < .001) and BMI was negatively associated with both 1- and 2-month IKDC scores (P < .05). One-month IKDC scores were related to the 1-month difference in knee-flexion ROM (P = .04).

Conclusions:

The IKDC scores during the first 2 months were positively correlated with patients'' perceptions of function on long-term IKDC scores. It also appears that improvements in lower extremity strength and flexion ROM deficits were positively associated with short-term IKDC scores. Higher BMI was negatively associated with patients'' perceptions of function on short-term IKDC scores.Key Words: force output, knee, motion, rehabilitation, International Knee Documentation Committee

Key Points

• After anterior cruciate ligament reconstruction, patients'' subjective International Knee Documentation Committee (IKDC) scores at both 1- and 2-month follow-ups had fair but significantly positive associations with the ≥12-month IKDC score.
• The ratio of surgical- to nonsurgical-limb measures of peak isometric knee-extension force at 1 and 2 months was positively associated with 1- and 2-month IKDC scores.
• The difference in flexion range of motion between the surgical and nonsurgical limbs had a significant positive relationship with 1-month IKDC score.
• Body mass index had a significant negative association with both 1- and 2-month IKDC scores.
• No significant relationships were noted between demographic, intraoperative, or postoperative variables during the first 2 months and IKDC scores at ≥12 months after anterior cruciate ligament reconstruction.

Anterior cruciate ligament reconstruction (ACLR) is a commonly performed surgical procedure in active individuals; injury to this ligament is more frequent in sports requiring multidirectional activities, with an estimated incidence of 81 per 100 000 persons.^1–3 Discrepancies in the literature exist when evaluating the effects of surgical intervention and rehabilitation on postoperative outcomes. Reconstruction of this ligament and postoperative rehabilitation have been shown to be effective in restoring functional stability of the knee,⁴ minimizing the development of osteoarthritis (OA),^5,6 and returning patients to their previous level of function.^5,7 However, persistent lower extremity muscle weakness,^8,9 insufficient dynamic knee stability,¹⁰ and increased risk of posttraumatic arthrosis³ have also been reported. A considerable number of individuals are unable to return to competitive sports despite successful rehabilitation or ACLR with rehabilitation.¹¹ Though controversy lingers, substantial research has been conducted on specific surgical procedures, various graft options, and rehabilitation protocols in an attempt to identify prognostic risk factors and modifiable predictors to improve self-reported outcomes after ACLR.^12,13Although multiple authors have evaluated various factors related to returning individuals to their prior level of function, research identifying the effectiveness of early postoperative measures on self-reported outcomes after ACLR is lacking. Several self-efficacy studies have provided compelling evidence that a large number of patients are unable to return to their prior level of function in spite of an apparently successful surgery and rehabilitation.¹¹ Therefore, it is important to understand the psychosocial ramifications of the injury and monitor self-reported outcomes throughout the rehabilitation process to improve both short- and long-term function.Accumulating evidence suggests that both demographic and intraoperative findings have a significant influence on patient outcomes after ACLR.^5,14–20 In particular, medial meniscectomy, residual ligamentous laxity, and femoral chondral defects have all been associated with subsequent degenerative arthrosis as seen on radiography.^5,15,20 Studies also suggest that demographic risk factors such as age, sex, and body mass index (BMI) might have a profound influence on self-reported outcomes after ACLR. Higher BMI scores might predict lower self-reported outcomes scores.^12,13 Also, the odds of successful outcomes are 0.35 times lower for persons over the traditional threshold for obesity (BMI ≥ 30 kg/m²).²¹ Conflicting evidence exists on whether age and sex are associated with self-reported outcomes.^14,16–19 Whereas some studies^14,17,18 point to lower self-reported outcomes in women and older patients, others^16,19 indicate no difference in overall outcomes.Postoperative rehabilitation is an integral component to a successful recovery after ACLR. The inability to restore symmetric range of motion (ROM)^6,7 and muscular strength^7,22 affects patient satisfaction. Postoperative ROM deficits have been associated with a higher incidence of OA changes and lower self-reported outcomes scores.^5,6,19 Additional research has shown that muscular weakness, specifically of the quadriceps femoris, is related to poorer functional outcomes.^23–25 Furthermore, establishing preoperative lower extremity strength^7,22,26 and restoring symmetric ROM^6,7 are important in increasing overall functional ability and improving self-reported outcomes after ACLR.Although a significant body of literature has addressed the effects of demographic, intraoperative, and postoperative factors on long-term self-reported outcomes, little attention has been given to the association between these variables and outcomes during the early phase of recovery and how deficits affect long-term outcomes. Studies are needed to investigate correlations between clinical measures and self-reported outcomes during the early stages of recovery. Such studies will reveal the potentially important influences of these factors on both short- and long-term outcomes and will guide clinicians in making appropriate decisions regarding early-stage postoperative rehabilitation.The purpose of our study was to identify relationships between demographic (age, sex, BMI), intraoperative (isolated ACLR versus primary ACLR + secondary procedures), and postoperative (ROM and peak isometric knee-extension force [PIF]) variables during the first 2 months after ACLR and self-reported outcomes as measured by the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form at 1, 2, and ≥12 months. First, we hypothesized that deficits in ROM and PIF during the first 2 months after surgery would be positively associated with IKDC scores at the equivalent time points and at ≥12 months postoperatively. Second, we proposed that IKDC scores during the first 2 months after surgery would be positively associated with IKDC scores at ≥12 months. Third, we suggested that participant characteristics such as secondary surgical procedures, age, sex, and BMI would have significant influences on IKDC scores at 1, 2, and ≥12 months after ACLR.     

