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.     

Sex Differences in Dynamic Closed Kinetic Chain Upper Quarter Function in Collegiate Swimmers

Context:

Upper quarter injuries have a higher incidence in female swimmers; however, to date, there are few ways to assess the basic functional ability of this region. The upper quarter Y balance test (YBT-UQ) may assist in this process because it was developed to provide a fundamental assessment of dynamic upper quarter ability at the limit of stability.

Objective:

To examine how sex affects performance on the YBT-UQ in swimmers.

Design:

Cohort study.

Patients or Other Participants:

Forty-three male and 54 female National Collegiate Athletic Association Division I college swimmers were recruited preseason.

Main Outcome Measure(s):

We measured YBT-UQ performance for the left and right limbs in the medial, inferolateral, and superolateral directions. The maximum score for each direction was normalized to upper extremity length. The average of the greatest normalized reach scores in each reach direction was used to develop a composite score (average distance in 3 directions/limb length [LL] × 100). To examine reach symmetry between sexes, the difference in centimeters between the left and right sides was calculated for each reach direction prior to normalization. Statistical analysis was conducted using an independent-samples t test (P < .05).

Results:

Average scores in the medial (women: 92.5 ± 7.4%LL, men: 100.0 ± 8.7%LL; P < .01) and inferolateral (women: 85.6 ± 10.3%LL, men: 89.8 ± 10.8%LL; P = .05) directions and composite score (women: 83.4 ± 8.3%LL, men: 88.3 ± 8.9%LL; P < .01) were higher in men than in women. No differences were observed for reach symmetry in any direction.

Conclusions:

Performance on several YBT-UQ indices was worse for female than male collegiate swimmers. These results may have implications for the use of preseason and return-to-sport testing in swimmers as a measurement of upper quarter function and symmetry.Key Words: Y-Balance test, core stability, shoulder function, injury risk

Key Points

• Female collegiate swimmers exhibited worse performance than their male counterparts on the upper quarter Y- balance test in the medial and inferolateral directions as well as in the average overall score.
• No sex differences existed for reach symmetry for any of the reach directions.
• The worse performance in women may be associated with shoulder and core stability limitations, which may explain the increased incidence of upper quarter injuries in female swimmers.

Upper quarter injuries are the most common injuries sustained by collegiate swimmers.^1,2 More specifically, female swimmers have an increased risk of upper quarter injuries of the shoulder and back/neck compared with their male counterparts.^1,2 Sallis et al³ found that female swimmers sustained 21.05 and 8.19 injuries/100 participant years, whereas male swimmers experienced 6.55 and 1.45 injuries/100 participant years for the shoulder and back/neck, respectively. These injuries are disabling, often contribute to decreased performance and missed practices and competitions, and may require surgery. A number of extrinsic and intrinsic variables have been shown to contribute to the increased risk of upper quarter injuries, regardless of sex.^2,4–11 Extrinsic factors include rigorous training exposure focusing on shoulder-intensive movements, reduced cross-training or participation in other sports, prior injury, and age. Intrinsic risk factors include laxity of the capsuloligamentous structures, decreased core and scapular muscle endurance, and scapulothoracic and glenohumeral muscular imbalance; screening tools to assess these components and eventually minimize the role these factors play in overall injury risk for swimmers may be helpful. Currently, insufficient data exist for upper quarter functional testing in swimmers. Additional upper quarter functional testing may further explain the possible sex-related characteristics associated with injury disparity. Effective and functional upper quarter testing could be used to help develop offseason and dry-land training programs focused on performance enhancement and injury prevention.^12,13Swimming requires a significant amount of upper body and core strength, endurance,^11,14 and shoulder mobility and stability.⁵ Although a number of tests have been designed to assess upper quarter function, few tests assess upper quarter stability at the limit of closed chain stability,^15–18 which has been associated with performance enhancement and injury prevention in swimmers.^12,13 The upper quarter Y balance test (YBT-UQ) can be conducted in the field setting with minimal equipment and examines the unilateral performance of the upper quarter at the end range of the athlete''s ability to maintain stability.^15–18 The YBT-UQ challenges the core and upper quarter strength, stability, and mobility that are required for the performance demands of swimming.^13,16,18 The YBT-UQ is a reliable functional test,^16,18 demonstrating a fair to moderate association with several tests that measure core stability (push-up and lateral side bend endurance, range, 0.38–0.45) and upper extremity function (closed kinetic chain upper extremity stability test, range, 0.43–0.49).¹⁸ Current research supports the notion that YBT-UQ performance is not affected by competition level,¹⁹ sex, or limb dominance in active adults¹⁸ and healthy college students.¹⁶ However, performance on the YBT-UQ has yet to be assessed in swimmers, who have different upper quarter demands than previously tested populations.Previous authors³ have shown that female swimmers are at increased risk for injury to the upper quarter compared with their male counterparts. Reasons for this discrepancy are unknown. Basic tests of upper extremity function in athletes, particularly those in sports with significant upper quarter demands, may allow us to identify movement limitations that can be addressed to improve the athlete''s endurance. Such tests may also be beneficial in assessing progress in dry-land training programs aimed at improving swimming performance.¹³ Given the current gaps in the literature, it is beneficial to examine YBT-UQ performance in male and female swimmers to determine if sex differences exist in performance. Based on previous research, we expected no sex difference on the YBT-UQ.^16,18     

