The Timing of Thigh Muscle Activity Is a Factor Limiting Performance in the Deceleration Phase of the 100-m Dash

Purpose We aimed to examine the timing of electromyography activity of the rectus femoris (RF) and biceps femoris (BF) in both legs, as well as spatiotemporal variables (running speed (RS), step frequency (SF), step length (SL)) between the maximal speed (Max) phase (50-70 m) and the deceleration (Dec) phase (80-100 m) of the 100-m dash. Methods Nine track and field athletes performed the 100-m dash with maximal effort. Spatiotemporal variables of each 10-m section were measured. A portable wireless data logger was attached to the subject's lower back to record electromyographies. We calculated onset/offset timing (%) of RF and BF in both legs using a Teager-Kaiser Energy Operator filter (e.g., ipsilateral leg RF onset is iRF-onset, contralateral leg BF onset is cBF-onset) in a running cycle. Results The decreased RS in the Dec phase (P < 0.001) was due to a decreased SF (P < 0.001). Moreover, iRF-onset (P = 0.002), iRF-offset (P = 0.008), iBF-offset (P = 0.049), and cBF-offset (P = 0.017) in the Dec phase lagged in the running cycle as compared with the Max phase. Furthermore, the time difference between the swing leg RF activity (iRF-onset) and the contact leg BF activity (cBF-onset; Scissors1) became bigger in the Dec phase (P = 0.041). Significant negative correlations were found between Delta iRF-onset and Delta SF (P = 0.045), and between Delta iBF-offset and Delta SF (P = 0.036). Conclusions The decreased RS and SF in the Dec phase of the 100-m dash would be the delayed timing of the RF and BF activities in the same leg as well as the disturbed interleg muscular coordination.

Automated summary

This study aimed to examine the timing of electromyography activity and spatiotemporal variables in the different phases of the 100-m dash. The results showed that in the deceleration phase, running speed and step frequency decreased, and the timing of the rectus femoris and biceps femoris activities lagged compared to the maximal speed phase. Additionally, the time difference between the swing leg and contact leg muscle activities increased in the deceleration phase.