Impact of high-intensity interval training on cardiorespiratory fitness, body composition, physical fitness, and metabolic parameters in older adults: A meta-analysis of randomized controlled trials.

High-intensity interval training (HIIT) can effectively increase peak oxygen consumption, body composition, physical fitness, and health-related characteristics of adults; however, its impact in the older population remains highly debated. This review and meta-analysis aimed to evaluate the effects of high-intensity interval training on cardiorespiratory fitness, body composition, physical fitness, and health-related outcomes in older adults. Four electronic databases (PubMed, Scopus, Medline, and Web of Science) were searched (until July 2020) for randomized trials comparing the effect of HIIT on physical fitness, metabolic parameters, and cardiorespiratory fitness in older adults. The Cochrane risk of bias assessment tool was used to evaluate the methodological quality of the included studies; Stata 14.0 software was used for statistical analysis. HIIT significantly improved the maximum rate of oxygen consumption (VO2peak) as compared to a moderate-intensity continuous training (MICT) protocol (HIIT vs. MICT: weighted mean difference = 1.74, 95% confidence interval: 0.80-2.69, p < 0.001). Additional subgroup analyses determined that training periods >12 weeks, training frequencies of 2 sessions/week, session lengths of 40 min, 6 sets and repetitions, training times per repetition of >60 s, and rest times of <90 s were more effective for VO2peak. This systematic review and meta-analysis showed that HIIT induces favorable adaptions in cardiorespiratory fitness, physical fitness, muscle power, cardiac contractile function, mitochondrial citrate synthase activity, and reduced blood triglyceride and glucose levels in older individuals, which may help to maintain aerobic fitness and slow down the process of sarcopenia.