Ankle Dorsiflexion Among Healthy Men With Different Qualities of Lower Extremity Movement

Context:

Lower extremity movement patterns have been implicated as a risk factor for various knee disorders. Ankle-dorsiflexion (DF) range of motion (ROM) has previously been associated with a faulty movement pattern among healthy female participants.

Objective:

To determine the association between ankle DF ROM and the quality of lower extremity movement during the lateral step-down test among healthy male participants.

Design:

Cross-sectional study.

Setting:

Training facility of the Israel Defense Forces.

Patients or Other Participants:

Fifty-five healthy male Israeli military recruits (age = 19.7 ± 1.1 years, height = 175.4 ± 6.4 cm, mass = 72.0 ± 7.6 kg).

Intervention(s):

Dorsiflexion ROM was measured in weight-bearing and non–weight-bearing conditions using a fluid-filled inclinometer and a universal goniometer, respectively. Lower extremity movement pattern was assessed visually using the lateral step-down test and classified categorically as good or moderate. All measurements were performed bilaterally.

Main Outcome Measure(s):

Weight-bearing and non–weight-bearing DF ROM were more limited among participants with moderate quality of movement than in those with good quality of movement on the dominant side (P = .01 and P = .02 for weight-bearing and non–weight-bearing DF, respectively). Non–weight-bearing DF demonstrated a trend toward a decreased range among participants with moderate compared with participants with good quality of movement on the nondominant side (P = .03 [adjusted P = .025]). Weight-bearing DF was not different between participants with good and moderate movement patterns on the nondominant side (P = .10). Weight-bearing and non–weight-bearing ankle DF ROM correlated significantly with the quality of movement on both sides (P < .01 and P < .05 on the dominant and nondominant side, respectively).

Conclusions:

Ankle DF ROM was associated with quality of movement among healthy male participants. The association seemed weaker in males than in females.Key Words: anterior cruciate ligament, hip, knee, lateral step-down test, patellofemoral pain syndrome

Key Points

• Healthy males with a moderate quality of movement on the lateral step-down test exhibited less ankle-dorsiflexion range of motion than those with a good quality of movement.
• When a lower quality of movement is present in males, clinicians should consider interventions to increase ankle dorsiflexion.

