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.     

Two- and 3-Dimensional Knee Valgus Are Reduced After an Exercise Intervention in Young Adults With Demonstrable Valgus During Squatting

Context:

Two-dimensional (or medial knee displacement [MKD]) and 3-dimensional (3D) knee valgus are theorized to contribute to anterior cruciate ligament injuries. However, whether these displacements can be improved in the double-legged squat (DLS) after an exercise intervention is unclear.

Objective:

To determine if MKD and 3D knee valgus are improved in a DLS after an exercise intervention.

Design:

 Randomized controlled clinical trial.

Setting:

Research laboratory.

Patients or Other Participants:

A total of 32 participants were enrolled in this study and were randomly assigned to the control (n = 16) or intervention (n = 16) group. During a DLS, all participants demonstrated knee valgus that was corrected with a heel lift.

Intervention(s):

 The intervention group completed 10 sessions of directed exercise that focused on hip and ankle strength and flexibility over a 2- to 3-week period.

Main Outcome Measure(s):

We assessed MKD and 3D knee valgus during the DLS using an electromagnetic tracking system. Hip strength and ankle-dorsiflexion range of motion were measured. Change scores were calculated for MKD and 3D valgus at 0%, 10%, 20%, 30%, 40%, and 50% phases, and group (2 levels)-by phase (6 levels) repeated-measures analyses of variance were conducted. Independent t tests were used to compare change scores in other variables (α < .05).

Results:

The MKD decreased from 20% to 50% of the DLS (P = .02) and 3D knee valgus improved from 30% to 50% of the squat phase (P = .001). Ankle-dorsiflexion range of motion (knee extended) increased in the intervention group (P = .009). No other significant findings were observed (P > .05).

Conclusions:

 The intervention reduced MKD and 3D knee valgus during a DLS. The intervention also increased ankle range of motion. Our inclusion criteria might have limited our ability to observe changes in hip strength.Key Words: movement analysis, screening, anterior cruciate ligament, dynamic knee valgus, dorsiflexion

Key Points

• A systemic corrective exercise program decreased 2- and 3-dimensional knee valgus and increased ankle-dorsiflexion flexibility during a double-legged squat.
• Hip-extension and -abduction strength increased after the exercise program, but the findings were not statistically significant.

Knee valgus is believed to be a major contributor to noncontact anterior cruciate ligament (ACL) injuries.¹ Three-dimensional (3D) assessment of knee-valgus angle (3D knee valgus) is considered the gold standard method of measurement; it is assessed via motion analysis and describes the relative relationship between the femur and tibia. However, 2-dimensional (2D) knee-valgus assessment methods are popular because of low cost, ease of implementation, and the ability to screen large numbers of participants.^2,3 Various methods of calculating 2D knee valgus have been reported in the literature and have been referred to as knee-separation distance, frontal-plane projection angle, and medial knee displacement (MKD).^2,4–6 All of these measurements assess frontal-plane knee motion and use combinations of standard video cameras, basic editing software, and motion analysis, depending on the measure of interest.Knee valgus results from a combination of femoral and tibial motions, which can be influenced by the joints proximal and distal to the knee, including the trunk, hip, and ankle.^7–11 Lack of femoral control can result in excessive adduction and internal rotation, which can stress the ACL.^10,12 However, the relationship between hip-muscle strength and frontal-plane knee motion is not as clear as one might expect.^5,8,13 For example, Thijs et al¹⁴ calculated 2D valgus angles during a lunge and observed no relationship between frontal-plane motion and hip-muscle strength. Norcross et al¹³ also observed no relationship between isometric or eccentric hip strength (hip abductor and external rotation) and 3D knee valgus during a lateral step-down test. Additionally, Bell et al⁹ concluded that their participants had adequate hip strength and range of motion (ROM) despite excessive MKD during a double-legged squat (DLS). Yet these findings contrast with those of other authors^4,15 who have observed relationships between hip strength and knee motion. Further research is needed to definitively describe the relationships between hip-muscle strength and frontal-plane knee motion.Foot pronation and limited ankle dorsiflexion are also believed to influence knee valgus.^7–9,12 Rabin and Kozol⁸ grouped individuals based on performance during a lateral step-down test. Females with worse movement quality (including knee position, pelvic position, and trunk movement) had restricted ankle-dorsiflexion motion as a result of gastrocnemius and soleus tightness. These results were similar to the findings of Bell et al,⁹ who examined hip and ankle strength and ROM based on movement during the DLS. Participants with visual knee valgus were compared with those who kept their knees over their toes during the DLS. The valgus group tended to have soleus-restricted ankle ROM. Thus, limited ankle dorsiflexion is believed to result in biomechanical compensations at the knee by increasing subtalar pronation and tibial abduction and internal rotation,¹² which are components of knee valgus.¹⁰ Because excessive knee valgus (MKD and 3D) is most likely caused by a combination of hip- and ankle-muscle imbalances, comprehensive strategies that focus on the joints proximal and distal to the knee should be investigated to determine if knee alignment can be corrected during functional tasks.Interventions have been developed to reduce the risk of lower extremity injury.^16–19 In a recent review²⁰ of intervention programs, the authors concluded that many focus on limiting valgus positioning during dynamic activity. In fact, participation in an injury prevention program may be most beneficial to individuals with poor movement quality.^21,22 Identifying and classifying individuals based on performance during functional tasks is common.^8,9,23–25 They are observed during squatting or jumping to identify poor movement quality, which is theorized to increase the risk of injury. For example, Myer et al²¹ classified female athletes into high-risk and low-risk categories based on external knee-abduction moment. After completing a training program, participants with greater levels of abduction moment, and thus theoretically higher risk, reduced abduction moment postintervention. DiStefano et al²² observed similar results when athletes were grouped using a clinical screening examination that incorporated 2D videography (Landing Error Scoring System). When compared with individuals who had better landing mechanics, those with poorer landing mechanics improved their scores in response to an exercise intervention. Identifying poor movement patterns allows clinicians to prescribe focused corrective exercise interventions to high-risk individuals.The DLS test is a common screening task used during functional movement examinations.^26,27 During the DLS test, a participant squats 5 times; if visual knee valgus is observed, then 2-in (5.08-cm) heel lifts are placed under both heels, and 5 additional squats are performed.^9,23 Squatting on a heel lift is theorized to differentiate between ankle and hip-muscle imbalance as the primary contributor to dynamic knee valgus.^9,23 As previously mentioned, if visual knee valgus is corrected when the squats are performed on the lift, then restrictions in ankle motion (restricted dorsiflexion) are thought to be the primary contributor to knee valgus.⁹ The heel lift results in ankle plantar flexion and alleviates the dorsiflexion restriction caused by the gastrocnemius and soleus, thereby normalizing knee alignment during the squat. Previous researchers^9,23 using this classification system have observed that participants with dynamic valgus that is corrected by a heel lift have tight and weak ankle plantar flexors compared with individuals with proper squat technique. However, to our knowledge, no investigators have determined if knee valgus can be altered in individuals who have been screened via this classification system.The primary purpose of our study was to determine if an exercise training program could decrease knee valgus during the DLS in individuals with visually identified knee valgus that was corrected with a heel lift. A secondary purpose was to determine if the training program could alter hip strength and ankle-dorsiflexion ROM, because these factors are believed to be related to knee-valgus alignment. Our general hypothesis was that knee valgus would be improved after a comprehensive training program focused on the joints proximal and distal to the knee as a result of improved hip strength and increased ankle ROM.     

