The MyJump App is a Valid Method of Assessing and Classifying Limb Symmetry During Recovery from Anterior Cruciate Ligament Reconstruction

# Background Jump testing performance and limb symmetry measures are important metrics for clinicians to monitor during rehabilitation after Anterior Cruciate Ligament (ACL) reconstruction, however they require hardware and software which is not commonly available in clinical practice. Video-based solutions may present a feasible alternative, but their veracity in classifying patients using limb-symmetry of 90% has not been established, nor have the clinimetric values for the performance measures been reported in this population. # Purpose To describe the diagnostic accuracy (pass/fail using 90% LSI) and clinimetrics of an iPad-based app ("MyJump") compared to reference force plate analyses for limb symmetry, jump/hop height, contact time, flight time, and reactive strength index # Study design Prospective cohort, diagnostic accuracy # Methods Fifty-one consecutive patients recovering from ACL reconstruction undertaking routine independent clinical evaluation of their hop and jump performance were concurrently and independently examined using force plates and the MyJump app. Diagnostic accuracy of MyJump was compared to reference force plate analyses using a criterion of 90% limb symmetry. # Results Diagnostic accuracy of the MyJump app was very good: positive predictive value for jump height was 0.83 and 1.0 for reactive strength index, and negative predictive value was 0.95 and 1.0 for the same metrics, respectively. Of the 131 classifications made using the MyJump app, there were five false positives and three false negatives -- all of these were in classification of jump height with no misclassifications of RSI. Irrespective of jump type, the MyJump app displayed excellent reliability (ICC\>0.95) for both height and reactive strength index. Minimum detectable changes were approximately 1cm for height, 0.1 for reactive strength index, 0.02s for contact time, and 0.3s for flight time. # Conclusion Where force plates are unavailable, the MyJump app is a valid and reliable substitute for criteria assessment of jump/hop height and reactive strength index in those recovering from ACL surgery using a 90% limb symmetry threshold. The minimum detectable changes vary by metric but are likely sufficiently accurate to detect clinical changes. # Level Of Evidence Level

Single leg drop jump is affected by physical capacities in male soccer players following ACL reconstruction

Single leg drop jump (SLDJ) assessment is commonly used during the later stages of rehabilitation to identify residual deficits in reactive strength but the effects of physical capacity on kinetic and kinematic variables in male soccer players following ACL reconstruction remain unknown. Isokinetic knee extension strength, kinematics from an inertial measurement unit 3D system and SLDJ performance variables and mechanics derived from a force plate were measured in 64 professional soccer players (24.7 ± 3.4 years) prior to return to sport (RTS). SLDJ between-limb differences was measured (part 1) and players were divided into tertiles based on isokinetic knee extension strength (weak, moderate and strong) and reactive strength index (RSI) (low, medium and high) (part 2). Moderate to large significant differences between the ACL reconstructed and uninjured limb in SLDJ performance (d = 0.92–1.05), kinetic (d = 0.62–0.71) and kinematic variables (d = 0.56) were evident. Stronger athletes jumped higher (p = 0.002; d = 0.85), produced greater concentric (p = 0.001; d = 0.85) and eccentric power (p = 0.002; d = 0.84). Similar findings were present for RSI, but the effects were larger (d = 1.52–3.84). Weaker players, and in particular those who had lower RSI, displayed landing mechanics indicative of a ‘stiff’ knee movement strategy. SLDJ performance, kinetic and kinematic differences were identified between-limbs in soccer players at the end of their rehabilitation following ACL reconstruction. Players with lower knee extension strength and RSI displayed reduced performance and kinetic strategies associated with increased injury risk

A comparison of strength and power characteristics prior to anterior cruciate ligament rupture and at the end of rehabilitation in professional soccer players

Background: Strength and power is often reduced on the involved vs. contralateral limb and healthy controls following anterior cruciate ligament (ACL) reconstruction but no study has compared to pre-injury values at the time of return to sport (RTS). Hypothesis: Divergent recovery patterns in strength and power characteristics will be present at RTS relative to pre-injury baseline data and healthy matched controls.\ud Study design: Cohort study Level of evidence: Level 3 Methods: Isokinetic strength tests, bilateral and single leg countermovement jumps (CMJ; SLCMJ) were measured prior to ACL rupture in 20 professional soccer players. These then had surgical reconstruction (ACL group) and completed follow up testing prior to RTS. Healthy controls (uninjured group) were tested at the same time as the ACL group pre-injury. Values recorded at RTS of the ACL group were compared to pre-injury. We also compared the uninjured and ACL groups at baseline and RTS. Results: Compared to pre-injury, ACL normalised quadriceps peak torque of the involved limb (% difference = -7%), SLCMJ height (% difference = -12.08%) and Reactive Strength Index modified (RSImod) (% difference = -5.04%) were reduced following ACL reconstruction. No significant reductions in CMJ height, RSImod and relative peak power were indicated at RTS in the ACL group when compared to pre-injury values but deficits were present relative to controls. The uninvolved limb significantly improved quadriceps (% difference = 9.34%) and hamstring strength (% difference = 7.36%) from pre-injury to RTS. No significant differences from baseline were shown in SLCMJ height, power and reactive strength of the uninvolved limb following ACL reconstruction. Conclusion: Strength and power in professional soccer players at RTS following ACL reconstruction were often reduced compared to preinjury values and matched healthy controls. Clinical relevance: Deficits were more apparent in the SLCMJ suggesting dynamic and multijoint unilateral force production is an important component of rehabilitation. Use of the uninvolved limb and normative data to determine recovery may not always be appropriate

