Understanding lower-limb synergies and their role in angular momentum transfer: A biomechanical analysis on tennis double-handed backhand

Effective force transmission in the closed-stance two-handed backhand stroke depends on coordinated lower-limb movement. This study investigated the temporal characteristics of lower-limb synergies and their relationship with angular momentum transfer in the supporting leg. Sixteen elite and fourteen sub-elite tennis players performed backhand strokes captured via synchronized force platforms and motion capture. Singular value decomposition (SVD) was used to extract synergy patterns, and cross-correlation functions (CCF) assessed the temporal relationship between synergy activation and angular momentum across foot, shank, thigh, and pelvis segments. Three consistent synergies were identified in both groups. However, elite players displayed better synergy structures and tighter temporal synchronization ( p < 0.05). Specifically, Synergy 1 enhanced angular momentum transfer in the thigh and pelvis, Synergy 2 improved rotational control in the shank and pelvis, and Synergy 3 facilitated footwork adjustment and postural stability. These synergies showed stronger correlations and more consistent timing in elite athletes. The findings suggest that optimizing lower-limb synergy timing enhances angular momentum transfer efficiency, rotational stability, and coordination during stroke execution, offering valuable insight for performance training in tennis.