Disinhibitory Interventions and Voluntary Quadriceps Activation: A Systematic Review

Objective:

To determine the effects of various therapeutic interventions on increasing voluntary quadriceps muscle activation.

Background:

Decreased voluntary quadriceps activation is commonly associated with knee injury. Recently, research has focused on developing specific disinhibitory interventions to improve voluntary quadriceps activation; yet, it remains unknown which interventions are most effective in promoting this improvement.

Data Sources:

We searched Web of Science from January 1, 1965 through September 27, 2012, using the key words quadriceps activation and transcutaneous electrical nerve stimulation, transcranial magnetic stimulation, cryotherapy, focal joint cooling, joint mobilization, joint mobilisation, joint manipulation, manual therapy, and neuromuscular electrical stimulation.

Study Selection:

Studies evaluating the effect of disinhibitory interventions on volitional quadriceps activation were used in our review. Standardized effect sizes (Cohen d) and 95% confidence intervals (CIs) were calculated from voluntary quadriceps activation means and standard deviations measured at baseline and at all available postintervention time points from each study.

Data Synthesis:

Ten studies were grouped into 5 categories based on intervention type: manual therapy (4 studies), transcutaneous electrical nerve stimulation (2 studies), cryotherapy (2 studies), neuromuscular electrical stimulation (2 studies), and transcranial magnetic stimulation (1 study). Transcutaneous electrical nerve stimulation demonstrated the strongest immediate effects (d = 1.03; 95% CI = 0.06, 1.92) and long-term effects (d = 1.93; 95% CI = 0.91, 2.83). Cryotherapy (d = 0.76; 95% CI = −0.13, 1.59) and transcranial magnetic stimulation (d = 0.54; 95% CI = −0.33, 1.37) had moderate immediate effects in improving voluntary quadriceps activation, whereas manual therapy (d = 0.38; 95% CI = −0.35, 1.09) elicited only weak immediate effects. Neuromuscular electrical stimulation produced weak negative to strong positive effects (range of d values = −0.50 to 1.87) over a period of 3 weeks to 6 months.

Conclusions:

Transcutaneous electrical nerve stimulation demonstrated the strongest and most consistent effects in increasing voluntary quadriceps activation and may be the best disinhibitory intervention for improving the same.Key Words: arthrogenic muscle inhibition, disinhibitory modalities, kneeQuadriceps function is critical for optimal locomotion and energy attenuation in the lower extremity.^1,2 The ability to eccentrically contract the quadriceps is critical for optimal knee range of motion during the weight-acceptance phase of gait.¹ It is hypothesized that patients with quadriceps dysfunction lack the ability to eccentrically contract the quadriceps in an effort to obtain optimal knee range of motion, which is critical for attenuating energy and maintaining proper contact forces at the joint surfaces.³ Physical performance, as demonstrated with the get-up-and-go test, is also impaired in patients with knee injuries,⁴ indicating that concentric quadriceps dysfunction may limit patients'' ability to propel themselves during ambulation. After knee injury, patients often display stiffer knee-movement strategies or less knee flexion during the stance phase of gait, which is thought to alter joint contact forces and increase the risk of joint deterioration.³Quadriceps dysfunction predicts a compound variable of both physical performance and self-reported function⁵ in patients with knee osteoarthritis as well as mortality⁶ in patients with chronic obstructive pulmonary disorder. Osteoarthritis,⁷ total knee arthroplasty,⁸ anterior knee pain,⁹ and anterior cruciate ligament deficiency or reconstruction¹⁰ are examples of knee injuries that present with quadriceps dysfunction, suggesting that proper functioning of this muscle group is critical for patients to maintain an acceptable quality of life with a broad range of conditions.Impaired functioning of this crucial muscle group is thought to arise from central nervous system alterations presenting as decreased motor output of the knee extensors.¹¹ These neural alterations after knee injury often manifest as decreased voluntary quadriceps activation,¹⁰ which can be modulated by altered excitability of spinal reflexive^12,13 and cortical¹⁴ motor pathways. Immediately after knee joint injury, a decrease in voluntary quadriceps activation may be a protective mechanism to prevent further injury.^15–17 However, if these neural abnormalities are not targeted with specific interventions used to disinhibit an inhibited muscle, quadriceps dysfunction may persist and become a factor limiting successful knee-injury management.¹¹Conventional rehabilitation strategies typically focus on strength training to reestablish normal quadriceps function without specifically addressing decreased voluntary quadriceps activation.¹¹ Traditional therapeutic exercise has demonstrated minimal improvements in quadriceps strength and voluntary quadriceps activation¹⁸ and small effects in decreasing pain (standardized mean difference = 0.40) and improving disability (standardized mean difference = 0.37).¹⁹ Because restoring voluntary quadriceps activation predicts the ability to develop quadriceps muscle strength in clinical populations, interventions targeting these activation deficits seem imperative.²⁰ A new rehabilitative paradigm has been proposed that seeks to combine interventions to increase voluntary quadriceps activation with traditional therapeutic exercise to improve clinical outcomes.^11,15,17 Techniques specifically used to alter motor excitability after joint injury for the purpose of improving voluntary quadriceps activation and to enhance therapeutic exercise are termed disinhibitory interventions.¹⁵ Disinhibitory interventions are intended to alter neuromuscular function by targeting mechanoreceptors locally at the injured joint, targeting the peripheral nervous system at points either proximal or distal to the injured joint, or targeting the central nervous system directly.To date, a systematic evaluation of viable interventions that can effectively disinhibit the quadriceps, thus increasing voluntary quadriceps activation, has not been performed. Therefore, the purpose of our study was to investigate the effectiveness of documented disinhibitory interventions for increasing voluntary quadriceps activation. It is imperative to understand the preliminary effects of a variety of disinhibitory interventions as a foundation for further research that will guide future rehabilitative science and improve knee-injury management.     

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.     

Fatigue-Induced Alterations of Static and Dynamic Postural Control in Athletes With a History of Ankle Sprain

Context:

Sensorimotor control is impaired after ankle injury and in fatigued conditions. However, little is known about fatigue-induced alterations of postural control in athletes who have experienced an ankle sprain in the past.

Objective:

To investigate the effect of fatiguing exercise on static and dynamic balance abilities in athletes who have successfully returned to preinjury levels of sport activity after an ankle sprain.

Design:

Cohort study.

Setting:

University sport science research laboratory.

Patients or Other Participants:

30 active athletes, 14 with a previous severe ankle sprain (return to sport activity 6–36 months before study entry; no residual symptoms or subjective instability) and 16 uninjured controls.

Intervention(s):

Fatiguing treadmill running in 2 experimental sessions to assess dependent measures.

Main Outcome Measure(s):

Center-of-pressure sway velocity in single-legged stance and time to stabilization (TTS) after a unilateral jump-landing task (session 1) and maximum reach distance in the Star Excursion Balance Test (SEBT) (session 2) were assessed before and immediately after a fatiguing treadmill exercise. A 2-factorial linear mixed model was specified for each of the main outcomes, and effect sizes (ESs) were calculated as Cohen d.

