Effect of high-intensity intermittent cycling sprints on neuromuscular activity

High-intensity intermittent sprints induce changes in metabolic and mechanical parameters. However, very few data are available about electrical manifestations of muscle fatigue following such sprints. In this study, quadriceps electromyographic (EMG) responses to repeated all-out exercise bouts of short duration were assessed from maximal voluntary isometric contractions (MVC) performed before and after sprints. Twelve men performed ten 6-s maximal cycling sprints, separated by 30-s rest. The MVC were performed pre-sprints ((pre)), post-sprints ((post)), and 5 min post-sprints ((post5)). Values of root-mean-square (RMS) and median frequency (MF) of vastus lateralis (VL) and vastus medialis (VM) were recorded during each MVC. During sprints, PPO decreased significantly in sprints 8, 9, and 10, compared to sprint 1 (-8%, -10%, and -11%, respectively, p < 0.05). Significant decrements were found in MVCpost (-13 %, p < 0.05) and MVCpost5 (-10.5%, p < 0.05) compared to MVCpre. The RMS value of VL muscle increased significantly after sprints (RMSpre vs. RMSpost: + 15%, p < 0.05). Values of MF decreased significantly in both VL and VM after sprints. In conclusion, our results indicate that the increase in quadriceps EMG amplitude following high-intensity intermittent short sprints was not sufficient to maintain the required force output. The concomitant decrease in frequency components would suggest a modification in the pattern of muscle fiber recruitment, and a decrease in conduction velocity of active fibers.