Cardiorespiratory and Metabolic Adaptations to a 6-Week High-Intensity Interval Training Program at Different Intensities in Young Soccer Players

This study compared the effects of high-intensity interval training (HIIT) prescribed at the respiratory compensation point (RCP) versus maximal aerobic speed (MAS) on cardiorespiratory and metabolic outcomes in young soccer players. Eighteen male national-level soccer players (15.7 ± .5 years) were randomly assigned to either the HIIT-RCP or HIIT-MAS group and completed a 6-week training program. The assessments included oxygen uptake (VO2) and running speed at the ventilatory anaerobic threshold and RCP, as well as relative buffering capacity, hypocapnic hyperventilation, blood lactate accumulation, and rate of perceived exertion. Significant improvements over time were observed in VO₂ max and running speed following the intervention (p < .05). Although no significant between-group differences were observed, moderate-to-large effect sizes were identified for VO2 and running speed at RCP and MAS, suggesting potentially relevant exploratory differences between interventions. Additionally, the HIIT-MAS group exhibited a greater increase in blood lactate, whereas rating of perceived exertion decreased over time in both groups. Both RCP- and MAS-based HIIT improved aerobic-related physiological variables following the 6-week intervention, with no significant between-group differences. These findings suggest that both HIIT prescription methods are effective options for enhancing aerobic fitness in youth soccer players.