Results:

In the unfatigued condition, between-groups differences existed only for the anterior-posterior TTS (P = .05, ES = 0.39). Group-by-fatigue interactions were found for mean SEBT (P = .03, ES = 0.43) and anterior-posterior TTS (P = .02, ES = 0.48). Prefatigue versus postfatigue SEBT and TTS differences were greater in previously injured athletes, whereas static sway velocity increased similarly in both groups.

Conclusions:

Fatiguing running significantly affected static and dynamic postural control in participants with a history of ankle sprain. Fatigue-induced alterations of dynamic postural control were greater in athletes with a previous ankle sprain. Thus, even after successful return to competition, ongoing deficits in sensorimotor control may contribute to the enhanced ankle reinjury risk.Key Words: sensorimotor control, neuromuscular activity, copers, balance, time to stabilization, Star Excursion Balance Test

Key Points

• When athletes were tested in the unfatigued state, only minimal differences in postural control were detected between athletes who had fully recovered from an ankle sprain and uninjured controls.
• Injured participants experienced larger fatigue-induced alterations of dynamic postural control than healthy controls.
• Persistent sensorimotor control deficits in recovered athletes might remain undetected in the unfatigued state.

Ankle sprains are the most common game-related injuries in team ball-sport athletes,¹ and are often associated with decreases in sensorimotor control, including proprioception (reduced joint position sense and kinesthesia), muscular strength, and balance performance (static and dynamic postural control). These alterations have been reported in individuals after acute ankle sprain^2,3 and in those with chronic ankle instability (CAI).^2,3 Along with additional complaints, such as swelling, pain, or episodes of “giving way,” sensorimotor deficits persist even years after injury.^4,5 Consequently, sensorimotor impairments associated with lower extremity injuries may contribute to performance impairments⁶ and increase the reinjury risk.⁷ Athletes who successfully return to high-level sports activities and report normal function without persistent complaints have previously been defined as copers.⁸ However, recent studies suggest that even though functional performance and self-reported disability in ankle-sprain copers are similar to those in individuals who have never sustained an ankle sprain,⁸ sensorimotor control might still be affected.^9,10The incidence of match injuries in soccer players increases toward the end of both halves,¹¹ suggesting that physical fatigue might play an important role in injury-related sensorimotor control changes. This concept is supported by a number of studies examining sensorimotor alterations after fatiguing exercise in healthy, uninjured participants; among the observed changes were reduced muscle strength and activity,¹² and altered proprioception¹³ and kinematics.¹⁴ Additionally, static postural control was assessed in most of these studies, showing an increase in postural sway due to localized fatigue of the ankle,¹⁵ knee, and hip¹⁶ muscles that can persist up to 10 minutes after exercise ends.¹⁷ Comparable results have been shown for fatiguing multijoint exercises¹⁷ and whole-body fatigue.¹⁸ Authors of only 2 studies have investigated the effects of fatiguing exercises on dynamic measures of postural control in healthy individuals¹⁹ and participants with CAI²⁰; however, because of different study populations and testing modalities, the effects remain uncertain.The findings described above suggest that long-term impairment of sensorimotor control exists after an ankle sprain and may even be present in those who do not develop persistent functional impairments and successfully return to preinjury levels of sport activity. To our knowledge, only 1 study²⁰ specifically investigated the effect of exercise-induced fatigue on participants with a previous ankle injury. Based on the findings of Gribble et al,²⁰ we hypothesize that these impairments are small under regular conditions but could expose athletes to an increased injury risk when they physically fatigue during intensive exercise.Therefore, the aim of our study was to investigate fatigue-induced alterations of static and dynamic postural control in a sample of ankle sprain copers and to compare the effects with those of uninjured controls. We proposed that changes in postural control due to fatigue would be more substantial in previously injured participants than in controls.     

Instruction and Jump-Landing Kinematics in College-Aged Female Athletes Over Time

Context:

Instruction can be used to alter the biomechanical movement patterns associated with anterior cruciate ligament (ACL) injuries.

Objective:

To determine the effects of instruction through combination (self and expert) feedback or self-feedback on lower extremity kinematics during the box–drop-jump task, running–stop-jump task, and sidestep-cutting maneuver over time in college-aged female athletes.

Design:

Randomized controlled clinical trial.

Setting:

Laboratory.

Patients or Other Participants:

Forty-three physically active women (age = 21.47 ± 1.55 years, height = 1.65 ± 0.08 m, mass = 63.78 ± 12.00 kg) with no history of ACL or lower extremity injuries or surgery in the 2 months before the study were assigned randomly to 3 groups: self-feedback (SE), combination feedback (CB), or control (CT).

Intervention(s):

Participants performed a box–drop-jump task for the pretest and then received feedback about their landing mechanics. After the intervention, they performed an immediate posttest of the box–drop-jump task and a running–stop-jump transfer test. Participants returned 1 month later for a retention test of each task and a sidestep-cutting maneuver. Kinematic data were collected with an 8-camera system sampled at 500 Hz.

Main Outcome Measure(s):

The independent variables were feedback group (3), test time (3), and task (3). The dependent variables were knee- and hip-flexion, knee-valgus, and hip- abduction kinematics at initial contact and at peak knee flexion.

Results:

For the box–drop-jump task, knee- and hip-flexion angles at initial contact were greater at the posttest than at the retention test (P < .001). At peak knee flexion, hip flexion was greater at the posttest than at the pretest (P = .003) and was greater at the retention test than at the pretest (P = .04); knee valgus was greater at the retention test than at the pretest (P = .03) and posttest (P = .02). Peak knee flexion was greater for the CB than the SE group (P = .03) during the box–drop-jump task at posttest. For the running–stop-jump task at the posttest, the CB group had greater peak knee flexion than the SE and CT (P ≤ .05).

Conclusions:

Our results suggest that feedback involving a combination of self-feedback and expert video feedback with oral instruction effectively improved lower extremity kinematics during jump-landing tasks.Key Words: augmented feedback, technique instruction, box-drop jump, running-stop jump, sidestep-cutting maneuver

Key Points

• The use of oral and combo video feedback improved lower extremity biomechanics during jump-landing tasks.
• Combined self- and expert video feedback with oral instruction after a box–drop-landing task improved peak knee-flexion angles.
• Combining self- and expert video feedback is an easy, effective tool for changing lower extremity kinematics.
• The use of oral and video feedback for a box–drop-jump task did not transfer to improved lower extremity biomechanics during a sidestep-cutting maneuver.

