Residual Deficits in Reactive Strength After Anterior Cruciate Ligament Reconstruction in Soccer Players.

CONTEXT: Deficits in plyometric abilities are common after anterior cruciate ligament reconstruction (ACLR). Vertical rebound tasks may provide a targeted evaluation of knee function. OBJECTIVE: To examine the utility of a vertical hop test for assessing function after ACLR and establishing factors associated with performance. DESIGN: Cross-sectional study. SETTING: Rehabilitation program. PATIENTS OR OTHER PARTICIPANTS: Soccer players with a history of ACLR (n = 73) and matched control individuals (n = 195). MAIN OUTCOME MEASURE(S): The 10-second vertical hop test provided measures of jump height, the Reactive Strength Index (RSI), and asymmetry. We also examined possible predictors of hop performance, including single-legged vertical drop jump, isokinetic knee-extension strength, and the International Knee Documentation Committee questionnaire score. RESULTS: Between-limbs differences were identified only for the ACLR group, and asymmetry scores increased in those with a history of ACLR (P < .001) compared with the control group. The single-legged vertical drop jump, RSI, and knee-extension torque were significant predictors of 10-second hop height (R2 = 20.1%) and RSI (R2 = 47.1%). CONCLUSIONS: Vertical hop deficits were present after ACLR, even after participants completed a comprehensive rehabilitation program. This may have been due to reduced knee-extension and reactive strength. Vertical hop tests warrant inclusion as part of the return-to-sport test battery.

Repetitions in Reserve Is a Reliable Tool for Prescribing Resistance Training Load.

ABSTRACT: Lovegrove, S, Hughes, L, Mansfield, S, Read, P, Price, P, and Patterson, SD. Repetitions in reserve is a reliable tool for prescribing resistance training load. J Strength Cond Res 36(10): 2696-2700, 2022-This study investigated the reliability of repetitions in reserve (RIR) as a method for prescribing resistance training load for the deadlift and bench press exercises. Fifteen novice trained men (age: 17.3 ± 0.9 years, height: 176.0 ± 8.8 cm, body mass: 71.3 ± 10.7 kg) were assessed for 1 repetition maximum (1RM) for deadlift (118.1 ± 27.3 kg) and bench press (58.2 ± 18.6 kg). Subsequently, they completed 3 identical sessions (one familiarization session and 2 testing sessions) comprising sets of 3, 5, and 8 repetitions. For each repetition scheme, the load was progressively increased in successive sets until subjects felt they reached 1-RIR at the end of the set. Test-retest reliability of load prescription between the 2 testing sessions was determined using intraclass correlation coefficient (ICC) and coefficient of variation (CV). A 2-way analysis of variance with repeated measures was used for each exercise to assess differences in the load corresponding to 1-RIR within each repetition scheme. All test-retest comparisons demonstrated a high level of reliability (deadlift: ICC = 0.95-0.99, CV = 2.7-5.7% and bench press: ICC = 0.97-0.99, CV = 3.8-6.2%). Although there were no differences between time points, there was a difference for load corresponding to 1-RIR across the 3 repetition schemes (deadlift: 88.2, 84.3, and 79.2% 1RM; bench press: 93.0, 87.3, and 79.6% 1RM for the 3-, 5-, and 8-repetition sets, respectively). These results suggest that RIR is a reliable tool for load prescription in a young novice population. Furthermore, the between-repetition scheme differences highlight that practitioners can effectively manipulate load and volume (repetitions in a set) throughout a training program to target specific resistance training adaptations.

Biomechanical Analysis of the Tuck Jump Assessment.

