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

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. 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. 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). 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.