An increasing number of anterior cruciate ligament (ACL) injuries have occurred in various sports, including basketball, soccer, and volleyball, over the past 15 years.^1–4 A noncontact mechanism accounts for approximately 72% of all ACL injuries and typically occurs during activities that include deceleration, jump landing, and sidestep cutting.^5–8 Anterior cruciate ligament injuries carry short-term consequences, such as surgical repair, extensive rehabilitation, and a loss of athletic identity, and serious long-term consequences, such as osteoarthritis and joint laxity.^9–11 A patient with a history of knee injury during adolescence has a 3 times greater risk of developing osteoarthritis by age 65 years than a patient without this history.¹⁰ Several potential risk factors have been identified as contributors to noncontact ACL injuries, including biomechanical risk factors such as muscular strength, body movement and forces, skill level, muscular activation, and neuromuscular control.^6,7Researchers^9,12–17 frequently have studied lower extremity kinematics during activities, such as landing or decelerating, that place the participant at risk for injury to find alignments that might put the body in an at-risk position. Decreased knee and hip flexion, increased knee valgus, increased hip internal rotation, and decreased hip abduction are common lower extremity alignments seen during noncontact ACL injuries and are considered to be at-risk body positions.^9,11,13 For example, decreased knee-flexion angles while landing cause the hamstrings to less effectively protect the ACL from the anterior tibial translation caused by the quadriceps exerting maximal anterior shear force at the small knee-flexion angle.^6,7,18–20 Therefore, programs designed to improve strength and balance and to instruct athletes in proper lower extremity alignment during jump-landing activities often are used to decrease the risk of ACL injury.^21–25These injury-prevention programs have succeeded in demonstrating that an athlete''s biomechanics can be altered. The focus of most prevention programs, whether they are based on plyometrics, balance, or instruction, is on improving landing or decelerating technique and incorporates oral and visual feedback.^26–33 These types of feedback are considered augmented feedback because they are from an external source that is provided to the learner.³⁴ Augmented feedback can be divided into 3 different categories: knowledge of results, knowledge of performance, and biofeedback.^34,35 Many injury-prevention programs frequently use knowledge of performance feedback, which includes information about the characteristics of a movement that lead to prescribed outcomes.³⁵Augmented feedback recently has been used to decrease the biomechanical risk factors associated with ACL injuries.^28,36–39 For example, oral and video feedback decrease ground reaction forces from a box–drop-landing, and the combination of self-feedback and expert video feedback (combo feedback) improves knee-flexion angles at peak knee flexion during a running–stop-jump task.^28,36,37 However, no one knows if using a simple clinical feedback tool will improve biomechanical risk factors associated with jump-landing activities over time and which form of feedback (self or combo) is most effective. In addition, no one knows if feedback on a simple jump-landing task will transfer to an improvement in more sport-specific tasks. Therefore, our primary purpose was to determine whether instruction (self or combo) would affect box-drop, running–stop-jump, and sidestep-cutting maneuver lower extremity kinematics (knee flexion, knee valgus, hip flexion, hip abduction) over time in healthy college-aged female athletes. We hypothesized that combo feedback would improve lower extremity kinematics (eg, increased knee flexion, decreased knee valgus, and increased hip abduction) better than self-feedback or no feedback. Our secondary purpose was to determine if feedback related to the box–drop-jump task would transfer to an improvement in running–stop-jump task and sidestep-cutting maneuver lower extremity kinematics. We hypothesized that combo feedback for the box–drop-jump technique would improve lower extremity kinematics for the running–stop-jump task and sidestep-cutting maneuver.     

Scapular Bracing and Alteration of Posture and Muscle Activity in Overhead Athletes With Poor Posture

Context

Overhead athletes commonly have poor posture. Commercial braces are used to improve posture and function, but few researchers have examined the effects of shoulder or scapular bracing on posture and scapular muscle activity.

Objective

To examine whether a scapular stabilization brace acutely alters posture and scapular muscle activity in healthy overhead athletes with forward-head, rounded-shoulder posture (FHRSP).

Design

Randomized controlled clinical trial.

Setting

Applied biomechanics laboratory.

Patients or Other Participants

Thirty-eight healthy overhead athletes with FHRSP.

Intervention(s)

Participants were assigned randomly to 2 groups: compression shirt with no strap tension (S) and compression shirt with the straps fully tensioned (S + T). Posture was measured using lateral-view photography with retroreflective markers. Electromyography (EMG) of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) in the dominant upper extremity was measured during 4 exercises (scapular punches, W''s, Y''s, T''s) and 2 glenohumeral motions (forward flexion, shoulder extension). Posture and exercise EMG measurements were taken with and without the brace applied.

Main Outcome Measure(s)

Head and shoulder angles were measured from lateral-view digital photographs. Normalized surface EMG was used to assess mean muscle activation of the UT, MT, LT, and SA.

Results

Application of the brace decreased forward shoulder angle in the S + T condition. Brace application also caused a small increase in LT EMG during forward flexion and Y''s and a small decrease in UT and MT EMG during shoulder extension. Brace application in the S + T group decreased UT EMG during W''s, whereas UT EMG increased during W''s in the S group.

Conclusions

Application of the scapular brace improved shoulder posture and scapular muscle activity, but EMG changes were highly variable. Use of a scapular brace might improve shoulder posture and muscle activity in overhead athletes with poor posture.Key Words: shoulder, upper extremity, electromyography, braces

Key Points

• • Changes occurred in forward shoulder angle and the electromyographic activity of the upper, middle, and lower trapezius muscles when participants wore the scapular-stabilizing brace.
• • The compression garment and the tension straps selectively affected posture by reducing forward shoulder angle, but associated electromyographic activity changes were small and do not appear to be influenced by strap tension.
• • Scapular bracing appeared to produce beneficial changes in muscular activity and posture in healthy overhead athletes.
• • Clinicians might consider using a scapular brace as an adjunct to prerehabilitation and rehabilitation exercises in the athlete with poor posture.

