Timing of Rectus Femoris and Biceps Femoris Muscle Activities in Both Legs at Maximal Running Speed

Purpose The purpose of this study was to investigate the relationship between spatiotemporal variables of running and onset/offset timing of rectus femoris (RF) and biceps femoris (BF) muscle activities in both legs. Methods Eighteen male well-trained athletes (age = 20.7 +/- 1.8 yr) were asked to run 50 m at maximal speed. The spatiotemporal variables (running speed, step frequency, and step length) over the distance from 30 to 50 m were measured. In addition, RF and BF muscle activities were obtained from both legs using wireless EMG sensors. To quantify the onset and offset timing of muscle activity, the band-pass filtered (20-450 Hz) EMG signal was processed using a Teager-Kaiser energy operator filter. We calculated RF and BF onset/offset timings (%) in both legs (e.g., ipsilateral leg RF [iRF] and contralateral leg BF [cBF]) during running cycle. Based on those timings, we obtained the EMG timing variables (%) as follows: Switch1 (iBF-offset to iRF-onset), Switch2 (iRF-offset to iBF-onset), Scissors1 (cBF-onset to iRF-onset), and Scissors2 (iRF-offset to cBF-offset). Results We found that Switch2 had positive (r = 0.495, P = 0.037), Scissors1 had negative (r = -0.469, P = 0.049), and Scissors2 had positive (r = 0.574, P = 0.013) correlations with step frequency. However, these variables had no significant correlations with running speed or step length. Conclusions These results indicate that higher step frequency would be achieved by smoother switching of the agonist-antagonist muscle activities and earlier iRF activation relative to the cBF activity. To improve sprint performance, athletes and coaches should consider not only muscle activities in one leg but also coordination of muscle activities in both legs.

Automated summary

The study found that higher step frequency is correlated with smoother switching of agonist-antagonist muscle activities and earlier activation of the rectus femoris relative to the biceps femoris. To improve sprint performance, athletes and coaches should consider coordination of muscle activities in both legs, not just focusing on muscle activities in one leg.