Strategies for Sustained Exercise in Obesity Management: Physiological Effects of High-Intensity Interval Training and Detraining Intensity Levels

This study investigated the effects of high-intensity interval training (HIIT) and exercise intensity during a detraining period on mitochondrial biogenesis and muscle hypertrophy-related proteins in obese mice. Obesity was induced in C57BL/6 mice by feeding a high-fat diet (HFD) for 10 weeks, followed by 8 weeks of HIIT. During a 4-week detraining period after HIIT, mice were assigned to one of six groups: control (CG), low-intensity (LID), or moderate-intensity (MID) exercise groups at either 2 or 4 weeks of detraining. In the soleus muscle, the expression levels of PGC-1α and FNDC5 significantly increased following HIIT (PGC-1α: p=0.002; FNDC5: p=0.002) but decreased significantly during the detraining period in both CGs at 2 and 4 weeks. In contrast, LID at both 2 and 4 weeks, as well as MID at 4 weeks, maintained significantly higher levels of both proteins compared to the CG (p<0.01). In the gastrocnemius muscle, the expression of PI3K, Akt, and mTOR significantly increased after HIIT (all p<0.001) but decreased during the detraining period. However, these expression levels were significantly preserved in both the LID and MID groups at 2 and 4 weeks. These findings suggest that low- and moderate-intensity exercise during the detraining period can help preserve mitochondrial function and muscle protein synthesis signaling, thereby mitigating the negative consequences of exercise cessation in obese mice.