Shoulder injuries are a common and disabling condition among athletes, particularly overhead athletes (baseball, softball, swimming, volleyball, track and field throwing events, and tennis). Recent National Collegiate Athletic Association (NCAA) injury-surveillance system research has shown that shoulder injuries account for 39.4% of all injuries in baseball,¹ 15.8% of injuries in softball,² and 21.7% of injuries in volleyball.³ Most of these injuries are classified as overuse injuries of muscles, tendons, and other tissues within the joint.^4–7 These overuse injuries can result from incorrect posture, mechanics, or techniques during overhead throwing, hitting, or striking motions.^8–10 Therefore, when working with athletes involved in overhead sports, clinicians should address posture, as well as sport-specific mechanics, during the evaluation and rehabilitation process.Forward-head, rounded-shoulder posture (FHRSP) is a specific postural anomaly that might play a role in the development of shoulder pain and pathologic conditions. Both forward-head (FH) and rounded-shoulder (RS) postures are defined as excessive anterior orientation of the head or glenohumeral joint relative to the vertical plumb line of the body.^8,11 These postural abnormalities often occur in conjunction and might be associated with other overuse injuries in the shoulder.^11–14 Many clinicians and researchers^8,14–16 believe that FHRSP alters scapular mechanics and muscular activity about the shoulder complex, causing altered force couples and scapular motions that result in tissue overuse, injury, and pain. Greenfield et al¹³ reported greater FH posture in patients with shoulder conditions than in healthy control participants. Griegel-Morris et al¹⁷ found an association between both FH and RS postures and reports of shoulder or scapular pain. Patients with preexisting FHRSP exhibited greater anterior tilt and upward rotation of the scapula during flexion motions at the shoulder.¹⁶ Acutely, adopting a FHRSP also creates increased scapular anterior tilt and upward rotation.¹⁸ Both of these specific scapular positions are related to shoulder conditions, suggesting that head and shoulder posture might influence the development and progression of overuse injuries.^8,14,15The altered positions of the scapula seen in individuals displaying FHRSP might change the electromyographic (EMG) activity of the musculature surrounding the scapula and glenohumeral joint, leading to tissue overload and injury. Patients with overuse shoulder conditions commonly display decreased serratus anterior (SA) and lower trapezius (LT) activity during shoulder motions.^8,16,19–21 Most researchers^8,14,15 believe that these altered EMG patterns disrupt the normal force couples surrounding the scapula, leading to dyskinesis and increasing the risk of pain. Researchers^16,19,20 studying participants with FH, RS, or both, postures have demonstrated that these postures are related to decreased SA activity and increased upper trapezius (UT) activity. Given that these alterations in SA and UT activity have been observed in individuals with shoulder conditions, posture might play an important role in the development or progression of overuse shoulder injuries.²¹One method for restoring normal posture and muscular activity around the scapula involves bracing or taping the scapulothoracic articulation. Scapular taping typically involves having the patient retract and depress the scapula, then applying tape over the scapular spine and medial border.^11,22–25 The patients who have used scapular taping generally displayed altered scapular position, decreased UT muscle activity, and decreased or improved pain profiles.^11,23–25 However, the application of adhesive tape might cause skin irritation in some patients and might not be a feasible intervention for daily or prolonged use. Based on the results of this research, companies have developed braces that patients can use to improve scapular position and muscle activity and treat shoulder conditions. These braces are designed to alter the posture of the shoulder and thoracic spine, causing favorable changes in scapular position, muscle activity, and movement . In studies of 15 healthy participants and 15 participants with scapular dyskinesis, Uhl et al^26,27 found that wearing 1 type of commercially available scapular brace increased posterior tipping, decreased upward rotation in the dominant and nondominant upper extremities, and decreased internal rotation during the lowering phase of elevation. They concluded^26,27 that the brace affected scapular position at rest and in the lower ranges of motion and might assist the scapular muscles in controlling scapular motion. Walther et al²⁸ compared the effects of a functional brace with traditional rehabilitation and home-based programs in a group of participants with subacromial impingement syndrome. After 6 and 12 weeks, the braced group demonstrated the same improvements in shoulder pain and function as traditional rehabilitation groups. The authors²⁸ concluded that bracing might be as effective as traditional methods for treating impingement syndrome. Thus, bracing might be a new tool to help correct scapular position and treat pain in individuals with shoulder conditions.Scapular braces commonly are used for athletes with shoulder conditions in conjunction with rehabilitation. Clinically, athletic trainers might use bracing or taping to complement a corrective exercise program or might use bracing or taping to restore more normal length-tension relationships in muscles during the exercise program itself. Because of this, a better understanding of the effects these braces have on healthy individuals is needed. In the few studies of the effects of bracing or taping on the shoulder girdle, investigators have not examined short-term changes that take place during the performance of rehabilitative exercises, and no researchers have evaluated the effects of a brace application on factors such as scapular muscle activity and posture in healthy overhead athletes. Therefore, the purpose of our study was to examine whether a scapular stabilization brace acutely altered posture and scapular muscle activity in healthy overhead athletes with FHRSP while performing 4 common rehabilitation exercises and 2 functional shoulder movements compared with not wearing the brace.     

Different Modes of Feedback and Peak Vertical Ground Reaction Force During Jump Landing: A Systematic Review

Context:

Excessive ground reaction force when landing from a jump may result in lower extremity injuries. It is important to better understand how feedback can influence ground reaction force (GRF) and potentially reduce injury risk.

Objective:

To determine the effect of expert-provided (EP), self-analysis (SA), and combination EP and SA (combo) feedback on reducing peak vertical GRF during a jump-landing task.

Data Sources:

We searched the Web of Science database on July 1, 2011; using the search terms ground reaction force, landing biomechanics, and feedback elicited 731 initial hits.

Study Selection:

Of the 731 initial hits, our final analysis included 7 studies that incorporated 32 separate data comparisons.

Data Extraction:

Standardized effect sizes and 95% confidence intervals (CIs) were calculated between pretest and posttest scores for each feedback condition.

Data Synthesis:

We found a homogeneous beneficial effect for combo feedback, indicating a reduction in GRF with no CIs crossing zero. We also found a homogeneous beneficial effect for EP feedback, but the CIs from 4 of the 10 data comparisons crossed zero. The SA feedback showed strong, definitive effects when the intervention included a videotape SA, with no CIs crossing zero.

Conclusions:

Of the 7 studies reviewed, combo feedback seemed to produce the greatest decrease in peak vertical GRF during a jump-landing task.Key Words: injury prevention, knee, feedback, landing biomechanics

Key Points

• All modes of feedback effectively reduced ground reaction force during a jump-landing task.
• Combination feedback demonstrated the strongest effect sizes for reducing ground reaction force compared with expert-provided and self-analysis feedback.
• More high-quality studies are needed to support the use of feedback interventions for altering lower extremity landing forces and decreasing lower extremity injury risk.

Landing is an essential athletic task used during many different sporting activities, including basketball, volleyball, and gymnastics.^1–3 The act of jumping and landing during these different sporting activities involves different magnitudes of ground reaction forces (GRFs).⁴ The GRF magnitudes have been reported to be greatest during the landing phase of a jump when the knee is between 0° and 25° of flexion, a point at which the knee must resist a rapid change in kinetic energy.⁵ Excessive GRFs may result in lower extremity injuries.^3,6–8The knee is largely responsible for energy attenuation of the lower extremity when landing from a jump,^9,10 so this joint may have increased susceptibility to injury during such a task. Researchers have identified the presence of damage to the subchondral bone, cartilage, and soft tissue due to extreme forces imposed on the lower extremity during selected landing activities.¹¹ A positive moderate correlation between increased vertical GRF and increased anterior tibial acceleration when landing from a jump supports the hypothesis that individuals landing with greater impact loads could have an increased risk of anterior cruciate ligament (ACL) injury.¹² Given that the main function of the ACL is preventing anterior translation of the tibia, landing with increased GRF and thus increased anterior tibial acceleration may place more strain on the ligament, increasing the likelihood of ligament rupture.To reduce the risk of injury associated with increased GRF during landing, different interventions have been used to decrease GRF by altering lower extremity biomechanics during landing. To our knowledge, no researchers have evaluated whether reducing an individual''s GRF decreases his or her risk of injury, but compelling data have suggested that higher GRF and other factors may increase the risk of substantially injuring the knee.¹³ Specifically, prospective data have shown that GRF during a jump-landing task was 20% higher in female athletes who sustained an ACL rupture than in athletes who did not.¹³ These data spark a compelling but unsubstantiated theory that reducing high GRFs may coincide with a decreased risk of knee injury. Clinical trials to evaluate the true prophylactic capabilities of reducing GRF to limit knee injuries are likely expensive and logistically difficult to conduct. Therefore, successfully identifying an intervention that can manipulate GRF is important before these studies are performed.Various methods have been implemented to teach proper landing biomechanics to prevent future injury.¹⁴ For example, feedback is a modality used to prompt an individual to correct potentially harmful biomechanics and reduce high GRF. Feedback can be defined as sensory information made available to the participant during or after a task in an attempt to alter a movement.¹⁵ It can include information related to the sensations associated with the movement (eg, the feel or sound the participant experiences while performing the task) or related to the result of the action with respect to the environmental goal.¹⁵ Different modes of feedback have been reported and include (1) expert-provided (EP) feedback through oral correction,¹⁶ oral instruction,^17,18 or visual demonstration¹⁶; (2) self-analysis (SA) feedback conducted with videotape correction^19,20 or self-correction from previous trials¹⁷; and (3) combination (combo) feedback that uses both EP and SA feedback.^19,21 Through EP feedback, professionals can analyze movements and provide various forms of oral and visual feedback to alter that task, whereas SA feedback requires the participant to identify movement characteristics that need to be altered and to adjust to change that specific task.Recently, a surge of injury-prevention programs have been implemented to reduce the risk of ACL injury in athletes.^22,23 These programs often incorporate feedback techniques and aim to reduce the risk of injury by teaching athletes to land properly to reduce stress on the lower extremity and potentially prevent acute and chronic lower extremity injuries.¹⁹ Altering the landing phase of a jump via various feedback methods could result in decreased GRFs and increased flexion angles at the knee, which may decrease the risk of lower extremity injury.Although programs incorporating feedback are increasing in popularity, the magnitude of the effect that different types of feedback have on reducing GRF has not been evaluated systematically. Knowledge of the efficacy of feedback on reducing potentially harmful GRF may help clinicians determine whether feedback should be incorporated into jump-landing training programs. Therefore, the purpose of our study was to systematically evaluate the current literature to determine the magnitude of immediate and delayed effects of EP, SA, and combo feedback interventions on reducing peak vertical GRF during a jump-landing task in healthy individuals.     

