The Development of Joint Kinematics, Kinetics and Electromyography Activity over 50 m Sprints in Experienced Sprinters

Background: The aim was to investigate the stride-by-stride development of spatiotemporal parameters, joint kinematics, kinetics, and electromyographic (EMG) activity during a 50 m sprint, providing a comprehensive analysis of the biomechanical and neuromuscular changes throughout the entire sprint. Methods: Fifteen male sprinters (age 20.5 ± 1.3 years, body mass 66.8 ± 4.5 kg, body height 1.74 ± 0.06 m, 100 m personal best: 11.24 ± 0.34 s) performed a 50 m sprint, while the spatiotemporal parameters, joint kinematics, kinetics, and EMG activity of nine muscles were measured. Results: The main findings were that the 50 m sprint could be divided into three phases: initial acceleration, transition and maximal velocity and involve tightly coordinated changes across multiple biomechanical domains. The initial acceleration (the first 3–5 strides) was dominated by rapid increases in stride frequency, rapid changes in joint angles, and rising EMG activity in key muscles. In the transition phase (up to ~30–35 m), continued increases in stride length, decreasing contact time, and stabilization of kinematics and EMG activity were the main characteristics. In the maximal-velocity phase, a plateau in velocity, increased flight time, greater reliance on vertical force (an increase in vertical force relative to the horizontal forces), and stabilized neuromuscular patterns were observed. Conclusion: The phased progression supports contemporary biomechanical models of sprinting and emphasizes the importance of both mechanical and neuromuscular efficiency in achieving optimal sprint performance.