ABSTRACT: Nascimento, N, Sideris, V, and Read, PJ. Biomechanical analysis of the tuck jump assessment. J Strength Cond Res 36(10): 2946-2949, 2022-The tuck jump assessment (TJA) examines plyometric technique flaws associated with the increased risk of anterior cruciate ligament injury. Biomechanical data to investigate the mechanics used during the TJA are limited and assessing each jump individually across the entire test period is time inefficient. This study examined performance characteristics and movement mechanics in 16 professional soccer players during a standardized TJA protocol (10 jumps) to determine if sensitive periods exist within the test period (first 5 vs. last 5). Jump height, average power (PW) reactive strength index (RSI), frontal plane projection angle (FPPA), knee angular velocity (AV), and peak knee flexion angle (PKA) were analyzed using an optoelectrical and inertial measurement unit device. Jump height and PW increased in the past 5 jumps displaying a medium effect size (d = > 0.5). A trend was observed of increased AV, FPPA, and PKA during the past 5 jumps; however, no meaningful differences were observed between respective jump phases, and effect sizes were small (d ≤ 0.2). This study indicates that performance metrics increase during the past 5 jumps of a standardized TJA 10-jump protocol; thus, analyzing the entire test period may not be required, providing a time-efficient approach. Caution should be applied if using this protocol as an injury risk screening tool or to identify fatigue related alterations in male professional soccer players as no obvious movement abnormalities were apparent and minimal differences were present between jump phases in a range of kinematic variables across the recorded test duration.

The Acute Effects of Accentuated Eccentric Loading on Drop Jump Kinetics in Adolescent Athletes.

ABSTRACT: Lloyd, RS, Howard, SW, Pedley, JS, Read, PJ, Gould, ZI, and Oliver, JL. The acute effects of accentuated eccentric loading on drop jump kinetics in adolescent athletes. J Strength Cond Res 36(9): 2381-2386, 2022-The purpose of the study was to determine the acute effects of accentuated eccentric loading (AEL) on drop jump kinetics in adolescent athletes. Fifteen male rugby players (mean ± SD: age = 16.2 ± 1.01, body mass = 73.38 ± 9.94, and height = 178.91 ± 6.74) completed 3 trials of a drop jump with and without an accentuated eccentric load using a dumbbell release technique that equated to 15% body mass. The addition of the AEL stimulus resulted in significant, moderate increases in jump height (p < 0.05; Wilcoxon r = 0.47) and braking and propulsive impulse (p < 0.05, Hedges' g = 0.43; p < 0.05, g = 0.61, respectively) but did not significantly influence reactive strength index. Concurrently, there were significant, moderate increases in ground contact times (p < 0.05; r = 0.45) and reductions in spring-like correlations (p < 0.05; g = 0.94). Neither the magnitude nor timing of peak landing force were significantly altered in the AEL protocol (p < 0.05, g = 0.38; p < 0.05, r = 0.10, respectively). Cumulatively, these data indicate that implementation of AEL resulted in meaningful improvements in jump height, driven by significant increases in braking and propulsive impulse. Despite extensions in ground contact times and reductions in spring-like behavior, neither peak landing force nor time to peak force were negatively altered by the AEL. These results indicate that adolescent athletes can realize superior vertical jump heights during drop jumps using AEL, without displaying marked changes in the magnitude or timing of peak landing force.

Impaired Stretch-Shortening Cycle Function Persists Despite Improvements in Reactive Strength After Anterior Cruciate Ligament Reconstruction.

ABSTRACT: Read, PJ, Pedley, JS, Eirug, I, Sideris, V, and Oliver, JL. Impaired stretch-shortening cycle function persists despite improvements in reactive strength followingafter anterior cruciate ligament reconstruction. J Strength Cond Res 36(5): 1238-1244, 2022-Reactive strength index (RSI) during a single-leg drop jump (SLDJ) has been indicated to determine return-to-sport readiness after anterior cruciate ligament (ACL) reconstruction, but only cross-sectional studies are available. Ground reaction force data and characterization of stretch-shortening cycle (SSC) function also remain sparse. Single-leg drop jump performance, ground reaction force, and SSC function were examined in soccer players with ACL reconstruction (n = 26) and matched controls (n = 25). Injured players were tested at 2 time points (32 and 42 weeks postsurgery). Stretch-shortening cycle function was classified as good (no impact peak and spring like), moderate (impact peak but still spring like or no impact peak and not spring like), or poor (impact peak and not spring like). The involved limb displayed lower-jump height, poorer RSI, less spring-like behavior, earlier peak landing force, and a greater ratio of landing peak to take-off peak force compared with the uninvolved limb and controls at the initial assessment (p < 0.001). Proportionally, more involved limbs were categorized as poor or moderate at the initial assessment (69.2%) and follow-up (50%) in comparison with the control limbs (14%). The reactive strength index was the only variable to change significantly between the initial assessment and follow-up on the involved limb (p < 0.05). No changes in the proportion of ACL reconstructed individuals categorized as poor or moderate SSC function at the follow-up assessment were observed. Residual deficits are present in SLDJ performance, SSC function, and ground reaction force characteristics after ACL reconstruction. The reactive strength index should not be the sole metric, as observed increases did not correspond with changes in SSC function.