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.     

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.     

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.     

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.     

Pain and Effusion and Quadriceps Activation and Strength

Context:

Quadriceps dysfunction is a common consequence of knee joint injury and disease, yet its causes remain elusive.

Objective:

To determine the effects of pain on quadriceps strength and activation and to learn if simultaneous pain and knee joint effusion affect the magnitude of quadriceps dysfunction.

Design:

Crossover study.

Setting:

University research laboratory.

Patients or Other Participants:

Fourteen (8 men, 6 women; age = 23.6 ± 4.8 years, height = 170.3 ± 9.16 cm, mass = 72.9 ± 11.84 kg) healthy volunteers.

Intervention(s):

All participants were tested under 4 randomized conditions: normal knee, effused knee, painful knee, and effused and painful knee.

Main Outcome Measure(s):

Quadriceps strength (Nm/kg) and activation (central activation ratio) were assessed after each condition was induced.

Results:

Quadriceps strength and activation were highest under the normal knee condition and differed from the 3 experimental knee conditions (P < .05). No differences were noted among the 3 experimental knee conditions for either variable (P > .05).

Conclusions:

Both pain and effusion led to quadriceps dysfunction, but the interaction of the 2 stimuli did not increase the magnitude of the strength or activation deficits. Therefore, pain and effusion can be considered equally potent in eliciting quadriceps inhibition. Given that pain and effusion accompany numerous knee conditions, the prevalence of quadriceps dysfunction is likely high.Key Words: arthrogenic muscle inhibition, central activation failure, voluntary activation, muscles

Key Points

• Knee pain and effusion resulted in arthrogenic muscle inhibition and weakness of the quadriceps.
• The simultaneous presence of pain and effusion did not increase the magnitude of quadriceps dysfunction.
• To reduce arthrogenic muscle inhibition and improve muscle strength, clinicians should employ interventions that target removing both pain and effusion.

