Biomechanical analysis of the flutter kick in diving: kinematics, muscle activation and coordination of lower limbs

This study aims to investigate the biomechanics of the flutter kick in diving, including lower limb kinematics, muscle activation patterns, and coordination, as well as how these characteristics change under varying diving speeds. Ten divers performed 100-meter underwater swimming at self-selected normal and fast speeds, and their lower limb kinematic data and surface electromyography signals from eight muscles were collected. Based on the refined phase division of the kicking cycle into two transition phases, a power phase, and a recovery phase, the movement pattern featuring bending waves is characterized by hip-driven sequential activation of the knee and ankle joints. The quadriceps serve as the primary power source, while the shank muscles provide joint stabilization. Muscle activation analysis revealed two synergistic patterns, with the tibialis anterior and gastrocnemius lateralis exhibiting activation in both patterns and showing the highest co-activation index. With increasing speed, the peak angular velocities of all joints increased. The range of motion of the ankle joint increased, while the timing of its peak angular velocity was later. Although the muscle activation patterns remained similar, they exhibited a prolonged duration and increased amplitude of activation. This study enhances the understanding of the flutter kick with fins in diving.