The use of wearable technology as an assessment tool to identify between-limb differences during functional tasks following ACL reconstruction. A scoping review.

OBJECTIVE: To report how wearable sensors have been used to identify between-limb deficits during functional tasks following ACL reconstruction and critically examine the methods used. METHODS: We performed a scoping review of studies including participants with ACL reconstruction as the primary surgical procedure, who were assessed using wearable sensors during functional movement tasks (e.g., balance, walking or running, jumping and landing) at all postsurgical time frames. RESULTS: Eleven studies met the inclusion criteria. The majority examined jumping-landing tasks and reported kinematic and kinetic differences between limbs (involved vs. unninvolved) and groups (injured vs. controls). Excellent reliability and moderate-strong agreement with laboratory protocols was indicated, with IMU sensors providing an accurate estimation of kinetics, but the number of studies and range of tasks used were limited. Methodological differences were present including, sensor placement, sampling rate, time post-surgery and type of assessment which appear to affect the outcome. CONCLUSIONS: Wearable sensors consistently identified between-limb and group deficits following ACL reconstruction. Preliminary evidence suggests these technologies could be used to monitor knee function during rehabilitation, but further research is needed including, validation against criterion measures. Practitioners should also consider how the methods used can affect the accuracy of the outcome.

Angle specific analysis of hamstrings and quadriceps isokinetic torque identify residual deficits in soccer players following ACL reconstruction: a longitudinal investigation.

 Analysing the isokinetic curve is important following ACL reconstruction as there may be deficits in torque production at specific points throughout the range of motion. We examined isokinetic (60°.s-1) torque-angle characteristics in 27 male soccer players (24.5 ± 3.9 years) at 3 time-points (17 ± 5; 25 ± 6; and 34 ± 7 weeks post-surgery). Extracted data included knee flexor and extensor peak torque, conventional hamstrings: quadriceps (H/Q) ratio, and angle-specific torque using Statistical Parametric Mapping (SPM). There were significant involved limb increases in extension peak torque at each assessment (p<0.001); however, asymmetry favouring the un-involved limb was observed (p<0.01). Flexion peak torque was greater on the un-involved limb at assessments 1 and 2 only (p<0.05). The angle of peak torque was not significantly different at individual time-points or within-limbs across the 3 assessments. SPM revealed involved limb angle-specific reductions in extension torque across the full range of motion at time-points 1 and 2 (p<0.001) but only in angles [51-80°] at assessment 3 (p<0.05). Between limb H/Q angle differences [33-45°] were shown at assessments 2 and 3. The ratio ranged from 1.60-0.74 depending on the angle tested. Angle-specific moment curves are useful for monitoring patterns of strength development during rehabilitation.

Effects of a 10-Month Neuromuscular Training Program on Strength, Power, Speed, and Vault Performance in Young Female Gymnasts.

