Author(s): RABITA, G., MACCHI, R., HEGYI, A., GIROUX, C., HOLLVILLE, E., COUTURIER, A., LACOURPAILLE, L., NORDEZ, A., GUILHEM, G., Institution: FRENCH INSTITUTE OF SPORTS (INSEP), Country: FRANCE, Abstract-ID: 2558

INTRODUCTION:
External resistance is widely used to manipulate running velocity and increase horizontal force production during sprint acceleration. It has been shown that both external resistance and speed influence hamstring and quadriceps activity (1). On the other hand, when comparisons are performed under velocity-matched conditions, only minor kinetic and kinematic differences are observed between resisted and unresisted sprinting (2), but little is known about how neuromuscular activation is affected. This study compared lower-limb muscle activation between resisted and unresisted sprinting performed at equivalent running velocities.
METHODS:
Thirty-seven elite athletes performed two trials under three conditions: a 40-m maximal sprint without resistance and two motorised resisted sprints corresponding to loads equivalent to 25% and 75% of body mass in a sled configuration. EMG activity was recorded in the quadriceps, hamstrings, and gluteal muscle groups. ANOVA and statistical parametric mapping (SPM) were used to analyse EMG activity during the stance and swing phases for specific steps selected according to running velocities corresponding to 20%, 40%, and 60% decreases in maximal unresisted velocity (VDEC). Comparisons were performed between unresisted and 25% resisted conditions at 20% VDEC, across all conditions at 40% VDEC, and between the 25% and 75% resisted conditions at 60% VDEC.
RESULTS:
No significant differences in EMG activity were observed at 40% and 60% VDEC between the resistance conditions. At high running velocity (20% VDEC), significant differences were found between the unresisted and 25% resisted condition during the swing phase. Greater activation for unresisted sprint was observed for the biceps femoris long head (90–100%), the rectus femoris (35–45%), the semimembranosus and the semitendinosus (55–85%), and the vastus lateralis (60–85%) (all p < 0.05). No effects were observed during the stance phase.
CONCLUSION:
In line with Macchi et al. (1), both resistance and running speed appear to influence lower-limb muscle activation. However, when running velocity was comparable, differences were limited and observed only at the highest speed during the swing phase. This suggests that velocity remains the primary determinant of neuromuscular demand, while resistance induces only minor, phase-specific adjustments.

References
Macchi et al. MSSE 2025 ;57:1530-1545.
Da Silva et al. SJMSS 2025;35:e70174