Selective differences in eccentric inter-limb mechanics during single-leg vertical jump six months after anterior cruciate ligament reconstruction.

OBJECTIVES: To investigate inter-limb eccentric mechanical characteristics during the single-leg countermovement jump (SLCMJ) six months after anterior cruciate ligament reconstruction (ACLR), and secondarily to explore multidimensional patterns across eccentric variables. DESIGN: Prospective observational study. SETTING: Laboratory-based biomechanical assessment using force platforms. PARTICIPANTS: Forty-four male participants (22 ACLR at 6 months after ACLR, 22 matched controls). MAIN OUTCOME MEASURES: Peak eccentric force, eccentric impulse, center of mass displacement, and eccentric velocity during the eccentric phase. Variables were standardised using control-referenced z-scores. Inter-limb differences were analysed using linear mixed-effects models. Principal component analysis (PCA) and exploratory k-means clustering examined multidimensional patterns, with k-selection and control-group sensitivity analyses. RESULTS: A group × limb interaction was found for peak eccentric force (β = 0.354, 95% CI 0.049 to 0.658; p = 0.023), although the Holm-adjusted sensitivity p value was 0.092; no interaction was observed for impulse (p = 0.858), displacement (p = 0.605), or velocity (p = 0.546). PCA identified two components explaining 87.2% of variance (PC1: 59.6%, PC2: 27.6%). The forced k = 2 ACLR partition comprised 11 and 11 participants (silhouette = 0.39), but the gap statistic favoured k = 1; comparable forced partitions were also observed in control limbs. CONCLUSIONS: Peak eccentric force showed a selective group × limb interaction, but this finding was sensitive to multiplicity and to the non-equivalent limb axes used across groups. Multidimensional patterns were also present in controls and should be considered exploratory rather than ACLR-specific.