Explosive Hamstrings Strength Asymmetry Persists Despite Maximal Hamstring Strength Recovery Following Anterior Cruciate Ligament Reconstruction Using Hamstring Tendon Autografts

PURPOSE: To investigate the differences in maximal (isometric and concentric peak torque) and explosive (rate of torque development (RTD)) hamstring and quadriceps strength symmetry between males and females during early- and late-phase rehabilitation after anterior cruciate ligament reconstruction (ACLR) using hamstring tendon (HT) autografts and to determine the interaction of time and sex on maximal and explosive strength symmetry. METHODS: A total of 38 female and 51 male participants were assessed during early (3–6 months post-operative) and late (7–12 months post-operative) phases of rehabilitation following ACLR. Maximal (concentric and isometric peak torque) and explosive (isometric RTD) hamstring and quadriceps strength were assessed and presented as limb symmetry index (LSI). RESULTS: Maximal concentric hamstrings asymmetry (Early: 86 ± 14; Late 92 ± 13; p = 0.005) as well as maximal concentric (Early, 73 ± 15; Late 91 ± 12; p < 0.001) and explosive (Early: 82 ± 30; Late: 92 ± 25; p = 0.03) quadriceps asymmetry decreased from early to late rehabilitation. However, there were no significant changes in maximal isometric quadriceps strength and explosive isometric hamstring strength in the same time period. Females had a larger asymmetry in maximal concentric (Females: 75 ± 17; Males: 81 ± 15; p = 0.001) and explosive (Females: 81 ± 32; Males: 89 ± 25; p = 0.01) quadriceps strength than males throughout rehabilitation. There were no sex differences in maximal and explosive hamstring strength. There were no sex by time interactions for any variables. CONCLUSION: Explosive hamstring strength asymmetry did not improve despite recovery of maximal hamstring strength during rehabilitation following ACLR with HT autografts. While sex did not influence strength recovery, females had larger maximal and explosive quadriceps strength asymmetry compared to males throughout rehabilitation following ACLR. LEVEL OF EVIDENCE: Level III SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00167-022-07096-y

Strength and biomechanical risk factors for noncontact ACL injury in elite female footballers : A prospective study

Purpose This study aimed to determine if a preseason field-based test battery was prospectively associated with noncontact anterior cruciate ligament (ACL) injury in elite female footballers. Methods In total, 322 elite senior and junior female Australian Rules Football and soccer players had their isometric hip adductor and abductor strength, eccentric knee flexor strength, countermovement jump (CMJ) kinetics, and single-leg hop kinematics assessed during the 2019 preseason. Demographic and injury history details were also collected. Footballers were subsequently followed for 18 months for ACL injury. Results Fifteen noncontact ACL injuries occurred during the follow-up period. Prior ACL injury (odds ratio [OR], 9.68; 95% confidence interval (95% CI), 2.67–31.46), a lower isometric hip adductor to abductor strength ratio (OR, 1.98; 95% CI, 1.09–3.61), greater CMJ peak take-off force (OR, 1.74; 95% CI, 1.09–3.61), and greater single-leg triple vertical hop average dynamic knee valgus (OR, 1.97; 95% CI, 1.06–3.63) and ipsilateral trunk flexion (OR, 1.60; 95% CI, 1.01–2.55) were independently associated with an increased risk of subsequent ACL injury. A multivariable prediction model consisting of CMJ peak take-off force, dynamic knee valgus, and ACL injury history that was internally validated classified ACL injured from uninjured footballers with 78% total accuracy. Between-leg asymmetry in lower limb strength and CMJ kinetics were not associated with subsequent ACL injury risk. Conclusions Preseason field-based measures of lower limb muscle strength and biomechanics were associated with future noncontact ACL injury in elite female footballers. These risk factors can be used to guide ACL injury screening practices and inform the design of targeted injury prevention training in elite female footballers