Assisted Sprint Training: Individual Adaptations Linked to Force-Velocity Profiles and Spatiotemporal Variables.

Abstract

Abstract: Skujytė, A, Šilinskas, V, Trinkūnas, E, Lukonaitienė, I, Samozino, P, and Kamandulis, S. Assisted sprint training: individual adaptations linked to force-velocity profiles and spatiotemporal variables. J Strength Cond Res XX(X): 000-000, 2026-This study investigated the effects of a 6-week assisted sprint training (AST) program on sprint performance, spatiotemporal variables, and force-velocity profiles in youth soccer players and explored whether baseline regular sprint characteristics were associated with individual adaptations. Twenty-four players aged 16.5 ± 2.1 years were allocated to a fully AST, partially AST, or control group. Both assisted groups completed 12 sessions of 30-m towed sprints using a motorized device. Sprint performance was assessed under regular and assisted conditions before and after training, while the F-V profile was derived from regular conditions before training. Assisted sprint times improved significantly in the intervention groups (4.24 seconds [95% confidence interval: 4.16-4.33] to 4.10 seconds [95% confidence interval: 4.01-4.20]; ηp2 = 0.26), but regular 30-m sprint times and spatiotemporal variables did not change significantly. High responders displayed greater initial force and power capacities (theoretical maximal horizontal force, maximal propulsive power, maximal ratio of force) than nonresponders. Regression analysis indicated that maximal propulsive power and maximal ratio of force were the strongest predictors of improvement (adjusted R2 > 0.53 for both), whereas a theoretical maximal velocity showed a weak association (adjusted R2 = 0.13). Overall, AST improved performance only under assisted conditions, with the observed adaptations likely driven in part by sensorimotor adjustments. However, there was great interindividual variability. These findings highlight the relevance of force-velocity profiling for identifying potential responders and suggest that AST provides limited short-term transfer to regular sprint performance.