Acute Effects of Assisted and Resisted Sprint Training on Subsequent Sprint Performance: A Systematic Review and Meta-Analysis.

Abstract: Xu, K, Yin, M, Zhong, Y, Huang, K, Xu, Y, Zhou, J, and Wang, R. Acute effects of assisted and resisted sprint training on subsequent sprint performance: A systematic review and meta-analysis. J Strength Cond Res 39(5): e711-e720, 2025-The aim of the meta-analysis was to determine the acute effects of resisted (RST), assisted (AST), and unresisted (UST) sprint training on sprint performance and to identify the optimal training protocol. A computerized search was conducted in 5 databases, resulting in the inclusion of 23 studies and 395 subjects. The findings indicated that RST acutely improved sprint performance (effect size [ES] -0.20; p < 0.05), while UST (ES = -0.03) and AST (ES = -0.18) did not produce significant improvements (p > 0.05). Subgroup analyses revealed that RST load as a percentage of body mass (%BM) showed the greatest improvement with heavy loads (50-75% BM, ES = -0.40) compared with light (0-19% BM, ES = -0.22), moderate (20-49% BM, ES = -0.21), and very heavy (>75% BM, ES = 0.10) loads. Further analyses indicated that sled pushing (ES = -0.60) was more effective than sled pulling (ES = -0.34) under heavy load RST conditions. Nonlinear meta-regression results demonstrated that sprint performance improvement exhibited an inverted-U relationship with RST load. In addition, heavy load RST and moderate load AST did not disrupt subsequent sprinting technique. In conclusion, only RST acutely improved subsequent sprint performance, whereas AST and UST did not. For optimal results with RST, it is recommended to use 1 set of heavy loads (50-75% BM) for sled pushing for a distance of 15-20 meters, followed by a rest period of 4-8 minutes before performing 0-30 meters of UST.