Analysis of the correlation between lower limb muscle synergy characteristics and landing load during single-leg landing in humans

To explore the correlation between the characteristics of lower limb muscle synergies and landing loads during the single-leg landing process in humans. Lower limb electromyographic data were collected from 21 male athletes during single-leg landing. The non-negative matrix factorization algorithm was used to extract analytical indicators, including the number of participating muscle synergies, the time to peak activation of muscle synergies, and the relative muscle weights. Additionally, the associations between the above indicators and the loads during human single-leg landing were analyzed. In the number of synergies, three types of muscle synergies were identified during single-leg landing. The number of synergies showed a significant negative correlation with peak landing impact force and lower limb stiffness(P < 0.05). In the time to peak activation, the synergy 1 of peak activation time was significantly positively correlated with lower limb stiffness (P < 0.05). The synergy 3 of peak activation time was significantly positively correlated with peak impact force (P < 0.05). In the muscle relative weights, the synergy 1 of the relative weight of the rectus femoris was significantly negatively correlated with peak impact force (P < 0.05), while the semitendinosus was negatively correlated with maximum loading rate (P < 0.05). The Synergy 3 of the relative weight of the tibialis anterior was significantly positively correlated with peak impact force (P < 0.05). (1) Increasing the number of participating synergies can stimulate more muscle activity, which contributes to finer coordination and distribution of the impact forces on the body during single-leg landing. (2) Faster activation of synergies governing the landing absorption phase enhances eccentric control of knee extensors, reducing lower limb stiffness. Conversely, quicker activation of synergies dominant in the initial landing impact phase improves calf muscle engagement for energy dissipation. (3) Enhancing the eccentric strength of the rectus femoris during the landing absorption phase reduces muscle stiffness, promoting knee flexion buffering. However, excessive tibialis anterior activation should be avoided to prevent premature compensatory dorsiflexion at the ankle joint.