PURPOSE: This study aimed to evaluate a 10-month neuromuscular training (NMT) intervention on isometric and dynamic kinetics, standing long jump (SLJ) distance, speed, and sport-specific performance. METHODS: Forty-three prepubertal female gymnasts were allocated into either a gymnastics + NMT (gNMT; n = 16), gymnastics only (GYM, n = 15), or maturity-matched control (CON; n = 12) group. The gNMT followed a 10-month, twice-weekly NMT program that targeted movement competency, strength, power, and speed. Vaulting vertical take-off velocity, speed, SLJ distance, and kinetics during an isometric mid-thigh pull (IMTP), countermovement jump (CMJ), and drop jump (DJ) were measured at baseline and thereafter at 4, 7, and 10 months. Within-group differences were calculated using 3 × 4 repeated-measures ANCOVA. RESULTS: Interaction effects were observed for SLJ distance and various IMTP, DJ, and vaulting variables. The gNMT showed significant improvements in IMTP absolute force and SLJ distance after 4 months and each subsequent testing session. IMTP relative force and various CMJ and DJ kinetics significantly improved in the gNMT from 7 months. Significant gains in speed and vaulting take-off velocity occurred after 10 months. The GYM group achieved some significant improvements in CMJ impulse, absolute isometric strength, and DJ spring-like behavior, whereas the CON group did not experience any changes. CONCLUSIONS: The addition of NMT to gymnastics training improved various isometric and dynamic kinetics, SLJ distance, speed, and vaulting take-off velocity in the gNMT, changes that were not equally evidenced for GYM or CON. The threshold for most of the training-induced adaptations observed in IMTP relative force, CMJ and DJ kinetics, sprint speed, and vaulting were achieved after 7 months, emphasizing the efficacy of long-term NMT programs for young gymnasts.

A Novel Method to Categorize Stretch-Shortening Cycle Performance Across Maturity in Youth Soccer Players.

ABSTRACT: Pedley, JS, Lloyd, RS, Read, PJ, Moore, IS, Myer, GD, and Oliver, JL. A novel method to categorize stretch-shortening cycle performance across maturity in youth soccer players. J Strength Cond Res 36(9): 2573-2580, 2022-This study used a novel method to categorize stretch-shortening cycle (SSC) function during a drop jump (DJ) using the force-time curve. This method was then used to determine the effect of maturity status upon SSC function and effect of SSC function on DJ performance. Prepeak, circa-peak, and postpeak height velocity male youth soccer players completed a preseason 30-cm DJ onto a force plate. Stretch-shortening cycle function was categorized as poor (impact peak and not spring-like), moderate (impact peak and spring-like), or good (no impact peak and spring-like). Interactions between SSC function and maturity status, and SSC function and kinetic variables were explored. Youth soccer players displaying good SSC function were older and more mature than those with poor SSC function; however, 9.9% of post peak height velocity still displayed poor SSC function. Players with good SSC function recorded significantly shorter ground contact times, reduced time between peak landing and takeoff force, reduced center of mass displacement, and significantly greater takeoff forces than players with moderate and poor SSC function (all p < 0.05). SSC function during a standardized DJ improves with maturation, but a portion of mature players still demonstrate poor SSC function. Good SSC function was associated with improved DJ outcome measures except jump height. Tailored training interventions based on SSC competency may be required to optimally enhance SSC function.

The Deceleration Deficit: A Novel Field-Based Method to Quantify Deceleration During Change of Direction Performance.

ABSTRACT: Clarke, R, Read, PJ, De Ste Croix, MBA, and Hughes, JD. The deceleration deficit: a novel field-based method to quantify deceleration during change of direction performance. J Strength Cond Res 36(9): 2434-2439, 2022-The study investigated the relationship between linear and change of direction (COD) speed performance components and the individual differences between deceleration deficit (DD) and COD deficit (CODD). Thirty-six subjects (mean ± SD : age = 20.3 ± 2.9 years; stature = 175.2 ± 7.7 cm; and body mass = 78.0 ± 16.7 kg) completed 3 trials of a 505 test in both turning directions (dominant [D]; nondominant [ND]) and 3 15-m linear sprints. Deceleration deficit was calculated by the 15-m approach in the 505 test, minus the athlete's linear 15-m sprint time. To compare individuals CODD and DD, z-scores were calculated, and moderate worthwhile changes (MWCs) were identified between these deficit z-scores. Significant correlations were identified between linear sprints and 505 time (D: r = 0.71, 0.74; P < 0.01. ND: r = 0.76, 0.75; P < 0.01) for 10-m and 15-m sprint. respectively, and between 505 performance and CODD (D: r = 0.74; P < 0.01. ND: r = 0.77; P < 0.01) and DD (D: r = 0.41, P < 0.05. ND: r = 0.44, P < 0.01). Deceleration deficit was significantly related to CODD (D: r = 0.59; P < 0.01. ND: r = 0.62; P < 0.01); however, 78% of subjects demonstrated differences between these deficit measures greater than an MWC. In conclusion, linear speed has the strongest significant relationship with 505 performance. Deceleration deficit could provide a more isolated construct than CODD which may be related to an athlete's deceleration capabilities.

