Unilateral Numbers Need Context: Reference Values for Single-Leg CMJ Performance Relative to Bilateral CMJ Capacity

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Abstract
The single-leg countermovement jump (SL CMJ) is widely used to assess limb-specific neuromuscular function, with interpretation commonly centred on inter-limb asymmetry. However, contextualising unilateral performance relative to bilateral capacity remains less clearly defined. This retrospective cross-sectional study aimed to develop exploratory descriptive benchmarks for SL CMJ kinetic, kinematic, and temporal variables expressed as a percentage of bilateral CMJ performance in a heterogeneous athletic cohort. A total of 348 athletes completed bilateral and unilateral CMJs using dual force plate sampling at 1000 Hz. The best trials were selected using the modified reactive strength index (mRSI), and averaged unilateral variables were expressed relative to bilateral potential. Unilateral-to-bilateral transfer was non-uniform across metric domains. Median relative jump height and the mRSI were 44.8% and 39.4%, respectively, whereas median average relative braking and propulsive force values were 76.0% and 75.4%, respectively. Gross impulse measures were retained to a greater extent than power- and rate-dependent variables, while temporal metrics showed prolonged unilateral phase durations. Exploratory sex-based analyses indicated trivial-to-small differences in selected variables; however, these findings should be interpreted cautiously because of unequal group sizes and the descriptive nature of the dataset. These results provide broad exploratory percentile benchmarks that may help practitioners contextualise SL CMJ performance relative to bilateral execution. However, the values should not be interpreted as universal clinical thresholds, injury-risk markers, or sport-specific normative standards without consideration of sex, sport discipline, competitive level, injury history, and longitudinal athlete context.

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