Lower limb muscle synergies during deceleration at different change of direction angles.

Change of direction is a core technical action in many competitive sports such as football and basketball, and it plays a crucial role in athletes' performance. Deceleration, which is the foundation of changing direction, has been proven to be a key element in athletes' rapid directional changes . This study collected electromyographic signals during the deceleration phase of a [Formula: see text] left change of direction in 16 male college football players, and analyzed their muscle synergies using non-negative matrix factorization to extract key indicators such as the number of synergy modules and muscle weights. The study found that two stable muscle synergy modules could be extracted during the deceleration phase of both [Formula: see text] changes of direction. synergy module 1 was dominated by the biceps femoris, semitendinosus, and vastus lateralis; synergy module 2 was dominated by the rectus femoris, vastus medialis, and tibialis anterior. When the change of direction angle increased from [Formula: see text], the weight of the tibialis anterior in synergy module 1 significantly decreased (P=0.029), and the weights of the vastus lateralis and biceps femoris in synergy module 2 significantly increased (P=0.014 and P=0.049). Other synergy parameters (such as the time to peak activation, the degree of synergy module activation, the proportion of obvious activation duration, overall activation degree, and co-activation duration) showed no significant differences ([Formula: see text]). This indicates that during deceleration in both [Formula: see text] changes of direction, there are two stable muscle synergy modules. synergy module 1 is dominated by the biceps femoris, semitendinosus, and vastus lateralis, while synergy module 2 is centered around the rectus femoris, vastus medialis, and tibialis anterior. These two elements are jointly responsible for deceleration, initial direction change, and joint stability maintenance. As the change of direction angle increases, the human lower limb prioritizes enhancing knee joint stability, at the expense of some ankle joint control. Therefore, targeted training should focus on optimizing knee joint stability, strengthening the eccentric force of the hamstring muscles, and improving dynamic control of the ankle joint.