Commonly used clinical criteria following ACL reconstruction including time from surgery and isokinetic limb symmetry thresholds are not associated with between-limb loading deficits during running.

OBJECTIVES: We included objective measures of gait and functional assessments to examine their associations in athletes who had recently commenced running after ACL reconstruction. DESIGN: Cross-sectional. SETTING: Sports medicine. PARTICIPANTS: 65 male athletes with a history of ACL reconstruction. MAIN OUTCOME MEASURES: Time from surgery, isokinetic knee extension/flexion strength (60°/s), and peak vertical ground reaction force (pVGRF) measured during running using an instrumented treadmill. We also investigated if a range of recommended isokinetic thresholds (e.g. > 70% quadriceps limb symmetry index) affected the magnitude of pVGRF asymmetry during running. RESULTS: There were significant relationships between quadriceps (r = 0.50) and hamstrings (r = 0.46) peak torque and pVGRF. Quadriceps peak torque explained a quarter of the variance in pVGRF (R2 = 0.24; p < 0.001). There was no association was between running pVGRF and time from surgery. Between-group differences in running pVGRF LSI% were trivial (d < 0.20) for all quadriceps and hamstring peak torque LSI thresholds. CONCLUSIONS: Current clinical criteria including time from surgery and isokinetic strength limb symmetry thresholds were not associated with lower pVGRF asymmetry measured during running. Quadriceps strength is important, but 'minimum symmetry thresholds' should be used with caution.

The Influence of Biological Maturity on Sprint Speed, Standing Long Jump, and Vaulting Performance in Young Female Gymnasts.

PURPOSE: To quantify speed, peak momentum, standing long jump (SLJ), and the ratio of vertical to horizontal take-off velocity (Ratiovert-hori TOV) in young female gymnasts of different maturity status and their influence on vaulting vertical TOV. METHODS: One hundred twenty gymnasts age 5-14 years were subdivided into maturity groupings using percentage of predicted adult height. Participants performed three 20-m sprints, SLJ, and straight jump vaults that were recorded using 2-dimensional video and analyzed using digitizing software. RESULTS: All speed intervals, peak speed, peak momentum, SLJ distance, vault height, and vertical TOV increased between the early prepubertal and late prepubertal (P < .001; d = 0.65-1.10) and early prepubertal and pubertal (P < .001; d = 0.75-1.00) groups. No differences between these metrics were observed between the 2 most mature groups (d = 0.01-0.55). Multiple regression analyses revealed peak speed had the strongest association with vertical TOV (R2 = 59%) and also identified the Ratiovert-hori as a secondary determinant (R2 = 12%). A separate regression model indicated that maturity status (percentage of predicted adult height) moderately influences vertical TOV during vaulting (R2 = 41%). CONCLUSION: Speed and SLJ performance increase between the early prepubertal and late prepubertal years in young female gymnasts. However, given that peak speed and Ratiovert-hori combined to explain 71% of the total variance in vaulting vertical TOV, in order to increase aerial time for more advanced vaulting, practitioners should attempt to enhance peak speed alongside takeoff technique to develop gymnasts' ability to transfer linear speed to vertical TOV.

Asymmetry Thresholds for Common Screening Tests and Their Effects on Jump Performance in Professional Soccer Players.

