Sprint gait: coactive roles of femoral biarticular muscles with femoral monoarticular and lower leg muscles

The 100-meter sprint is a central focus in sports biomechanics due to its relevance to performance enhancement. In this study, we reviewed electromyographic (EMG) data from ground sprinting and analyzed stride and joint kinematics from treadmill sprinting to examine and propose the coactive roles of femoral biarticular muscles alongside femoral monoarticular and lower leg muscles during sprint gait. The EMG data were interpreted using the static two-joint link model, which characterizes the functional coordination of human femoral muscles. According to the model, activity switches occur among three antagonistic pairs of femoral muscles at distinct phases of the sprint cycle. Concurrently, six muscle pairs generate sequential combined force outputs, applied to specific sectors of the ankle joint, contributing to coordinated movement at the hip, knee and ankle joints. During the stance phase, the coactivity of the gluteus maximus and/or biceps femoris long head facilitates hip extension and forward propulsion, while the gastrocnemius and soleus support plantar flexion and ground reaction force modulation. We conclude that femoral biarticular muscles play significant coactive roles with femoral monoarticular and lower leg muscles during sprinting. The EMG and treadmill kinematic analyses provide valuable insights into the biomechanics of sprint gait.