Author(s): KAKEHATA, G., TAKEI, N., Institution: WASEDA UNIVERSITY, Country: JAPAN, Abstract-ID: 441

INTRODUCTION:
Repeated sprint exercise (RSE), involving maximal-intensity efforts with short recovery intervals until exhaustion, is a widely used and effective training method among athletes. However, the characteristics of neuromuscular behavior involvement during RSE remain unclear. Purpose of this study was to investigate neuromuscular fatigue during RSE from the perspective of neuromuscular responses in track and field sprinters.
METHODS:
The task was repeated 30-m maximal sprint running. Nine male track and field athletes participated in this study. Each continued until their sprint time declined by 10% compared with the first trial, with 20 s of rest between runs. Surface electromyography (EMG) was recorded from eight muscles of one lower limb (gluteus maximus, rectus femoris, biceps femoris, semitendinosus, vastus lateralis, tibialis anterior, soleus, gastrocnemius lateralis). Spatiotemporal variables were measured using a high-speed camera and timing gates. The running cycle was divided into four phases (contact, early-swing, mid-swing, and late-swing), and integrated EMG (iEMG) was calculated for each four phases. Three sprints were analyzed: the first trial, the trial at 5% speed reduction, and the trial at 10% reduction.
RESULTS:
As fatigue progressed, running speed and step frequency significantly decreased. Significant interactions were observed for iEMG in the rectus femoris and gluteus maximus. In particular, rectus femoris activity decreased during early and mid-swing, while gluteus maximus activity decreased during stance, mid-swing, and late-swing phases.
CONCLUSION:
An important finding of this study was that neuromuscular activity of the hip muscles was selectively attenuated as fatigue progressed during repeated sprint exercise. These muscles play a key role in sprint acceleration by generating ground reaction force through hip extension and facilitating swing-leg recovery, and are therefore essential for achieving high running speed. The present results indicate that neuromuscular fatigue during repeated sprint exercise does not occur uniformly across all muscles, but rather selectively, reflecting muscle-specific characteristics. Despite the decline in sprint performance, several muscles maintained relatively stable activation, suggesting compensatory motor control strategies to preserve overall movement patterns under fatigued conditions. This selective fatigue behavior may be related to differences in functional roles, mechanical loading, and fatigue resistance among muscles. From a practical perspective, these findings highlight the importance of training interventions aimed at improving fatigue resistance of the hip extensors and flexors to maintain sprint performance during repeated high-intensity efforts. In conclusion, neuromuscular fatigue during repeated sprint exercise is characterized by muscle- and phase-specific alterations in activation, highlighting the importance of hip musculature in repeated sprint performance.