Sport-Related Concussion and Sensory Function in Young Adults

Context:

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

Objective:

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

Design:

Cross-sectional study.

Setting:

Research laboratory.

Patients or Other Participants:

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

Main Outcome Measure(s):

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

Conclusions:

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

Key Points

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

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

Clinical Examination Results in Individuals With Functional Ankle Instability and Ankle-Sprain Copers

Context:

Why some individuals with ankle sprains develop functional ankle instability and others do not (ie, copers) is unknown. Current understanding of the clinical profile of copers is limited.

Objective:

To contrast individuals with functional ankle instability (FAI), copers, and uninjured individuals on both self-reported variables and clinical examination findings.

Design:

Cross-sectional study.

Setting:

Sports medicine research laboratory.

Patients or Other Participants:

Participants consisted of 23 individuals with a history of 1 or more ankle sprains and at least 2 episodes of giving way in the past year (FAI: Cumberland Ankle Instability Tool [CAIT] score = 20.52 ± 2.94, episodes of giving way = 5.8 ± 8.4 per month), 23 individuals with a history of a single ankle sprain and no subsequent episodes of instability (copers: CAIT score = 27.74 ± 1.69), and 23 individuals with no history of ankle sprain and no instability (uninjured: CAIT score = 28.78 ± 1.78).

Intervention(s):

Self-reported disability was recorded using the CAIT and Foot and Ankle Ability Measure for Activities of Daily Living and for Sports. On clinical examination, ligamentous laxity and tenderness, range of motion (ROM), and pain at end ROM were recorded.

Main Outcome Measure(s):

Questionnaire scores for the CAIT, Foot and Ankle Ability Measure for Activities of Daily Living and for Sports, ankle inversion and anterior drawer laxity scores, pain with palpation of the lateral ligaments, ankle ROM, and pain at end ROM.

Results:

Individuals with FAI had greater self-reported disability for all measures (P < .05). On clinical examination, individuals with FAI were more likely to have greater talar tilt laxity, pain with inversion, and limited sagittal-plane ROM than copers (P < .05).

Conclusions:

Differences in both self-reported disability and clinical examination variables distinguished individuals with FAI from copers at least 1 year after injury. Whether the deficits could be detected immediately postinjury to prospectively identify potential copers is unknown.Key Words: laxity, chronic ankle instability, giving way, range of motion

Key Points

• Compared with copers, participants with functional ankle instability had greater self-reported disability, talar tilt laxity, and pain with inversion and limited sagittal-plane range of motion.
• Identifying dynamic coping mechanisms may help to improve ankle-sprain prevention and treatment strategies.

Functional ankle instability (FAI) is a common sequela of ankle sprain, affecting approximately 32% to 47% of patients with symptoms including sensations of giving way, subsequent sprains, and instability.^1–3 Because these symptoms can limit physical activity and activities of daily living for years after injury^2,3 and decrease quality of life,¹ significant resources have been dedicated to elucidating the mechanisms behind this condition. However, despite extensive research in this area, the factors that contribute to the development and continuation of FAI are still not clear.^4–6In the search to clarify current understanding, recent reports^7,8 have focused on ankle instability definitions and patient inclusion criteria. Delahunt et al⁷ highlighted the varied inclusion criteria in studies of chronic ankle instability and FAI. They emphasized that variability in the pathologic group may partially account for inconsistent findings in the research literature. In contrast to the highly variable FAI groups, the comparison groups in studies of ankle instability are very consistent. Comparison groups are generally individuals who have never sprained either ankle (the uninjured or control group).⁹ Some authors^10,11 have studied copers as an alternative comparison group: individuals with a history of lateral ankle sprain but no recurrent instability for at least 1 year postinjury. Rather than compare individuals with FAI with individuals who have never sprained an ankle, it may be more appropriate to compare them with individuals who have been exposed to the initial risk factor (lateral ankle sprain) but have not gone on to develop FAI.¹⁰ Although the precise mechanism of coping is still unknown,^11–14 insight into coping mechanisms may help explain why individuals with FAI are unable to cope after ankle sprain. Additionally, once identified, successful coping mechanisms may be useful in treating FAI.In recent years, a number of authors have included comparison groups of ankle-sprain copers.^11–14 Differences in functional performance,¹¹ self-assessed disability,^11–14 ligamentous laxity,¹² injury history,^11–13 lower extremity kinematics,¹⁴ ankle-joint stiffness,¹³ fibular position,¹³ and postural control^13,15 have been investigated. However, more information about the clinical profiles of these individuals is needed because it may help us to prospectively differentiate potential copers and noncopers (postsprain but before development of FAI). Clinicians could then target individuals who are likely to have recurrent injury, leading to more efficient use of resources and enhanced injury-prevention efforts. Such a prospective clinical screening evaluation already exists for patients with anterior cruciate ligament injuries.¹⁶ However, the ankle-instability literature is still several steps away from this type of measure.We believe one of the next steps to better understand ankle-sprain copers is to compile a profile of a typical coper, consisting of injury history, self-reported disability, and clinical examination and to compare that profile with the profiles of both individuals with FAI and uninjured individuals. Thus, the primary purpose of our study was to explore potential group (FAI, coper, and uninjured) differences in both self-reported variables (injury history and disability) and clinical examination variables (laxity, pain, and range of motion).     

Jump-Landing Biomechanics and Knee-Laxity Change Across the Menstrual Cycle in Women With Anterior Cruciate Ligament Reconstruction

Context:

Of the individuals able to return to sport participation after an anterior cruciate ligament(ACL) injury, up to 25% will experience a second ACL injury. This population may be more sensitive to hormonal fluctuations, which may explain this high rate of second injury.

Objective:

To examine changes in 3-dimensional hip and knee kinematics and kinetics during a jump landing and to examine knee laxity across the menstrual cycle in women with histories of unilateral noncontact ACL injury.

