Temporal complementarity in lower-limb neuromuscular control and kinetic asymmetries: implications for elite...

This study applied statistical parametric mapping (SPM) to examine temporal differences in bilateral lower limb neuromuscular control and kinetics during unilateral countermovement jumps (CMJ) in speed climbers, and to explore their relationship with sport-specific performance.

Fourteen elite male climbers completed unilateral CMJs and a standard 15 m speed climb. Surface electromyography and vertical ground reaction force (vGRF) were synchronously recorded. Root mean square amplitudes, knee/ankle co-contraction indices (CCI), and time-varying vGRF curves were computed, alongside asymmetry indices. SPM assessed bilateral temporal differences across the CMJ cycle, while Pearson correlation evaluated links between asymmetry and climbing time.

SPM results showed significantly higher activation of rectus femoris, biceps femoris, and tibialis anterior, as well as greater knee and ankle CCI in the left limb at specific phases (p < 0.05). vGRF exhibited phase-dependent asymmetry: the left leg produced greater force during rapid loading (30-32%), whereas the right leg showed higher output during the peak phase (90-94%). Climbing time was positively correlated with vGRF asymmetry (r = 0.61, p = 0.028), but not with CCI asymmetry (p > 0.05).

Results indicate clear functional differentiation. The left limb showed higher activation and co-contraction during braking, propulsion, and peak phases, primarily for stabilization. The right limb generated higher force during propulsion and peak phases, serving an explosive role. Notably, only vGRF asymmetry, and not neuromuscular asymmetry, was associated with performance. These findings suggest that training may prioritize balancing macroscopic kinetic output (i.e., reducing vGRF asymmetry) rather than pursuing inter-limb neuromuscular symmetry.