CONTEXT: Arbitrary asymmetry thresholds are regularly used in professional soccer athletes, notwithstanding the sparse literature available to examine their prevalence. OBJECTIVE: To establish normative and positional asymmetry values for commonly used screening tests and investigate their relationships with jumping performance. DESIGN: Cross-sectional study. SETTING: Elite soccer screening. PATIENTS OR OTHER PARTICIPANTS: A total of 203 professional male soccer players. MAIN OUTCOME MEASURE(S): Bilateral and unilateral jumping; range of motion; and hamstrings (HAM), quadriceps (QUAD), and hip-adductor and -abductor strength tests were used to quantify asymmetry. Players were divided into 4 quartiles (Q1-Q4) based on the magnitude of their asymmetry for each test. Single composite scores were also developed to group tests by range of motion and HAM, QUAD, hip-adduction, and hip-abduction strength, and differences in jump performance were examined among players in each quartile. RESULTS: Large variability (range = 5.2%-14.5%) was evident in asymmetry scores across the different tests and physical qualities. Forwards displayed greater asymmetry in concentric quadriceps and eccentric hip-abduction strength (P < .05). The HAM and QUAD composite scores indicated that Q4 players' jumps were shorter than those in other quartiles during a single-legged countermovement jump and 10-second hop (P < .05). No decrements in unilateral jump performance were shown among players in each quartile for range of motion or hip-adduction and -abduction strength, and no composite measures of asymmetry affected bilateral jump performance. CONCLUSIONS: No single asymmetry threshold was present for all tests; the outcomes were task, variable, and population specific. Larger asymmetries in HAM and QUAD strength appeared to be detrimental to unilateral jump performance.

The 6-m Timed Hop Is Not a Suitable Clinical Assessment Tool for Use Following Anterior Cruciate Ligament Reconstruction.

CONTEXT: Single-leg hop tests are used to assess functional performance following anterior cruciate ligament (ACL) reconstruction. Recording 6-m timed hop scores using a stopwatch increases the potential for misclassification of patient status due to the number of error sources present. OBJECTIVE: To examine the consistency of pass/fail (>90% limb symmetry index [LSI]) decisions in athletes tested at discharge following ACL reconstruction during the 6-m timed hop and the agreement between different human raters using a stopwatch and an electronic timing system. SETTING: Clinic, rehabilitation. PARTICIPANTS: A total of 20 professional soccer players (age 24.6 [4.2] y; height 175.3 [10.2] cm; mass 73.6 [14.5] kg; 36 [10.5] wk following ACL reconstruction) volunteered to take part in this study. MAIN OUTCOME MEASURES: Two individual raters recorded each trial of the 6-m timed hop test on each limb with a stopwatch and an electronic timing system acted as the criterion measure. LSI scores were also computed with a pass score >90% LSI. RESULTS: No significant differences were observed between limbs for any scoring method (P > .05). Mean differences indicated the electronic timing system was slower than both human raters (P < .05). Five participants failed the test (<90% LSI) but on each occasion this was only recorded by one method of rating. Kappa statistics showed no agreement in LSI scores across all 3 methods of scoring (κ = -.13) and no agreement when comparing the light gates to individual raters and rater 1 versus 2 (κ < 0). 95% limits of agreement in LSI scores recorded values of approximately ±20%. CONCLUSIONS: The 6-m timed hop test recorded using a stopwatch is not a valid measure to make clinical decisions following ACL reconstruction. Systematic bias between methods also suggests that a stopwatch and electronic timing system cannot be used interchangeably.

Residual deficits in reactive strength indicate incomplete restoration of athletic qualities following anterior cruciate ligament reconstruction in professional soccer players.

CONTEXT: Deficits in plyometric abilities are common following anterior cruciate ligament reconstruction (ACLR). Vertical rebound tasks may provide a targeted evaluation of knee function. OBJECTIVE: Examine the utility of a vertical hop test to assess function following ACLR and establish factors associated with performance. DESIGN: Cross-sectional Setting: Rehabilitation Participants: Soccer players with a history of ACLR (N = 73) and matched controls (N = 195) Main outcome measures: 10 second vertical hop test including measures of jump height, reactive strength index (RSI) and asymmetry. We also examined possible predictors of hop performance including single leg vertical drop jump (SLDVJ), isokinetic knee extension strength, and the international knee documentation committee questionnaire. RESULTS: Significant between-limb differences were identified for the ACLR group only and asymmetry scores increased in those with a history of ACLR (P < 0.001) compared to controls. SLDVJ RSI and knee extension torque were significant predictors of 10 second hop height (R2 = 20.1%) and RSI (R2 = 47.1%). CONCLUSIONS: Vertical hop deficits are present following ACLR even after completing a comprehensive rehabilitation program. This may be due to reduced knee extension and reactive strength. Vertical hop tests warrant inclusion as part of return to sport test battery.

