The effect of a 12-week in-season combined training program on aerobic capacity of young soccer players

Abstract

Purpose: The purpose of this study was to examine the effects of a 12-week in-season combined training program on aerobic performance in young soccer players. Methods: Forty-eight U15 male soccer players (14–15 years) participated in this study. Participants were divided into three groups: a Combined Fitness Training Group (CFTG; n = 16), a Soccer Training Group (STG; n = 16), and a Control Group (CG; n = 16). The intervention was conducted during the competitive season and consisted of four weekly training sessions and one official match. The CFTG followed a combined training program in addition to soccer training with functional strength training, sprint development, change-of-direction (COD) drills, and intermittent aerobic training, while the STG followed a program with physical condition being trained only with soccer training. Aerobic performance was assessed using the Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IR1), recording performance level, final running velocity, total distance, and estimated VO₂max. A repeated-measures MANOVA (Group × Time) was applied. Results: Significant Group × Time interactions were observed for all aerobic variables (p < 0.001). The CFTG showed greatest improvements in Yo-Yo level (+25.83%), total distance (+62.64%), final velocity (+6.35%), and estimated VO₂max (+11.97%), with large to very large effect sizes (partial η² = 0.137–0.566). The STG showed smaller but significant improvements, whereas the CG demonstrated no meaningful changes. Conclusion: An in-season combined training program significantly enhances intermittent aerobic performance in young soccer players compared with soccer-only training. These findings support the integration of targeted conditioning strategies within competitive-season microcycles in youth soccer academies.