An altered lower extremity movement pattern, consisting of excessive femoral adduction and internal rotation leading to excessive knee valgus alignment, has been implicated as a risk factor for patellofemoral pain syndrome (PFPS) and noncontact anterior cruciate ligament injuries.^1–3 Various factors have been suggested to contribute to an altered movement pattern, including decreased strength of the ipsilateral hip musculature,^4,5 increased subtalar joint pronation,^6,7 and altered motor control.⁸ Assessment of movement pattern and the factors associated with it is therefore commonly performed in the evaluation of patients with PFPS, as well as in screening for the risk of knee injury.^9–11Another possible contributor to an altered movement pattern is the available ipsilateral ankle-dorsiflexion (DF) range of motion (ROM). Decreased ankle DF ROM can limit the forward progression of the tibia over the talus during activities that require simultaneous knee flexion and ankle DF (eg, squatting, stair descent). A possible compensation for the limited motion of the tibia could be subtalar pronation, which may shift the tibia and the knee medially into greater valgus alignment.^6,12–14 Some evidence already exists for the association between ankle DF and the lower extremity movement pattern. Decreased DF has been previously associated with increased knee valgus during a drop-land maneuver,¹⁴ a squat,¹⁵ and a step-down maneuver¹⁶ among healthy participants.One limitation of the current literature regarding this topic is the inclusion of only female participants in many of the studies evaluating lower extremity movement patterns and the associated factors.^{4,6,14,16–18} This is likely because of sex differences in kinematics, kinetics, and muscle-activation patterns during various functional activities.^8,19,20 Women have been shown to perform activities such as cutting, jumping, and landing with greater knee valgus alignment and greater knee extension than men.^19,20 These differences are hypothesized to account for the greater incidence of noncontact anterior cruciate ligament tears and PFPS among women.^1,2,21,22 Accordingly, authors^14,16 of the 2 studies that have previously linked decreased ankle DF with a faulty movement pattern included only female participants as well. A third study of a mixed population demonstrated only a statistical trend for the association between ankle DF and a faulty movement pattern.¹⁵ It is therefore unclear whether the association between ankle DF and lower extremity movement pattern is similar for both sexes.Paradoxically, another limitation of the current literature is the use of sophisticated 3-D motion-analysis systems in many of the studies evaluating lower extremity movement patterns.^2,4,14,17,18 Although this type of analysis certainly contributes to a high level of precision and reliability, clinicians and coaches typically do not have the access, time, or skill to operate such systems. Instead, visual observation is often relied on to assess movement patterns in the clinic or on the field. It is unknown, however, to what extent any movement deviations identified during 3-D motion analyses correlate with movement deviations identified visually. Consequently, the findings from 3-D motion analyses studies may be difficult to apply in the clinical setting or on the field. We therefore decided to assess whether ankle DF ROM is related to the quality of lower extremity movement as assessed visually among healthy male participants.The lateral step-down (LSD) test is frequently used to assess movement patterns of the lower extremity.^9,11,23–25 Piva et al²⁵ suggested a visually based rating system for classifying the quality of movement during the LSD test. The reliability of this rating system has been established previously.^16,25 Our hypothesis was that male participants with a lower quality of movement on the LSD would exhibit less ankle DF ROM.     

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.     

Trunk and Lower Extremity Kinematics During Stair Descent in Women With or Without Patellofemoral Pain

Context

There is limited evidence indicating the contribution of trunk kinematics to patellofemoral pain (PFP). A better understanding of the interaction between trunk and lower extremity kinematics in this population may provide new avenues for interventions to treat PFP.

Objective

To compare trunk and lower extremity kinematics between participants with PFP and healthy controls during a stair-descent task.

Design

Cross-sectional study.

Setting

Research laboratory.

Patients or Other Participants

Twenty women with PFP (age = 22.2 ± 3.1 years, height = 164.5 ± 9.2 cm, mass = 63.5 ± 13.6 kg) and 20 healthy women (age = 21.0 ± 2.6 years, height = 164.5 ± 7.1 cm, mass = 63.8 ± 12.7 kg).

Intervention(s)

Kinematics were recorded as participants performed stair descent at a controlled velocity.

Main Outcome Measure(s)

Three-dimensional joint displacement of the trunk, hip, and knee during the stance phase of stair descent for the affected leg was measured using a 7-camera infrared optical motion-capture system. Pretest and posttest pain were assessed using a visual analogue scale. Kinematic differences between groups were determined using independent-samples t tests. A 2 × 2 mixed-model analysis of variance (group = PFP, control; time = pretest, posttest) was used to compare knee pain.

Results

We observed greater knee internal-rotation displacement for the PFP group (12.8° ± 7.2°) as compared with the control group (8.9° ± 4.4°). No other between-groups differences were observed for the trunk, hip, or other knee variables.

Conclusions

We observed no difference in trunk kinematics between groups but did note differences in knee internal-rotation displacement. These findings contribute to the current knowledge of altered movement in those with PFP and provide direction for exercise interventions.Key Words: anterior knee pain, knee internal rotation, neuromuscular control

Key Points

• Trunk kinematics did not differ between women with and without patellofemoral pain during stair descent.
• Women with patellofemoral pain demonstrated greater knee internal-rotation displacement during stair descent than women without patellofemoral pain.

