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Purpose: This study compared the effects of heavy resisted sprint training (RST) versus unresisted sprint training (UST) on sprint performance among adolescent soccer players. Methods: Twenty-four male soccer players (age: 15.7 [0.5] y; body height: 175.7 [9.4] cm; body mass: 62.5 [9.2] kg) were randomly assigned to the RST group (n = 8), the UST group (n = 10), or the control group (n = 6). The UST group performed 8 × 20 m unresisted sprints twice weekly for 4 weeks, whereas the RST group performed 5 × 20-m heavy resisted sprints with a resistance set to maximize the horizontal power output. The control group performed only ordinary soccer training and match play. Magnitude-based decision and linear regression were used to analyze the data. Results: The RST group improved sprint performances with moderate to large effect sizes (0.76–1.41) across all distances, both within and between groups (>92% beneficial effect likelihood). Conversely, there were no clear improvements in the UST and control groups. The RST evoked the largest improvements over short distances (6%–8%) and was strongly associated with increased maximum horizontal force capacities (r = .9). Players with a preintervention deficit in force capacity appeared to benefit the most from RST. Conclusions: Four weeks of heavy RST led to superior improvements in short-sprint performance compared with UST among adolescent soccer players. Heavy RST, using a load individually selected to maximize horizontal power, is therefore highly recommended as a method to improve sprint acceleration in youth athletes.
Derakhti, Bremec, Siethoff, and Psilander are with The Swedish School of Sport and Health Sciences, Stockholm, Sweden. Bremec is also with the SuperTrening Sport Performance Centre, Celje, Slovenia. Kambič is with the Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia; and the General Hospital Murska Sobota, Murska Sobota, Slovenia.