Quadriceps weakness is a common consequence of traumatic knee joint injury^1,2 and chronic degenerative knee joint conditions.^3,4 Arthrogenic muscle inhibition (AMI), a neurologic decline in muscle activation, results in quadriceps weakness and hinders rehabilitation by preventing gains in strength.⁵ The inability to reverse AMI and restore muscle function can lead to decreased physical abilities,⁶ biomechanical deficits,⁷ and possibly reinjury.⁵ Furthermore, researchers^8,9 have suggested that quadriceps weakness resulting from AMI may place patients at risk for developing osteoarthritis in the knee. In light of the substantial influence of quadriceps AMI on these clinically relevant outcomes, we need to improve our understanding of the factors that contribute to this neurologic decline in muscle activity so efforts to target and reverse it can be implemented and gains in strength can be achieved more easily.Joint injury and disease are accompanied by numerous sequelae (ie, pain, swelling, tissue damage, inflammation), so ascertaining which one ultimately leads to neurologic muscle dysfunction is difficult. Whereas a joint effusion can result in AMI,^10–12 the effects of pain are less understood despite many clinicians attributing AMI to pain. Using techniques that introduce knee pain without accompanying injury may provide insights into the role of pain in eliciting AMI.The degree of knee joint damage may play a role in the quantity of AMI that manifests. Hurley et al^13,14 demonstrated that quadriceps AMI, measured using an interpolated-twitch technique, was greater in patients with extensive traumatic knee injury (eg, fractured tibial plateau, ruptured medial collateral ligament, and medial meniscectomy) than patients with isolated joint trauma (ie, isolated anterior cruciate ligament [ACL] rupture). Similarly, patients with more knee joint symptoms (ie, greater number of symptoms and increased severity of symptoms) may present with greater magnitudes of quadriceps inhibition. Recently, investigators¹⁵ have suggested that patients with more pain display less quadriceps strength, supporting this tenet. Given that effusion and pain often present simultaneously with joint injuries and diseases, such as ACL injury and osteoarthritis, examining both the isolated and cumulative effects of these sequelae appears warranted to determine if they influence the magnitude of muscle inhibition.Experimental joint-effusion and pain models are safe and effective experimental methods that allow for the isolated examination of their effects on muscle function. The effusion model, whereby sterile saline is injected directly into the knee joint capsule,⁷ produces a clinically relevant magnitude of the joint effusion that may be present with traumatic injury. Effusion is thought to activate group II afferents responding to stretch or pressure,^16–18 which in turn may facilitate group Ib interneurons and result in quadriceps AMI.⁵ The pain model involves injecting hypertonic saline into the infrapatellar fat pad to produce anteromedial knee pain similar to that described in patients with patellofemoral pain syndrome.¹⁹ Pain is considered to initiate AMI through activation of group III and IV afferents that act as nocioceptors to signal damage or potential damage to joint structures.^16–18 The firing of these afferents then may lead to facilitation of group Ib interneurons, the flexion reflex, or the gamma loop, ultimately resulting in quadriceps inhibition.²⁰ Thus, these models allow us to create symptoms that are associated with knee injury and have the added benefit of providing a way to examine their effects in isolation.Therefore, the purpose of our study was to determine the effects of pain on quadriceps strength and activation and to learn if simultaneous pain and knee joint effusion would affect the magnitude of quadriceps dysfunction. We hypothesized that pain alone would result in quadriceps inhibition and that the magnitude of inhibition would be greater when effusion and pain were present simultaneously.     

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

Context:

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

Objective:

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

Design:

Cross-sectional study.

Setting:

Training facility of the Israel Defense Forces.

Patients or Other Participants:

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

Intervention(s):

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

Main Outcome Measure(s):

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

Conclusions:

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

Key Points

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

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

Customized Noise-Stimulation Intensity for Bipedal Stability and Unipedal Balance Deficits Associated With Functional Ankle Instability

Context:

Stochastic resonance stimulation (SRS) administered at an optimal intensity could maximize the effects of treatment on balance.

Objective:

To determine if a customized optimal SRS intensity is better than a traditional SRS protocol (applying the same percentage sensory threshold intensity for all participants) for improving double- and single-legged balance in participants with or without functional ankle instability (FAI).

Design:

Case-control study with an embedded crossover design.

Setting:

Laboratory.

Patients or Other Participants:

Twelve healthy participants (6 men, 6 women; age = 22 ± 2 years, height = 170 ± 7 cm, mass = 64 ± 10 kg) and 12 participants (6 men, 6 women; age = 23 ± 3 years, height = 174 ± 8 cm, mass = 69 ± 10 kg) with FAI.

Intervention(s):

The SRS optimal intensity level was determined by finding the intensity from 4 experimental intensities at the percentage sensory threshold (25% [SRS₂₅], 50% [SRS₅₀], 75% [SRS₇₅], 90% [SRS₉₀]) that produced the greatest improvement in resultant center-of-pressure velocity (R-COPV) over a control condition (SRS₀) during double-legged balance. We examined double- and single-legged balance tests, comparing optimal SRS (SRS_opt1) and SRS₀ using a battery of center-of-pressure measures in the frontal and sagittal planes.

Main Outcome Measure(s):

Anterior-posterior (A-P) and medial-lateral (M-L) center-of-pressure velocity (COPV) and center-of-pressure excursion (COPE), R-COPV, and 95th percentile center-of-pressure area ellipse (COPA-95).

Results:

Data were organized into bins that represented optimal (SRS_opt1), second (SRS_opt2), third (SRS_opt3), and fourth (SRS_opt4) improvement over SRS₀. The SRS_opt1 enhanced R-COPV (P ≤ .05) over SRS₀ and other SRS conditions (SRS₀ = 0.94 ± 0.32 cm/s, SRS_opt1 = 0.80 ± 0.19 cm/s, SRS_opt2 = 0.88 ± 0.24 cm/s, SRS_opt3 = 0.94 ± 0.25 cm/s, SRS_opt4 = 1.00 ± 0.28 cm/s). However, SRS did not improve R-COPV over SRS₀ when data were categorized by sensory threshold. Furthermore, SRS_opt1 improved double-legged balance over SRS₀ from 11% to 25% in all participants for the center-of-pressure frontal- and sagittal-plane assessments (P ≤ .05). The SRS_opt1 also improved single-legged balance over SRS₀ from 10% to 17% in participants with FAI for the center-of-pressure frontal- and sagittal-plane assessments (P ≤ .05). The SRS_opt1 did not improve single-legged balance in participants with stable ankles.