Design

 Controlled laboratory study.

Setting:

Laboratory.

Patients or Other Participants:

A total of 20 women (age = 19.6 ± 1.3 years, height = 168.6 ± 5.3 cm, mass = 66.2 ± 9.1 kg) with unilateral, noncontact ACL injuries.

Intervention(s)

Participants completed a jump-landing task and knee-laxity assessment 3 to 5 days after the onset of menses and within 3 days of a positive ovulation test.

Main Outcome Measure(s):

Kinematics in the uninjured limb at initial contact with the ground during a jump landing, peak kinematics and kinetics during the loading phase of landing, anterior knee laxity via the KT-1000, peak vertical ground reaction force, and blood hormone concentrations (estradiol-β-17, progesterone, free testosterone).

Results:

At ovulation, estradiol-β-17 (t = −2.9, P = .009), progesterone (t = −3.4, P = .003), and anterior knee laxity (t = −2.3, P = .03) increased, and participants presented with greater knee-valgus moment (Z = −2.6, P = .01) and femoral internal rotation (t = −2.1, P = .047). However, during the menses test session, participants landed harder (greater peak vertical ground reaction force; t = 2.2, P = .04), with the tibia internally rotated at initial contact (t = 2.8, P = .01) and greater hip internal-rotation moment (Z = −2.4, P = .02). No other changes were observed across the menstrual cycle.

Conclusions

Knee and hip mechanics in both phases of the menstrual cycle represented a greater potential risk of ACL loading. Observed changes in landing mechanics may explain why the risk of second ACL injury is elevated in this population.Key Words: hormones, estrogen, vertical ground reaction force, knee-valgus moment

Key Points

• Clinicians should be aware of the high rate of second injury and biomechanical consequences of many factors related to return to sport participation after anterior cruciate ligament (ACL) injury, including sensitivity to hormonal fluctuations and asymmetrical limb loading.
• The biomechanical profiles of women with ACL injury changed during the preovulatory phase of the menstrual cycle, possibly increasing the risk of second ACL injury.
• Women with ACL reconstructions should have their landing mechanics evaluated before returning to sport participation.
• Anterior knee laxity and jump-landing biomechanics changed across the menstrual cycle in women with unilateral ACL injuries.
• Both menstrual cycle phases had biomechanical variables associated with ACL loading.

The risk of sustaining a noncontact anterior cruciate ligament (ACL) injury is not equal across the menstrual cycle.^1–4 The menstrual cycle consists of the follicular, ovulatory, and luteal phases, which have markedly different hormonal profiles. The follicular phase is associated with the lowest concentrations of estrogen, progesterone, and testosterone. Ovulation, which follows the follicular phase, occurs between days 9 and 20 and is associated with a spike in luteinizing hormone and then a spike in estrogen.⁵ This is the largest concentration of estrogen during the menstrual cycle. The final phase of the menstrual cycle is the luteal phase, which is associated with prolonged elevated estrogen levels. Progesterone also increases substantially during this phase. Researchers^6,7 have reached consensus that the preovulatory phase (from the follicular phase to ovulation) of the menstrual cycle presents the highest risk for noncontact ACL injuries. The risk of injury is thought to result from hormonal fluctuations influencing tissue that, in turn, affects neuromuscular characteristics during dynamic tasks, such as landing from a jump.^8,9 Differences across menstrual cycle phases have been identified in variables believed to be associated with joint stability, including laxity,^5,10,11 muscle stiffness,⁹ strength,^12–14 proprioception,¹⁵ and muscle-activation patterns.¹⁶ However, this area is not without controversy, with other researchers^17–20 observing no change across the menstrual cycle in similar variables.Reproductive hormones seem to influence ACL laxity in females with normal menstrual cycles and physiologic levels of estrogen and progesterone.^5,11,21–25 Numerous authors have concluded that anterior laxity differs between sexes, with males having less laxity than females.^25–31 Again, this area is not without controversy, as several authors have concluded that anterior knee laxity does not change across the menstrual cycle.^18,31–36 However, negative correlations have been observed between ACL stiffness and estrogen concentration in active females, indicating that an increase in estrogen is associated with lower levels of ligament stiffness.²¹ Additionally, evidence^8,37,38 has suggested that ACL laxity may influence muscular response during dynamic activity. Park et al⁸ collected biomechanical data on 26 participants and initially observed no change in kinematic and kinetic variables across the 3 phases of the menstrual cycle. However, when they reorganized participants based on their relative levels of knee laxity into low-, medium-, and high-laxity time points, the authors found that the high-laxity group had a 30% increase in adduction impulse, 20% increase in adduction moment, and 45% increase in external rotation compared with the medium- and low-laxity groups.⁸ This information demonstrates that knee laxity can influence joint loading and potentially influence noncontact ACL injury.Besides knee laxity, other biomechanical factors are associated with ACL loading and ACL injury during jumping and landing. Landing with decreased sagittal-plane motion or moment (knee and hip extension) and increased frontal- and rotational-plane motion of the hip (adduction and internal rotation) and knee (valgus and internal rotation) contribute to ACL loading.³⁹ Researchers^8,40,41 have examined changes in jump-landing mechanics across the menstrual cycle in healthy female populations without histories of ACL injury. These authors observed no change in jump-landing hip and knee mechanics across the menstrual cycle, leading them to conclude that injury rates were most likely due to other factors, including strength or ligament properties.⁴¹ One limitation of these studies is that some women may be more responsive to hormonal fluctuations than others (ie, responders versus nonresponders).^5,11 We theorize that females with histories of ACL injury may be responsive to hormonal fluctuations, and this increased sensitivity may have a greater effect on tissue and ultimately landing mechanics. Additionally, up to 25% of individuals who sustain primary ACL ruptures will have second ACL injuries, with many second injuries occurring in the contralateral limb.^42–44 In a recent paper on second ACL injuries, Paterno et al⁴² examined athletes who were returning to high-level sports and observed that 75% of second ACL injuries occurred in the contralateral limb and 88% of individuals sustaining these injuries were females. The rate of second injury is particularly high for individuals returning to sport participation even after successfully completing rehabilitation programs.⁴⁴ This warrants further investigation because underlying risk factors, such as hormones, could play a role in the rates of second injury in the contralateral limb. Therefore, the purpose of our study was to examine anterior knee laxity and 3-dimensional hip and knee kinematics and kinetics across the menstrual cycle in a population of women with previous unilateral, noncontact ACL injuries. We hypothesized that biomechanical variables assessed during a jump landing would be altered at ovulation in ways that would increase ACL loading and laxity compared with menses. We based this theory on research in which investigators^5,38 have identified increased ligamentous laxity at ovulation. Additionally, we hypothesized that hip and knee kinematics and kinetics during a jump landing would change in ways associated with increased ACL loading.^5,38     

Altered Knee and Ankle Kinematics During Squatting in Those With Limited Weight-Bearing–Lunge Ankle-Dorsiflexion Range of Motion

Context:

Ankle-dorsiflexion (DF) range of motion (ROM) may influence movement variables that are known to affect anterior cruciate ligament loading, such as knee valgus and knee flexion. To our knowledge, researchers have not studied individuals with limited or normal ankle DF-ROM to investigate the relationship between those factors and the lower extremity movement patterns associated with anterior cruciate ligament injury.

