Effects of eight weeks of respiratory muscle training combined with high-intensity interval training on respiratory muscle strength, intermittent running performance, and agility in soccer players

This study examined whether adding respiratory muscle training (RMT) to high-intensity interval training (HIIT) provides additional benefits for respiratory muscle strength, intermittent running performance, and agility in male soccer players. Twenty-six players were randomly allocated to a control group (n = 8), a HIIT group (n = 9), or an RMT+HIIT group (n = 9). The intervention lasted 8 weeks. All groups maintained their usual weekly schedule of five soccer training sessions and one competitive match. The control group received no additional intervention; the HIIT group completed two weekly running-based HIIT sessions; and the RMT+HIIT group completed the same HIIT protocol plus supervised RMT three times per week at 40% of maximal inspiratory pressure. Respiratory muscle strength, Yo-Yo IR1 performance (total distance, repeated shuttle runs, and derived estimated VO₂max), and Illinois Agility Test time were assessed before and after the intervention. Significant time × group interactions were observed for all outcomes. Baseline-adjusted analyses showed greater improvements in MIP, MEP, and Yo-Yo IR1-derived outcomes in RMT+HIIT than in both control and HIIT. Both HIIT and RMT+HIIT improved Illinois Agility Test performance compared with control, with no difference between the intervention groups. These findings indicate an additional benefit of RMT when added to HIIT for respiratory muscle strength and intermittent running performance. Practically, low-volume RMT may be added to HIIT-based soccer conditioning when these outcomes are training priorities.