Conclusions:

The SRS_opt1 improved double-legged balance and transfers to enhancing single-legged balance deficits associated with FAI.Key Words: chronic ankle instability, noise, postural stability, therapy

Key Points

• Stochastic resonance stimulation can be considered an alternative treatment for balance impairments.
• Stochastic resonance stimulation may be an effective treatment in the early stages of rehabilitation to facilitate immediate balance improvements that may help patients transition to complex postural stability exercises or functional movements.
• A double-legged balance-optimization protocol may be an efficient method to determine a customized optimal stochastic resonance stimulation intensity that will transfer to improving single-legged balance for functional ankle instability.

Functional ankle instability (FAI) is a residual symptom of ankle sprains that often causes the sensation of “giving way” at the ankle and recurrent ankle sprains.¹ In addition, sensorimotor deficits associated with FAI are present as balance impairments.² Postural instabilities are important to identify because poor balance is a predisposing factor of ankle sprain injury.^3–5 Given that balance improvements associated with rehabilitation often take 6 weeks to occur,^6,7 a therapy, such as stochastic resonance stimulation (SRS), that facilitates balance improvements immediately⁸ or more quickly than rehabilitation alone^9,10 would be beneficial for individuals with FAI. Stochastic resonance stimulation is a therapy that introduces subsensory mechanical noise through the skin to enhance the ability of mechanoreceptors to detect and transmit weak signals related to balance.^11–13Natural noise created in the body can promote signal detection by amplifying weak sensory signals.^14,15 This natural noise occurs from external stimuli, physiologic processes, and biomechanics.^14,15 However, this internally generated noise may not be at a high enough level in some individuals to improve signal detection.^14,15 Healthy and injured individuals may benefit from SRS therapy when the level of naturally occurring noise is too low to facilitate signal detection.^14,15 Most evidence has indicated that individuals with and without sensorimotor impairments react similarly to SRS,^9,10,16–20 suggesting that the level of natural noise in the body is low enough for SRS to have positive treatment effects.Interestingly, however, Priplata et al¹⁸ reported that elderly participants had a better response to SRS than young healthy participants because the former used SRS to facilitate sensory signal detection to reduce sway. In addition, SRS improved balance in the elderly participants to within the normal range for young, healthy participants.¹⁸ Sensorimotor impairments are associated with age, and the naturally occurring noise in the elderly participants might not have contributed to signal detection.¹⁸ Thus, SRS corrected these sensorimotor deficits to facilitate balance improvements.¹⁸ Given the findings in the elderly participants,¹⁸ we postulate that the balance response to SRS might be better in individuals with FAI than in healthy individuals because FAI also is associated with sensorimotor deficits. Currently, no evidence exists to demonstrate that SRS produces better balance for FAI than stable ankles. Demonstrating that SRS improves balance more in FAI than stable ankles lends credence to the notion that this therapy enhances sensorimotor function.Recent evidence²¹ has indicated that the sensorimotor dysfunction with FAI may be due to reflex depressions, which can cause excessive sway with single-legged balance. These poor postural reflexes can result from an inability to integrate afferent input and efferent output.²² That is, diminished sensation from the foot and ankle may not detect signals related to postural control, leading to inappropriate muscle contractions that maintain stability. The inability to sense signals to generate adequate postural reflexes suggests that the naturally occurring internal noise is at a level too low to facilitate signal detection. To correct this sensorimotor impairment, SRS can serve as a pedestal to predispose mechanoreceptors to fire in the presence of real sensory signals, especially signals that otherwise would be undetectable.^11–13The traditional method for examining the effects of SRS on balance improvements is to apply the same subsensory intensity to all participants within a research study.^16–20 Subsensory intensities from 25% to 90% have enhanced balance in patients who are healthy, have diabetes, or have had a stroke.^16–20 Researchers¹⁷ also have presented preliminary data indicating that 75% of sensory threshold could be the optimal SRS intensity to affect the degree of balance improvements. This finding was confirmed in a second experiment¹⁷ when this specific SRS intensity was applied to all participants to optimize balance enhancements.Two research groups recently have proposed customizing the intensity of SRS applied to an individual to maximize treatment effects in lieu of applying the same intensity to all participants.