Patellofemoral pain (PFP) is one of the most frequent chronic injuries among females.^1,2 The causes of PFP are multifactorial, with patellofemoral malalignment commonly accepted as a major contributor.^2,3 Patellofemoral malalignment increases contact pressure within the patellofemoral joint, leading to abnormal cartilage wear and ultimately degenerative changes if left untreated or if conservative treatment options fail.^4,5Lower extremity kinematics may directly influence patellofemoral contact pressure during dynamic tasks. Specifically, the motions of femoral internal rotation, femoral adduction, and knee valgus increase patellofemoral contact pressure.^3,6–8 Extensive research^3,6,9–13 has been conducted to determine alterations in lower extremity kinematics associated with PFP. Lower extremity kinematics may be influenced by other factors that, if recognized, may have a significant effect on treatment interventions for those with PFP.Although there is evidence that trunk kinematics influence lower extremity kinematics and loading,^14–16 few studies have examined trunk kinematics in participants with PFP.^17,18 The presence of aberrant trunk motion in those with PFP and its influence on lower extremity kinematics has been theorized.¹⁹ In the frontal plane specifically, it has been proposed that individuals with PFP who display hip-abductor weakness compensate by elevating the contralateral pelvis and leaning toward the stance limb. This trunk lean has the potential to alter the orientation of the ground reaction force and subsequent external moments acting on the knee in the frontal plane. In the sagittal plane, trunk flexion moves the ground reaction force vectors anteriorly to both the hip and knee joints, thereby increasing the demand of the hip extensors and decreasing the demand of the knee extensors. Decreasing the quadriceps demand decreases the compressive forces within the patellofemoral joint.¹⁹ Given that previous researchers^13,14,16 have demonstrated a relationship between trunk and lower extremity kinematics in a healthy population, it is plausible that individuals with PFP may have altered trunk kinematics that indirectly influence patellofemoral contact pressure.The primary purpose of our study was to compare trunk and lower extremity kinematics during stair descent between women with and without PFP. Our a priori hypotheses were that women with PFP would have greater trunk rotation and lateral flexion toward the stance leg and greater overall trunk flexion. Based on previously reported observations,^20–25 we also expected to observe greater hip adduction, hip internal rotation, and knee valgus in those with PFP.     

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.     

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.     

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.     

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.     

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?”     

Asymptomatic Elite Adolescent Tennis Players' Signs of Tendinosis in Their Dominant Shoulder Compared With Their Nondominant Shoulder

ContextTennis is an asymmetric overhead sport with specific muscle-activation patterns, especially eccentrically in the rotator cuff. Magnetic resonance imaging (MRI) findings in asymptomatic adolescent elite tennis players have not previously been reported.ObjectiveThe first aim of the study was to describe MRI findings regarding adaptations or abnormalities, as well as muscle cross-sectional area (CSA), of the rotator cuff. The second aim of the study was to investigate the rotator cuff based on the interpretation of the MRI scans as normal versus abnormal, with the subdivision based on the grade of tendinosis, and its association with eccentric rotator cuff strength in the dominant arm (DA) of the asymptomatic elite adolescent tennis player.SettingTesting environment at the radiology department of Medicinsk Röntgen AB.Intervention(s)We assessed MRI scans and measured the CSA of the rotator cuff muscle. The non-DA (NDA) was used as a control. In addition, eccentric testing of the external rotators of the DA was performed with a handheld dynamometer.ResultsThe DA and NDA displayed different frequencies of infraspinatus tendinosis (grade 1 changes) (P < .05). Rotator cuff measurements revealed larger infraspinatus and teres minor CSA (P < .05) in the DA than in the NDA. Mean eccentric external-rotation strength in the DA stratified by normal tendon and tendinosis was not different between groups (P = .723).ConclusionsAsymptomatic adolescent elite tennis players demonstrated infraspinatus tendinosis more frequently in the DA than in the NDA. Clinicians must recognize these tendon changes in order to modify conditioning and performance programs appropriately.Key Words: magnetic resonance imaging, adolescents, overhead athletes, tennis

Key Points

• Grade 1 tendinosis of the rotator cuff in the asymptomatic adolescent elite tennis player appeared almost exclusively in the dominant arm and more frequently in the infraspinatus tendon.
• Recognition of these early changes is important so that technical instructions, conditioning and performance programs, and exposure times can be modified to prevent progression to symptomatic rotator cuff problems.

