Evaluating kinetic symmetry during loaded and unloaded jumping across multiple rehabilitation phases in ACLR patients

BACKGROUND: The rehabilitation of patients following anterior cruciate ligament reconstruction (ACLR) requires objective assessments that can identify between-limb asymmetries in jump performance to guide return-to-play (RTP) decisions. This study investigated kinetic asymmetries in ACLR patients using loaded and unloaded vertical jumping across multiple rehabilitation phases to assess neuromuscular recovery and readiness for RTP. METHODS: Participants (ACLR, n = 18; 14 males and 4 females; ages 20 ± 2.46 years) completed unilateral countermovement jumps (CMJUL), unilateral drop jumps (DJUL), and loaded squat jumps (SJ) on dual force plates during phases 3 (~ 16 weeks), and 4 (~ 20 weeks) of rehabilitation. Metrics including reactive strength index (RSI), jump height (JH), and force-velocity (FV) profiles analysed for inter-limb asymmetries. Statistical analyses included statistical parametric mapping to evaluate between-limb differences in the force-time waveforms and repeated measures ANOVAs for jumping-based metrics with standardised effect sizes (Cohen’s d) calculated for key pairwise comparisons of the between-limb differences. RESULTS: Significant between-limb asymmetries were observed throughout key phases of the force-time waveform in both CMJUL and DJUL tests (p < 0.001), with moderate-to-large effect sizes for RSI (d = 1.32–1.41) and JH (d = 1.53–2.01) across both phases. Force asymmetries persisted in the propulsive phases of CMJUL and DJUL and loaded SJ trials revealed substantial force production asymmetries (mean asymmetry angle > 25%, p < 0.001) at higher velocities. Correlation analyses showed strong associations between RSI and JH in CMJUL and DJUL (r = 0.70–0.89). CONCLUSIONS: Jump analyses provide valuable insights regarding neuromuscular recovery in ACLR patients, revealing significant and persistent asymmetries through late rehabilitation phases. These findings highlight the importance of phase-specific, targeted interventions to address neuromuscular deficits and support safe RTP decisions.