Measuring Changes in Hamstring Contractile Strength and Lower Body Sprinting Kinematics During A Simulated Soccer Match

Background - Hamstring strain injuries (HSI’s) in soccer occur most frequently during the latter stages of each half. Neuromuscular fatigue (NMF) may induce changes in hamstring contractile strength and sprinting technique, which are potential causes for the observed increase in HSI risk during each half.Objectives - The aim of this study was to examine the effects of soccer specific fatigue on hamstring maximal voluntary torque (MVT), hamstring rate of torque development (RTD), and alterations in sprinting technique. Moreover, the possibilities to detect alterations in sprinting technique as potential markers for increased HSI risk were explored using inertial measurement units (IMU’s).Methods - Ten amateur soccer players executed a 90-minute soccer match simulation. Before and after each 15-minute segment hamstring MVT (Nm), hamstring neuromuscular activity (%EMGmax), hamstring RTD (Nm.s), and sprint performance and technique were assessed. Sprinting kinematic data was obtained using IMU’s. Repeated measurement ANOVAS were used to assess changes in hamstring contractile properties, sprint performance, and sprinting kinematics. Repeated measurement correlation was used to assess common within subject associations between hamstring MVT, sprint performance and sprinting kinematics.Results - Significant time dependent reductions in hamstring MVT (푃 < 0.01), corresponding hamstring EMG activity (푃 < 0.01), and sprint performance (푃 < 0.01) were observed. Significant positive within subject repeated measurement correlations were observed between hamstring MVT and knee angle at peak knee extension in the final part of the swing phase (푃 < 0.05), between hamstring MVT and hip angle at peak hip flexion (푃 < 0.01), and between hamstring MVT and peak hip flexion velocity (푃 < 0.01).Conclusions - The findings of present study suggest that the capacity of the hamstrings to decelerate the lower limb in sprint running is limited during soccer-specific NMF, resulting in greater peak knee extension during the terminal swing phase. As a consequence, the risk of excessive hamstring strain, and thus HSI risk, may be elevated. Moreover, present results show that IMU’s can be used to detect NMF-induced changes in sprinting technique as potential markers for increased HSI risk.Mechanical Engineering | BioMechanical Desig