The increasing demands required to enter the highest adult elite level in any sport necessitate enormous amounts of training during adolescence. Tennis is no exception and has become, from a physical perspective, one of the most challenging sports worldwide. In view of the early specialization that has become more common, the overall exposure time in tennis today is greater for adolescent players before they reach the professional level. This could possibly explain the frequent presence of overuse injuries, especially in the upper extremity.¹ Tennis is an asymmetric sport with specific muscle-activation patterns, especially eccentrically in the supraspinatus, infraspinatus (IS), and teres minor (TM) during the complex and rapid serving motion.² As a result of the large demands on joint mobility, muscle strength, and complex biomechanics in the shoulder girdle during overhead sport movements, sport-specific adaptations at the glenohumeral and scapulothoracic level may occur even during adolescence.^3,4 Radiologically detectable adaptations and abnormalities in asymptomatic athletes have previously been reported.⁵⁻⁷ Although findings such as these might not initially be associated with clinical symptoms, sports medicine professionals must recognize these changes to prevent progression into the continuum of symptomatic rotator cuff injury.Shoulder injuries occur often in overhead athletes at various levels of competition.⁸ Common shoulder injuries associated with repetitive throwing include tendinosis of the rotator cuff, glenohumeral instability, subluxation, and stress-related injury to the proximal humerus (also known as Little League shoulder).⁹Most shoulder injuries are thought to occur during the arm-cocking and arm-deceleration phases. In particular, the external rotators are highly loaded eccentrically during the deceleration phase by resisting shoulder internal rotation and horizontal adduction.^10,11 In specific sports, such as tennis, elite players without shoulder injury have demonstrated shoulder-rotation muscle-strength imbalances that alter the ratio among the rotator cuff muscles.¹² Although these differences do not seem to immediately affect athletic performance, decreased external-rotation strength has been identified as a risk factor for shoulder pain in overhead athletes.¹³ Therefore, detection and prevention with exercise programs at an early age are recommendedInternal impingement is one of the most common shoulder injuries seen in overhead athletes.^14,15 Walch et al¹⁶ were the first to describe posterosuperior impingement, referring to a specific position in the throwing motion, with the shoulder in 90° of abduction and maximal external rotation. In this position, the posterior fibers of the supraspinatus and anterior fibers of the IS come in contact between the humerus and the posterior superior labrum.^5,17 As these areas make contact, fraying of the undersurface of the supraspinatus and IS tendons can occur and cause injury.¹⁸ Although this adaptation might be physiologic, repeated throwing has been shown to lead to articular-side tears of the rotator cuff.^5,17 In an arthroscopic study of 41 symptomatic professional athletes, 93% had undersurface fraying of the rotator cuff tendons, thus supporting the theory of internal impingement as a factor in injury.¹⁹ Similar findings were reported by Walch et al¹⁶ in their study of 17 overhead athletes; 76% had evidence of undersurface rotator cuff tears. In addition, partial-thickness tears from tendon overload most often develop on the intra-articular side of the cuff and not on the bursal side.²⁰Magnetic resonance imaging (MRI) is a widely used, clinically relevant modality in the evaluation of the shoulder, especially when assessing the elite overhead athlete.^6,7,9,21,22 The aim of MRI is to identify injury; therefore, it is essential to investigate the spectrum of normal anatomic structures to accurately detect and characterize pathologic changes.^{6,7,9,17,21−23} Knowledge of overhead-throwing biomechanics is crucial to understanding specific injuries encountered on diagnostic imaging in throwing athletes.²⁴Miniaci et al⁷ used MRI to evaluate the supraspinatus and IS in both shoulders of asymptomatic professional baseball pitchers and showed no differences between the dominant arm (DA) and nondominant arm (NDA). However, Jost et al⁶ identified abnormal MRI findings in 93% of DA throwing shoulders; of these, only 37% were symptomatic. In addition, MRI evidence of rotator cuff abnormality was present in 40% of the throwing shoulders in young asymptomatic overhead athletes compared with none (0%) of the nonthrowing shoulders.⁵It is well established that muscle strength has a direct relationship with muscle cross-sectional area (CSA). Muscle CSA has been assessed for several reasons previously described in the literature, and MRI is considered the gold standard for in vivo estimation of muscle CSA.^25,26Starting a sport at an early age might lead to adaptive or abnormal changes, and the rotator cuff in asymptomatic adolescent elite tennis players should be evaluated, as has been done in baseball players.⁵ Strength, measured with a handheld dynamometer (HHD), has also been described in this population.²⁷To our knowledge, no study has been published describing MRI findings in the rotator cuff of asymptomatic adolescent elite tennis players or such findings in association with eccentric rotator cuff muscle strength assessed with an HHD. Therefore, the first aim of the study was to describe adaptations or abnormalities on MRI, as well as muscle CSA of the rotator cuff. The second aim was to investigate the rotator cuff based on the interpretation of the MRI scans as normal versus abnormal, with the subdivision based on the grade of tendinosis, and its association with eccentric rotator cuff strength in the DA of the asymptomatic elite adolescent tennis player.