Objective:

To determine, using 2 different measurement techniques, whether knee- and ankle-joint kinematics differ between participants with limited and normal ankle DF-ROM.

Design:

Cross-sectional study.

Setting:

Sports medicine research laboratory.

Patients or Other Participants:

Forty physically active adults (20 with limited ankle DF-ROM, 20 with normal ankle DF-ROM).

Main Outcome Measure(s):

Ankle DF-ROM was assessed using 2 techniques: (1) nonweight-bearing ankle DF-ROM with the knee straight, and (2) weight-bearing lunge (WBL). Knee flexion, knee valgus-varus, knee internal-external rotation, and ankle DF displacements were assessed during the overhead-squat, single-legged squat, and jump-landing tasks. Separate 1-way analyses of variance were performed to determine whether differences in knee- and ankle-joint kinematics existed between the normal and limited groups for each assessment.

Results:

We observed no differences between the normal and limited groups when classifying groups based on nonweight-bearing passive-ankle DF-ROM. However, individuals with greater ankle DF-ROM during the WBL displayed greater knee-flexion and ankle-DF displacement and peak knee flexion during the overhead-squat and single-legged squat tasks. In addition, those individuals also demonstrated greater knee-varus displacement during the single-legged squat.

Conclusions:

Greater ankle DF-ROM assessed during the WBL was associated with greater knee-flexion and ankle-DF displacement during both squatting tasks as well as greater knee-varus displacement during the single-legged squat. Assessment of ankle DF-ROM using the WBL provided important insight into compensatory movement patterns during squatting, whereas nonweight-bearing passive ankle DF-ROM did not. Improving ankle DF-ROM during the WBL may be an important intervention for altering high-risk movement patterns commonly associated with noncontact anterior cruciate ligament injury.Key Words: knee flexion, knee valgus, knee varus, anterior cruciate ligament, squat, jump landing

Key Points

• Nonweight-bearing ankle-dorsiflexion range of motion was not associated with changes in ankle or knee kinematics during the overhead-squat, single-legged squat, or jump-landing task.
• Greater ankle-dorsiflexion range of motion during the weight-bearing lunge resulted in greater sagittal-plane motion at the knee and ankle during the squatting tasks but not the jump landing.
• Compared with nonweight-bearing passive measures, ankle-dorsiflexion range of motion during the weight-bearing lunge may be a more sensitive measure for identifying those with high-risk movement patterns.

An estimated 350 000 anterior cruciate ligament (ACL) reconstructions are performed annually in the United States,¹ with most of those injuries occurring during sport participation by individuals between 15 and 25 years old.^2,3 Recent estimates have illustrated a national increase in ACL injuries of 67.8% during a 10-year period.⁴ In addition to those concerning numbers, 70% of ACL injuries result from noncontact mechanisms, defined as no contact with another player or piece of equipment, such as plant-and-cut maneuvers, landing from a jump, and decelerating.^5,6 The high incidence of noncontact ACL injury is driving researchers to investigate possible biomechanical and neuromuscular factors that may contribute to ACL injury.Dynamic maneuvers, such as the overhead-squat (OHS),⁷ single-legged squat (SLS),⁸ and jump-landing (JL)⁹ tasks, have been used in laboratory and clinical settings to elucidate faulty lower extremity movement patterns and to identify individuals potentially at risk for ACL injury. Some of the key patterns of movement identified are side-to-side (frontal-plane) or rotational (transverse-plane) movements at the knee because those movements place the greatest load on the ACL in combination with an anterior tibial shear force (sagittal plane).¹⁰ Anterior cruciate ligament loading is exacerbated when the knee is in a minimally flexed or hyperextended position in conjunction with a large quadriceps muscle contraction.^11,12 Noncontact ACL injury mechanisms are often described as landing in a relatively extended knee position (sagittal plane) combined with frontal- and transverse-plane loading.¹² Movement at adjacent joints also influences knee loading. Researchers^7,13,14 have identified a potential relationship between limited dorsiflexion range of motion (DF-ROM) in the ankle and knee kinematics, such as medial knee displacement, which may increase the risk of ACL injury. Ideally, those squatting and JL movements would include primarily sagittal-plane motion at all lower extremity joints to perform properly and absorb and dissipate the landing forces.¹⁵ Restrictions in the ability to move through ankle DF during weight bearing can interfere with performance by potentially increasing the plantar-flexion moment when the ankle is dorsiflexed¹⁶ and restricting the forward rotation of the shank at the ankle when the foot is in contact with the ground.¹⁷ Limitations in ankle-DF displacement are often accompanied by less sagittal-plane motion at proximal joints, such as the knee and trunk.^15,18 Therefore, ankle-DF restrictions may contribute to limited sagittal-plane motion at the knee and thereby contribute to compensatory increases in frontal- and transverse-plane motions that are potentially injurious to the ACL.Less DF-ROM assessed passively in a nonweight-bearing (NWB) position has been associated with greater medial-knee displacement during a variety of tasks.^7,14 Bell et al⁷ studied individuals with medial-knee displacement, which is a clinical observation of dynamic valgus collapse, and observed that participants who displayed medial-knee displacement during an OHS had approximately 20% less NWB, passive ankle DF than did those participants without medial-knee displacement. Furthermore, the medial-knee displacement observed during the OHS was corrected when a 2-in (5.08-cm) lift was placed under the heel; the correction may have occurred because of the increased tibial angle in the anterior direction. Less passive DF-ROM assessed in NWB movements has also been associated with greater frontal-plane knee excursion during a double-legged drop-landing in young female soccer players¹⁴ and with decreased knee-flexion displacement during a jump-landing task.¹⁹Other authors have investigated ankle-DF motion during dynamic movements in relation to knee kinematics, with contrasting findings. Compared with men, women with greater DF-ROM measured during SLS²⁰ and double-legged drop landings²¹ demonstrated greater maximum knee-valgus angles. This body of research suggests that ankle DF-ROM may contribute to the amount of knee valgus (frontal plane) and knee flexion (sagittal plane) an individual uses during dynamic movement, but the relationship is unclear and requires further investigation.Previous examinations^7,14,19 of the relationship between ankle DF-ROM and knee kinematics may be limited because of the NWB, passive assessments that were often used. Weight-bearing measures of ankle DF-ROM may provide a better representation of the available ROM during functional, weight-bearing tasks.²² However, previous authors have not, to our knowledge, investigated the relationship between knee kinematics during dynamic movement and separate weight-bearing and NWB ankle DF-ROM assessments. In addition, no previous researchers, to our knowledge, have intentionally recruited a participant population with known limitations in ankle DF-ROM. Therefore, the purpose of our study was to investigate knee and ankle kinematics during dynamic tasks in participants who were identified as having limited ankle DF-ROM and to compare the results with those of participants who had normal ankle DF-ROM. Ankle-DF motion was assessed passively through both weight-bearing and NWB techniques before testing, and total displacement during dynamic movement was calculated. The goal of comparing the ROM of normal and limited groups was to find an assessment that could be used clinically to indicate how an individual will perform during a more functional task. We hypothesized that individuals with less DF-ROM, both NWB and weight bearing, would display kinematics associated with ACL loading (less sagittal-plane motion and greater frontal-plane motion) during an OHS, SLS, and JL task.     

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.