Purpose: The aim of the present study was to examine the changes in resisted sprint performance and kinematics provoked by different sled loads in elite sprinters and rugby players. Methods: Eight elite male sprinters and 10 rugby union players performed 20-m sprints under three loading conditions (0%, 20%, and 60% body-mass [BM]). Sprint time was measured in 0-5, 5-10-, and 10-20-m, while stride length and hip, knee, and ankle angles were measured using an eight-sensor motion analysis system at the same distances. Results: Sprinters were significantly faster than rugby players in unresisted and resisted sprints using 20% BM (effect size, “ES”[90% confidence limit, “CL”] range: 0.65[0.03;1.27]; 3.95[3.10;4.81]), but these differences were not significant at 60% BM. Compared to rugby players, sprinters showed lower velocity loss decrement in resisted sprints using 20% BM (ES[90%CL] range: 0.75[0.06;1.44]; 2.43[0.83;4.02], but higher velocity decrement loss using 60% BM (ES[90%CL] range: 1.13[0.43;1.82]; 1.46[0.81;2.11]). No significant differences were detected in stride length between sprinters and rugby players for any sprint condition (ES[90%CL] range: 0.02[-0.72;0.76]; 0.84[0.13;1.54]). Rugby players showed higher hip flexion in resisted sprints (ES[90%CL] range: 0.30[-0.54;1.14]; 1.17[0.20;2.15]) and lower plantar flexion in both unresisted and resisted sprints (ES[90%CL] range: 0.78[0.18;1.38]; 1.69[1.00;2.38] than sprinters. Conclusions: The alterations induced by resisted sprints in sprint velocity and running technique differed between sprinters and rugby players. Some caution should be taken with general sled loads prescriptions, especially when relative loads are based on distinct percentages of BM, as training responses vary among sports and individuals.
Fonte: International Journal of Sports Physiology and Performance, in press, 2021