Comparison of strength and power characteristics before ACL rupture and at the end of rehabilitation before return to sport in professional soccer players

Background: Strength and power is often reduced on the involved versus contralateral limb and healthy controls after anterior cruciate ligament (ACL) reconstruction, but no study has compared with preinjury values at the time of return to sport (RTS). Hypothesis: Divergent recovery patterns in strength and power characteristics will be present at RTS relative to preinjury baseline data and healthy matched controls. Study design: Cohort study. Level of evidence: Level 3. Methods: Isokinetic strength tests, bilateral and single-leg countermovement jumps (CMJ; SLCMJ) were measured before ACL rupture in 20 professional soccer players. These then had surgical reconstruction (ACL group) and completed follow-up testing before RTS. Healthy controls (uninjured group) were tested at the same time as the ACL group preinjury. Values recorded at RTS of the ACL group were compared with preinjury. We also compared the uninjured and ACL groups at baseline and RTS. Results: Compared with preinjury, ACL normalized quadriceps peak torque of the involved limb (difference = -7%), SLCMJ height (difference = -12.08%), and Reactive Strength Index modified (RSImod) (difference = -5.04%) were reduced after ACL reconstruction. No significant reductions in CMJ height, RSImod, and relative peak power were indicated at RTS in the ACL group when compared with preinjury values, but deficits were present relative to controls. The uninvolved limb improved quadriceps (difference = 9.34%) and hamstring strength (difference = 7.36%) from preinjury to RTS. No significant differences from baseline were shown in SLCMJ height, power, and reactive strength of the uninvolved limb after ACL reconstruction. Conclusion: Strength and power in professional soccer players at RTS after ACL reconstruction were often reduced compared with preinjury values and matched healthy controls. Clinical relevance: Deficits were more apparent in the SLCMJ, suggesting that dynamic and multijoint unilateral force production is an important component of rehabilitation. Use of the uninvolved limb and normative data to determine recovery may not always be appropriate

The acute effects of assisted or resisted variable resistance back squat exercise on countermovement jump performance

INTRODUCTION: Back squat warm-up activities using elastic band (EB) resistance in combination with free weight resistance (FWR) can improve subsequent countermovement jump (CMJ) performance [1], a phenomenon termed post-activation performance enhancement (PAPE). However, across the literature sub-maximal loads of 85% are commonly used, with limited research existing on the effect of lighter loads on acute performance enhancement under both FWR or EB (resisted [RES] or assisted [ASS]) conditions. The aim of the present study was to compare the effects of back squats at 50% 1-RM under two EB attachment sites (ASS and RES) and FWR alone after a task-specific comprehensive warm-up on subsequent CMJ performance. METHODS: Twenty active males (age = 24.9±3.7 y, height = 1.7±5.7 m, mass = 83.4±12.6 kg) volunteered for the study and completed three separate experimental conditions (FWR, RES, ASS) separated by 48 h following a randomised crossover design. During each condition, participants first completed initial baseline CMJ tests (BL1) followed by a task-specific comprehensive warm-up that involved 5 min of cycling, two sets of 5 bodyweight squats, 5 continuous CMJs at 70% of perceived maximum, and finally, maximal CMJs every 30 s until 3 consecutive jumps were within 3% of jump height. Baseline 2 (BL2) CMJ tests were then completed and followed by 3 back squats following either the FWR, RES or ASS protocols at 50% 1-RM with 35% of the load generated by EBs during the RES and ASS conditions. CMJs were then performed 30 s, 4 min, 8 min and 12 min later. RESULTS: Significant increases (p<0.05) in both jump height (4.6-18.8%) and peak power (5.3-10.8%) were observed across all timepoints when compared with BL1 measure in all conditions. In the ASS condition, significant increases in jump height (4.6-11.8%) and peak power (6.5-2.0%) were observed at 30 s, 4 min, 8 min, and 12 min compared to BL2. In the RES condition, significant increases in jump height (7.1-1.2%) and peak power (2.3-5.4%) were observed at 30 s, 4 min, and 8 min, and in the FWR condition, significant increases in jump height (2.2-5.7%) and peak power (1-4.6%) were observed at 30 s and 4 min. DISCUSSION: The implementation of back squats into a warm-up activity at 50% 1-RM increased jump performance when EBs were used during both the ASS and RES conditions, with the increase in jump height being greater than that observed in the FWR condition. The use of EB resistance speculatively reduces loading at the sticking point, potentially allowing for greater acceleration during the concentric phase as lower-limb joints extend at the point where more optimal muscle lengths are achieved [2].These data have important implications for warm-up design for strength and power activities. REFERENCES 1. Mina et al. (2019). Scand J Med Sci Sports. 29(3):380-392. 2. Anderson et al. (2008). J Strength Cond Res. 22(2):567-574