Combined low-volume high-intensity interval training and inspiratory muscle training in patients with metabolic syndrome: A randomized controlled trial

BACKGROUND: Low-volume high-intensity interval training (LVHIIT) is known to improve cardiometabolic health; however, the potential additive effects of combining LVHIIT with inspiratory muscle training (IMT) in reducing the severity of metabolic syndrome (MetS) have not been fully explored. This study aimed to evaluate the effects of 8 weeks of IMT combined with LVHIIT on cardiorespiratory fitness, MetS parameters, and respiratory muscle function in individuals with MetS. METHODS: This randomized, controlled, double-blind trial included 38 adults with MetS, aged 42 to 60 years, who were randomly assigned to 3 groups: LVHIIT (n = 12), LVHIIT + IMT (n = 14), and control (n = 12). The primary outcome was the change in maximal oxygen consumption (VO2max) after 8 weeks. Secondary outcomes included MetS z-score, anthropometric measures, metabolic blood markers, and respiratory muscle strength and endurance. All outcomes were assessed at baseline and after the 8-week intervention. RESULTS: The mean age of participants was 50 ± 5 years, and 67% were women. Significant group × time interactions were observed for VO2max, oxygen uptake efficiency slope, heart rate recovery at 1 minute, waist circumference, hip circumference, visceral fat ratio, fasting plasma glucose, glycosylated hemoglobin A1c, and MetS z-score (P < .05). Both LVHIIT and LVHIIT + IMT groups showed significant improvements in VO2max (P < .001). Respiratory muscle strength and endurance increased significantly only in the LVHIIT + IMT group (P < .001). CONCLUSION: Eight weeks of LVHIIT combined with IMT led to improvements in cardiorespiratory fitness, respiratory muscle function, and key MetS components, including MetS z-score. Integrating IMT into LVHIIT may be an effective, clinically feasible, and time-efficient approach to improve cardiometabolic health in individuals with MetS in cardiac rehabilitation.