A EFFECT OF ECCENTRIC HAMSTRING STRENGTHENING ON JUMP PERFORMANCE IN YOUNG MALE FOOTBALL PLAYERS WITH GRADE 1 ACL INJURIES: A RANDOMIZED CONTROLLED TRIAL

Abstract

Background: Anterior cruciate ligament (ACL) injuries compromise lower-limb power, neuromuscular control, and explosive functional performance, all of which are critical for return-to-sport in competitive footballers. Jump performance, commonly assessed via vertical jump testing, reflects the combined contribution of quadriceps and hamstring strength and is a widely used proxy for functional readiness after knee injury. Although eccentric hamstring training is increasingly incorporated into ACL rehabilitation for its role in enhancing neuromuscular control and hamstring strength, its specific effect on jump performance in athletes with Grade 1 (mild) ACL injuries has not been well characterized. Objective: To evaluate the effect of adding eccentric hamstring strengthening to conventional physiotherapy on vertical jump performance in young male football players with non-contact Grade 1 ACL injuries. Methods: This was a preregistered secondary outcome analysis from a randomized, open-label, two-arm parallel-group trial conducted at football clubs across the UAE. A total of 180 male football players aged 18– 25 years with an acute (within 6 weeks), physician-diagnosed, non-contact Grade 1 ACL injury were randomized 1:1 to conventional physiotherapy alone (Control, n=90) or conventional physiotherapy combined with progressive eccentric hamstring exercises (Experimental, n=90). Both programs were delivered 5 days/week for 12 weeks under physiotherapist supervision. Jump performance was assessed using the Sargent vertical jump test at baseline and at 12 weeks. Between- and within-group differences over time were analyzed using a two-way mixed-design ANOVA (group × time), with partial eta-squared (η²p) reported as the effect size measure. Results: Baseline jump height did not differ significantly between groups. Both groups showed significant improvement in jump height from baseline to 12 weeks (Control: 58.2 ± [4.5] cm to 65.3 ± [4.8] cm; Experimental: 57.9 ± [4.5] cm to 68.3 ± [4.2] cm; main effect of time, F(1,178)=2714.80, P<.001, η²p=.938). A significant group × time interaction indicated a significantly greater improvement in the experimental group compared with the control group (F (1,178) =95.92, P<.001, η²p=.350). The main effect of group (collapsed across time) was not statistically significant (F (1,178) =0.95, P=.331), consistent with comparable baseline jump performance between groups. Conclusion: Both conventional physiotherapies alone and physiotherapy combined with eccentric hamstring training improved jump performance over 12 weeks; however, the addition of eccentric hamstring training was associated with significantly greater improvement. These findings support eccentric hamstring strengthening as a beneficial adjunct to conventional physiotherapy for optimizing functional recovery of lower-limb power in young footballers with Grade 1 ACL injuries. Keywords: ACL rehabilitation; eccentric training; jump performance; Sargent vertical jump test; football players; randomized controlled trial.