Time-localized neuromuscular organization during left- and right-leg Taijiquan unilateral push-off

Unilateral lower-limb heel-kick performance requires coordinated regulation of postural control, weight transfer, and limb movement, but whether muscle-coordination patterns are organized similarly between limbs remains unclear. This study examined condition-dependent and time-localized neuromuscular organization during the Chen-style Taijiquan Deng Yi Gen task. Fifteen male elite Taijiquan athletes performed left- and right-leg heel-kick trials while bilateral surface electromyography from 12 lower-limb muscles, three-dimensional kinematics, and ground reaction forces were recorded synchronously. Muscle synergies were extracted using non-negative matrix factorization. Group-level muscle-weight patterns were identified using data-informed clustering, temporal characteristics were quantified using the center of activation and full width at half maximum, and differences in matched activation waveforms were examined using one-dimensional statistical parametric mapping. Exploratory ridge-regularized canonical correlation analysis with lag scanning was used to examine potential temporal associations between synergy activations and mechanical variables. Two recurrent group-level patterns were retained for the left-leg heel-kick condition and three for the right-leg condition. Two patterns were matched between conditions, whereas one additional unmatched group-level pattern was identified in the right-leg condition. Matched patterns showed time-localized activation differences during the later portion of the normalized movement cycle. The right-leg condition generally showed later and more temporally concentrated activation, whereas the left-leg condition showed broader activation. Exploratory rCCA identified a statistically supported temporal association only in the left-leg condition. These findings indicate condition-related differences in group-level muscle-coordination patterns and activation timing, but do not establish fixed limb-specific control or a strict stability-propulsion division.