Individual hop analysis and reactive strength ratios provide better discrimination of ACL reconstructed limb deficits than triple hop for distance scores in athletes returning to sport.

BACKGROUND: The triple hop for distance test commonly uses a limb symmetry index (LSI) 'pass' threshold of >90% for total hop distance following anterior cruciate ligament reconstruction (ACLR). However, understanding the manner in which athletes generate and dissipate forces during consecutive hops within the test may provide greater insight into residual limb deficits. The aim of the study was to examine reactive strength ratios (RSR) of individual hops during a triple hop test in a cohort of ACLR patients at discharge prior to return-to-sport. METHODS: Twenty male athletes (24.6 ± 4.2 years; height 175.3 ± 10.2 cm; mass 73.6 ± 14.5 kg) completed the test on both non-operated and operated limbs. Total distance hopped, contact times, flight times and RSR were collected for each hop using a floor-level optical measurement system. RESULTS: Significant, small to moderate between-limb differences (p < 0.05; d = 0.45-0.72) were shown for triple hop distance, flight time and RSR for each hop, with lower performance consistently displayed in the operated limb. Large, significant differences in RSR were evident between hops one and two on the operated limb (p < 0.05; d = 0.97). Despite 80% of participants achieving >90% LSI for total hop distance, less than 50% of participants reached the >90% LSI threshold for RSR. CONCLUSIONS: Standardised LSI 'pass' thresholds (>90% LSI) for triple hop distance may mask residual deficits in reactive strength performance of operated limbs; therefore, more detailed analyses of individual hop performance may be warranted to enhance return to sport criteria following ACLR.

Utility of the anterior reach Y-BALANCE test as an injury risk screening tool in elite male youth soccer players.

OBJECTIVES: Examine growth and maturation trends in dynamic balance using the anterior reach Y-Balance test, and its utility as an injury risk screening tool. DESIGN: Cross sectional and prospective cohort. SETTING: Elite male youth soccer players. PARTICIPANTS: 346 players grouped as pre, circa or post peak height velocity (PHV). MAIN OUTCOME MEASURES: Pre-season anterior reach absolute and relative Y-Balance test scores and seasonal prospective lower extremity injury monitoring. RESULTS: Absolute reach distances were greatest post-PHV (p < 0.05). Relative to leg length, pre-PHV achieved the highest scores and increased between-limb differences. Significant associations between injury and anterior reach scores were present in pre (OR: 0.94, CI: 0.91-0.98, p < 0.05) and circa-PHV (OR: 1.05, 95% CI: 1.05-1.10, p < 0.05). Increased age (OR: 1.49, 95% CI: 1.04-2.13, p < 0.05) and height (OR: 1.06, 95% CI: 0.99-1.13, p = 0.82) were risk factors post-PHV. No differences in injury occurrence were shown between players with absolute reach difference >4 cm in any group. CONCLUSIONS: Anterior reach scores increased injury risk, but associations were small and inconsistent. The Y-Balance should be used with caution as a screening tool in this cohort.

Using machine learning to improve our understanding of injury risk and prediction in elite male youth football players.

OBJECTIVES: The purpose of this study was to examine whether the use of machine learning improved the ability of a neuromuscular screen to identify injury risk factors in elite male youth football players. DESIGN: Prospective cohort study. METHODS: 355 elite youth football players aged 10-18 years old completed a prospective pre-season neuromuscular screen that included anthropometric measures of size, as well as single leg countermovement jump (SLCMJ), single leg hop for distance (SLHD), 75% hop distance and stick (75%Hop), Y-balance anterior reach and tuck jump assessment. Injury incidence was monitored over one competitive season. Risk profiling was assessed using traditional regression analyses and compared to supervised machine learning algorithms constructed using decision trees. RESULTS: Using continuous data, multivariate logistic analysis identified SLCMJ asymmetry as the sole significant predictor of injury (OR 0.94, 0.92-0.97, p<0.001), with a specificity of 97.7% and sensitivity of 15.2% giving an AUC of 0.661. The best performing decision tree model provided a specificity of 74.2% and sensitivity of 55.6% with an AUC of 0.663. All variables contributed to the final machine model, with asymmetry in the SLCMJ, 75%Hop and Y-balance, plus tuck jump knee valgus and anthropometrics being the most frequent contributors. CONCLUSIONS: Although both statistical methods reported similar accuracy, logistic regression provided very low sensitivity and only identified a single neuromuscular injury risk factor. The machine learning model provided much improved sensitivity to predict injury and identified interactions of asymmetry, knee valgus angle and body size as contributing factors to an injurious profile in youth football players.

