Decoupling of kinetic and kinematic asymmetry in elite sculling: catch slip synchronization is more closely associated with boat speed than force balance

BACKGROUND: To investigate the phase-dependent behavior of kinematic and kinetic asymmetry during an on-water incremental 2000-m test and to determine which asymmetry components were independently associated with boat speed in elite scullers. METHODS: Twelve elite male single scullers completed a continuous 2000 m on-water incremental test. Multiple strokes were recorded in each of seven analyzed stroke-rate phases; left and right variables were averaged within each rower × phase block and converted to asymmetry indices (AI), yielding 84 phase-level observations. Phase effects were evaluated with one-way repeated-measures ANOVA, latent structure with principal component analysis (PCA), exploratory bivariate associations with Spearman's rho, and independent correlates of speed with a linear mixed-effects model (LMM) including a random intercept for subject. RESULTS: Kinetic asymmetry exhibited large phase effects: Work per Stroke AI and Drive-angle span > 70% Peak Force AI increased from SR 20 to SR 39 (both p < 0.001; ηp² ≥ 0.80) before decreasing in the final sprint. Power per Stroke AI was not entered as an independent asymmetry variable because it was algebraically equivalent to Work per Stroke AI at the phase level. By contrast, macro-kinematic asymmetry remained low overall. Slip variables were numerically much larger and more variable than the macro-kinematic AIs. PCA identified a dominant kinetic/intensity dimension and separate slip-related dimensions. In the LMM (marginal R² = 0.36), Catch Slip AI was the only significant fixed effect associated with boat speed (β = -0.314, p = 0.018), whereas Work per Stroke AI was not (β = 0.236, p = 0.106). CONCLUSIONS: In elite sculling, force-related asymmetry appears to behave mainly as an intensity-linked correlate rather than an independent limiter of speed. In contrast, poorer bilateral synchronization of catch slip is associated with lower boat speed, suggesting that catch timing may represent a more relevant technical target than absolute force balance. TRIAL REGISTRATION: Chinese Clinical Trial Registry (ChiCTR2500112689), registered on 18 November 2025.