BACKGROUND: High-intensity interval training (HIIT) has been shown to improve cardiometabolic health during supervised lab-based studies but adherence, enjoyment, and health benefits of HIIT performed independently are yet to be understood. We compared adherence, enjoyment, and cardiometabolic outcomes after 8 weeks of HIIT or moderate-intensity continuous training (MICT), matched for energy expenditure, in overweight and obese young adults. METHODS: 17 adults were randomized to HIIT or MICT. After completing 12 sessions of supervised training over 3 weeks, participants were asked to independently perform HIIT or MICT for 30 min, 4 times/week for 5 weeks. Cardiometabolic outcomes included cardiorespiratory fitness (VO peak), lipids, and inflammatory markers. Exercise enjoyment was measured by the validated Physical Activity Enjoyment Scale. RESULTS: Exercise adherence (93.4 +/- 3.1% versus 93.1 +/- 3.7%, respectively) and mean enjoyment across the intervention (100.1 +/- 4.3 versus 100.3 +/- 4.4, respectively) were high, with no differences between HIIT and MICT (p > 0.05). Similarly, enjoyment levels did not change over time in either group (p > 0.05). After training, HIIT exhibited a greater decrease in low-density lipoprotein cholesterol than MICT (-0.66 mmol/L versus -0.03 mmol/L, respectively) and a greater increase in VO2peak than MICT (p < 0.05, +2.6 mL/kg/min versus +0.4 mL/kg/min, respectively). Interleukin-6 and c-reactive protein increased in HIIT (+0.5 pgm/L and +31.4 nmol/L, respectively) and decreased in MICT (-0.6pgm/L and -6.7 nmol/L, respectively, p < 0.05). CONCLUSIONS: Our novel findings suggest that HIIT is enjoyable and has high unsupervised adherence rates in overweight and obese adults. However, HIIT may be associated with an increase in inflammation with short-term exercise in this population.

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