The Influence of Biological Maturity and Competitive Level on Isometric Force-Time Curve Variables and Vaulting Performance in Young Female Gymnasts.

Moeskops, S, Oliver, JL, Read, PJ, Cronin, JB, Myer, GD, Haff, GG, and Lloyd, RS. The influence of biological maturity and competitive level on isometric force-time curve variables and vaulting performance in young female gymnasts. J Strength Cond Res 34(8): 2136-2145, 2020-This cross-sectional study investigated isometric force-time curve variables and vaulting performance in young female gymnasts of varying maturity and competitive levels. One hundred twenty gymnasts aged 5-14 years were subdivided into maturity groupings and also according to their competitive level. Subjects performed isometric midthigh pulls (IMTP) before completing straight jump vaults that were recorded using two-dimensional video. All significance values were accepted at p < 0.05. Absolute peak force (PF abs) and force at various time epochs were significantly greater in more mature gymnasts, although no significant differences were observed in relative peak force (PF rel). When grouped by competitive level, elite gymnasts produced a significantly greater absolute rate of force development (RFD abs) at 0-150, 0-200, and 0-250 ms as well as relative RFD (RFD rel) at 0-200 and 0-250 ms than recreational gymnasts. Based upon regression analyses, force at 50 ms during the IMTP test explained 15% of vertical takeoff velocity during vaulting. Biological maturation seems to impact isometric force-time curve characteristics in young female gymnasts, and higher-level gymnasts produce greater RFD than those competing at a lower level. Vaulting vertical takeoff velocity seems to be largely independent of isometric force-time characteristics with only a small amount of variance explained by force at 50 ms.

Lower Limb Kinetic Asymmetries in Professional Soccer Players With and Without Anterior Cruciate Ligament Reconstruction: Nine Months Is Not Enough Time to Restore "Functional" Symmetry or Return to Performance.

BACKGROUND: Residual between-limb deficits are a possible contributing factor to poor outcomes in athletic populations after anterior cruciate ligament reconstruction (ACLR). Comprehensive appraisals of movement strategies utilized by athletes at key clinical milestones during rehabilitation are warranted. PURPOSE: To examine kinetic parameters recorded during a countermovement jump with a force platform in healthy professional soccer players and to compare their performance with those who had undergone ACLR at different stages of their rehabilitation. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A total of 370 male professional soccer players attended a physical screening assessment where they performed at counter jump movement protocol on dual force plates and were divided into 4 groups: group 1 (<6 months post-ACLR), group 2 (6-9 months post-ACLR), group 3 (>9 months post-ACLR), and group 4 (healthy matched controls). RESULTS: Players in the later phases of rehabilitation increased their jump performance; however, values were significantly lower than those of healthy matched controls (P > .05). Significant between-limb differences were present for both eccentric- and concentric-phase variables (P < .05), with effect sizes ranging from moderate to very large (d = 0.42-1.35). Asymmetries were lower in players who were further away from surgery; however, between-limb differences remained significantly greater in players >9 months after ACLR versus matched controls-specifically, for concentric impulse, concentric peak force, eccentric deceleration impulse, and eccentric deceleration rate of force development asymmetry (P < .05). Logistic regression identified concentric impulse asymmetry as being most strongly associated with a history of ACLR when group prediction analysis was performed (ACLR group 1, 2, or 3 vs matched controls), with odds ratios ranging from 1.50 to 1.91. CONCLUSION: Between-limb deficits in key eccentric and concentric loading parameters remain >9 months after ACLR, indicating a compensatory offloading strategy to protect the involved limb during an athletic performance task. Concentric impulse asymmetry could be considered an important variable to monitor during rehabilitation.