How Do Multi- and Single-Joint Strength Levels Relate to Vertical Jump Performance and Biomechanics in Amateur Athletes Returned to Sport After Anterior Cruciate Ligament Reconstruction?

ABSTRACT: Maestroni, L, Turner, A, Rosalia, A, Algeri, C, Moioli, F, Guastella, M, Civera, F, Midali, C, Bettariga, F, and Read, P. How do multi- and single-joint strength levels relate to vertical jump performance and biomechanics in amateur athletes returned to sport after anterior cruciate ligament reconstruction? J Strength Cond Res 40(1): 39-47, 2026-Understanding the relationship between multijoint and single-joint strength and vertical jumps performance, stretch-shortening cycle (SSC) function, and phase-specific impulses in athletes after anterior cruciate ligament (ACL) reconstruction is necessary to optimize rehabilitation strategies by identifying the hierarchy of physical qualities that underpin complete recovery after ACL reconstruction. Fifty-four amateur athletes completed a strength and vertical jump assessment. Relative 5RM box squat, rear-foot elevated split squat (RFESS), and leg extension explained between 25.2 and 56.9% of the variance in countermovement jump (CMJ) height, single-leg (SL) CMJ height, reactive strength index modified (RSImod), and SL drop jump (DJ) height and reactive strength index (RSI). Relative 5RM box squat and RFESS were consistent predictors. Relative 5RM RFESS and leg extension strength explained between 22.1 to 31% and 17 to 47.2% of the variance in CMJ and SLCMJ concentric and eccentric deceleration impulses, respectively. Leg extension was a significant independent predictor for most phase-specific impulse variables. The logistic regression analysis did not show any predicting ability of both 5RM RFESS and leg extension scores in identifying SSC function. A stronger association with CMJ, SLCMJ, and SLDJ performance was found for relative 5RM box squat and RFESS. 5RM leg extension was a significant predictor in explaining part of the variance in CMJ and SLCMJ concentric and eccentric deceleration impulses. Impaired SSC efficiency was present, but not predicted by strength scores. Our findings underscore the importance of both multi- and single-joint strength in explaining jump performance and phase-specific impulses, while indicating that SSC efficiency is influenced by additional neuromuscular factors beyond strength alone.