^8,23 The rationale for this customized design was deduced from the early work of Collins et al,²⁴ who demonstrated that performance increased to a peak with increasing levels of SRS intensity and then decreased; however, the SRS intensity associated with this optimal intensity was slightly different for participants. In other words, the levels of SRS intensity for improving sensorimotor function must be fine tuned because subsensory intensities that are too low may not improve balance and those that are too high can diminish function.^{8,11,17,23,24} Furthermore, a customized SRS intensity is proposed for minimizing random error in datasets, potentially decreasing washout effects in a group analysis.⁸ Specifically related to FAI, researchers⁸ using 1 of 2 input SRS intensities have demonstrated that 92% of participants with FAI improved their single-legged balance with at least 1 input intensity, whereas 55% of them had impaired balance at the other input intensity. This finding suggests that using 1 intensity for all participants may have masked the treatment effects of SRS if the intensity that impaired balance was used for analysis.⁸ More recently, Mulavara et al²³ found that customizing the SRS intensity applied to an individual was crucial for maximizing balance improvements in healthy participants. These researchers defined an optimal intensity as the stimulus amplitude emitted from the SRS device that best improved balance over a control (no-SRS) condition.²³ By determining this customized optimal intensity for each individual, we speculate that treatment effects associated with SRS will increase compared with the same intensity for all participants.Double-legged balance tests are recommended for determining the treatment effects of SRS on stability.^16–20,23 These bipedal assessments allow individuals to maximize their stability with a wide base of support, providing a reliable means of determining the optimal SRS intensity. This recommended double-legged SRS protocol has not been tested in participants with FAI. Clinically, this protocol may be important to examine with FAI because balance can be assessed quickly when optimizing SRS intensity. Single-legged balance protocols may not be efficient for optimizing SRS intensity because of the number of unsuccessful trials associated with FAI. However, most researchers do not use single-legged balance as a criterion standard for assessing balance deficits associated with FAI² or quantifying treatment effects of SRS on FAI.^8–10 Therefore, for clinical applications, we propose using a double-legged balance protocol to quickly and efficiently optimize SRS intensity and then using this intensity to enhance single-legged balance. This optimization protocol may be more clinically relevant if the intensity for enhancing double-legged balance transfers to improving single-legged balance.Along these lines of clinical effectiveness, we believe that clinicians need to focus on 1 balance outcome measure when optimizing SRS intensity to improve stability. Common balance outcome measures that have improved with SRS over control conditions include sway velocity, excursion, and area.^16–20 Specifically related to FAI, resultant center-of-pressure velocity (COPV) has been used to assess the immediate effects of SRS on single-legged balance.⁸ Other balance measures also have been examined with SRS in participants with FAI, but all use center-of-pressure excursion (COPE) data points to compute the outcome measures (eg, COPV is computed by dividing excursion by time).^9,10 For clinical applicability, we have taken a minimalist approach in our study by selecting resultant COPV as our main outcome measure for the optimization protocol because it has detected balance improvements associated with SRS in participants with FAI.⁸Therefore, the initial purpose of our study was to determine if a customized optimal SRS intensity was better than a traditional SRS protocol (applying the same percentage sensory threshold intensity for all participants) for improving double- and single-legged balance in participants with and without FAI. Using a customized optimal SRS intensity, we wanted to determine (1) if individuals with FAI and individuals with stable ankles responded at different rates, (2) if double-legged balance (as measured by additional center-of-pressure measures) improved more with the optimal intensity than a control condition, and (3) if the optimal intensity for double-legged balance could transfer to improving single-legged balance over a control condition. Our hypotheses included the following: (1) The customized optimal SRS intensity protocol would improve double-legged balance better than the traditional protocol; (2) the treatment response to optimal SRS would be greater in individuals with FAI than in individuals with stable ankles; (3) the optimal intensity would improve double-legged balance more than a control condition; and (4) the optimal intensity would transfer to improving single-legged balance more than a control condition. The results of our study may be clinically relevant because a customized optimal SRS intensity level that maximally improves balance may enhance rehabilitation outcome measures and lead to greater ankle stability.     

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.     

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.     

