Effect of Low Volume Sprint Interval Training on Cardiorespiratory Fitness

Low levels of physical activity (PA) and cardiorespiratory fitness (CRF) are significant issues for societal health. Public health guidelines for adults recommend \> 150 min of moderate-intensity continuous training (MICT) or 75 min of vigorous exercise per week, and strength training on \> 2 days per week. However, in 2020, 75% of adult Americans did not meet these PA recommendations. Physical inactivity is the fourth leading cause of death worldwide, as it increases the risk of 40 chronic conditions. Low maximal oxygen uptake (V̇O2max; the gold standard index of CRF) is strongly associated with increased risk of future morbidity and all-cause mortality. In fact, many large-scale studies have reported V̇O2max to be a more powerful predictor of risk for future morbidity and all-cause mortality than more traditional risk factors such as smoking, hypertension, obesity, high cholesterol, and insulin resistance. For population-level health, the largest benefits from improved PA and CRF are gained by the least fit individuals, with even small increases in fitness shown to improve health. Despite exercise being the only viable means to improve V̇O2max, it remains underutilized for primary disease prevention. Nevertheless, adults do not engage in PA due to a perceived lack of time. High intensity interval training (HIIT) is a time-efficient form of PA requiring brief intense bursts of activity separated by rest periods. Empirical data show that HIIT elicits similar and in some cases superior benefits versus MICT, often with less time. A special type of HIIT is reduced exertion high intensity interval training (REHIT) requiring only two 20 second sprints within a 10 minute session. A few studies show that REHIT increases CRF and other health-related outcomes, yet these studies have been criticized due to their small sample size, which serves to question the broad application of REHIT in adults. The proposed randomized controlled trial will recruit 60 inactive adults to complete 24 sessions of REHIT and compare resultant changes in CRF, substrate metabolism, and psychological responses to a non-exercising control group. This sample size is threefold higher than used in prior work and provides adequate statistical power to detect meaningful increases in V̇O2max. The proposed study will advance further research in the area of HIIT and if successful, may promote inclusion of REHIT in PA recommendations as a feasible alternative or adjunct to moderate or vigorous-intensity exercise as promoted in current PA recommendations.