860 FO19 – Influence of velocity and resistance on lower-limb electromyographic activity during sprint running

Background Various training programs aim to make athletes faster by using methods like sprinting with additional resistance. Given that sprint running is associated with a high risk of hamstring injuries, it is of major importance for injury prevention to assess the effect of such training on lower limb electromyographic (EMG) activity. Objective To assess lower limb EMG activity in response to running velocity and resistance. Design Cross-sectional study. Setting One-time measurement in elite athletes who competed in Olympic and World events across athletics, rugby sevens, and bobsleigh. Participants 37 elite athletes (age:27.0±3.3 years, height:173.7±10.2 cm, weight:70.9±13.2kg). Interventions They performed an unresisted condition consisting in a 40-m maximal sprint, and two resisted conditions corresponding to 25% and 75% of body mass. Main Outcome measurements EMG activity was recorded on eight muscles from the hamstring, quadriceps and gluteal muscle groups. The running cycle was divided into stance and swing phases in which average EMG activity was computed. Results Hamstring EMG activity increased with velocity (p<0.001) in stance (+20.6%) and swing (+7.7%) phases, except for semitendinosus, which decreased in swing (-4.1%, p<0.001). Differently, quadriceps showed reduced EMG activity (p<0.001) during the stance phase (-8.2%) but increased activity during the swing phase, especially for the rectus femoris (+3.4%). Hamstring EMG activity was higher (p<0.05) without resistance in stance (+16%) and swing (+3.2%) phases, while rectus femoris exhibited higher activity with increased resistance (+12% in stance phase). Conclusions The increase in hamstring EMG activity with velocity could be partly explained by the influence of the force-length relationship as the body position inclines during the acceleration phase of the sprint. Resisted sprint condition could be an appropriate method for reducing hamstring EMG activity, while increasing quadriceps activity. The muscle-specific changes as a function of velocity and resistance should be considered in injury prevention or performance optimization.