Strength and Jump Biomechanics of Elite and Recreational Female Youth Soccer Players

Context

Most researchers investigating soccer injuries have studied elite athletes because they have greater athletic-exposure hours than other athletes, but most youth participate at the recreational level. If risk factors for injury vary by soccer level, then recommendations generated using research with elite youth soccer players might not generalize to recreational players.

Objective

To examine injury risk factors of strength and jump biomechanics by soccer level in female youth athletes and to determine whether research recommendations based on elite youth athletes could be generalized to recreational players.

Design

Cross-sectional study.

Setting

Seattle Youth Soccer Association.

Patients or Other Participants

Female soccer players (N = 92) aged 11 to 14 years were recruited from 4 randomly selected elite (n = 50; age = 12.5 years, 95% confidence interval [95% CI]) = 12.3, 12.8 years; height = 157.8 cm, 95% CI = 155.2, 160.3 cm; mass = 49.9 kg, 95% CI = 47.3, 52.6 kg) and 4 randomly selected recreational (n = 42; age = 13.2 years, 95% CI = 13.0, 13.5 years; height = 161.1 cm, 95% CI = 159.2, 163.1 cm; mass = 50.6 kg, 95% CI = 48.3, 53.0 kg) soccer teams.

Main Outcome Measure(s)

Players completed a questionnaire about demographics, history of previous injury, and soccer experience. Physical therapists used dynamometry to measure hip strength (abduction, adduction, extension, flexion) and knee strength (flexion, extension) and Sportsmetrics to measure vertical jump height and jump biomechanics. We compared all measurements by soccer level using linear regression to adjust for age and mass.

Results

Elite players were similar to recreational players in all measures of hip and knee strength, vertical jump height, and normalized knee separation (a valgus estimate generated using Sportsmetrics).

Conclusions

Female elite youth players and recreational players had similar lower extremity strength and jump biomechanics. This suggests that recommendations generated from research with elite youth soccer players could be generalized to recreational players.Key Words: muscle strength, children, adolescents, risk factors, athletic injuries

Key Points

• Lower extremity strength and jump biomechanics were similar for elite and recreational female soccer players aged 11 to 14 years.
• Recommendations from research on elite youth soccer players should generalize to recreational players.

Soccer is the fifth most popular sport in the United States,¹ with an estimated 8.6 million players from 6 to 11 years of age and 5 million players from 12 to 17 years of age.² Most of these players participate at the recreational (nonelite) level, but most researchers studying injuries have focused on elite athletes.^3–7 Researchers more commonly study elite athletes because they participate year-round and thus have greater athletic-exposure hours and more opportunity for injury. If elite and recreational players differ in terms of potential risk factors for injury, recommendations developed using research with elite athletes might not generalize to recreational players.Data have suggested that adult elite soccer players are stronger than nonelite players.^8,9 Cometti et al⁸ reported greater knee-flexion (hamstrings) strength in elite than nonelite soccer players, and Oberg et al⁹ reported that elite players were stronger in both knee flexion and extension. These differences in strength could result in altered risk of injury because hamstrings weakness is thought to increase susceptibility to anterior cruciate ligament (ACL) tears.^10,11 However,^12,13 researchers evaluating strength by soccer level in youth have not found differences in lower extremity strength. Whereas Hansen et al¹² found differences by soccer level in hand grip and back strength of youth players, they did not find differences in quadriceps strength. In a similar study, le Gall et al¹³ reported no differences in quadriceps or hamstrings strength by soccer level in youth. To our knowledge, no one has compared strength by soccer level in female youth athletes.Jump biomechanics, particularly valgus knee alignment on landing, have been shown to be a risk factor for knee injury because they place undue stress on the ACL.¹⁴ Investigators¹⁵ have suggested that poor jump biomechanics could contribute to the increased risk of ACL injury in female athletes, who more commonly exhibit valgus knee alignment during jumping maneuvers than male athletes. Researchers^16–19 have evaluated vertical jump height by soccer level, but to our knowledge, none have examined differences in valgus alignment by soccer level in the adult or youth population.Although researchers have found that adult soccer players designated as elite and recreational differ in strength and jump biomechanics,^8,9,16–19 few have compared these characteristics by soccer level in the youth population, and to our knowledge, none have studied female youth. Therefore, the purpose of our study was to examine strength and jump biomechanics by soccer level in female youth athletes to determine whether research recommendations based on elite youth athletes could be generalized to recreational players.     

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

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

Key Points

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

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