Exercise Snacks are a Time-Efficient Alternative to Moderate-Intensity Continuous Training for Improving Cardiorespiratory Fitness but not Maximal Fat Oxidation in Inactive Adults: A Randomized Controlled Trial

The aims of this study were (1) to determine how stair-climbing-based exercise snacks (ES) compared to moderate-intensity continuous training (MICT) for improving cardiorespiratory fitness (CRF), and (2) to explore whether ES could improve maximal fat oxidation rate (MFO) in inactive adults. Healthy, young, inactive adults (n = 42, Age: 21.6 ± 2.3 years, BMI: 22.5 ± 3.6 kg/m2, peak oxygen uptake [VO2peak]: 33.6 ± 6.3ml·kg−1·min−1) were randomly assigned to ES, MICT or Control. ES (n = 14) and MICT (n = 13) groups performed 3 sessions per week over 6 weeks, while the control group (n = 15) maintained their habitual lifestyle. ES involved 3 × 30 s ‘all-out’ stair-climbing (6 flight, 126 steps, 18.9 m total height) bouts separated by >1-h rest, and MICT involved 40 min × 60-70% HRmax stationary cycling. A significant group × time interaction was found for relative VO2peak (p < 0.05) with ES significantly increasing by 7% compared to baseline (MD = 2.5 ml·kg−1·min−1 [95% CI = 1.2, 3.7], Cohen’s d = 0.44), while MICT had no significant effects (MD = 1.0 ml·kg−1·min−1 [-1.1, 3.2], Cohen’s d = 0.17), and Control experienced a significant decrease (MD = -1.7 ml·kg−1·min−1 [-2.9, -0.4], Cohen’s d = 0.26).MFO was unchanged among the three groups (group × time interaction, p > 0.05 for all). Stair climbing-based ES are a time-efficient alternative to MICT for improving CRF among inactive adults, but the tested ES intervention appears to have limited potential to increase MFO.