ABSTRACT
BACKGROUND: It is unclear whether autophagy mediates the long-term exercise adaptation of the skeletal muscle induced by high-intensity interval training (HIIT) . OBJECTIVE: To identify the influence of HIIT on skeletal muscle autophagy of middle-aged rats over time, and to understand the potential regulatory effects of autophagy on maintaining the muscle mass and improving aerobic capacity by HIIT. METHODS: Rats were randomly divided into quiet, moderate training group (50-minute running at the intensity of 60% VO2 max) and HIIT group (6 times of 3-minute running at 80% VO2 maxand 3-minute active recovery at 50% VO2 maxwith a 7-minute warm-up and a 7-minute cool-down at 60% VO2 max). All rats were tested for VO2 max, exhaustive running time and distance at baseline and after 4, 8 and 12 weeks of exercise, respectively. The soleus muscle were collected and weighted, and then the expression levels of autophagy-related protein Beclin 1, LC3 and P62 were detected by western blot assay. RESULTS AND CONCLUSION: The soleus muscle mass in the quiet group decreased at the 12thweek (P < 0.01), while the moderate training and HIIT groups improved this decline (P < 0.05). The HIIT group dramatically improved the VO2 maxfrom the 4thweek when compared with the pre-experiment and the quiet group, until the 12thweek. The expression levels of Beclin1 and LC3II in the quiet group declined at the 12thweek (P < 0.05, P < 0.001), but the expression level of LC3II and ratio of LC3II/LC3I raised from the 4thand 8thweeks till the 12thweek compared with the pre-experiment and the quiet group, and the expression level of LC3II and ratio of LC3II/LC3I point time significantly raised in the moderate training group at the 12thweek (P < 0.001, P < 0.01). In the quiet group, the content of P62 significantly increased at the 4th and 8thweeks (P < 0.05), and decreased at the 12thweek (P < 0.001), but the content of P62 remained at the low level in the moderate exercise and HIIT groups. These results imply that an equivalent or better effects on improving basic autophagy level, skeletal muscle mass and aerobic capacity of the middle aged rats,by HIIT versus moderate training,providing the theory and empirical data that highlight the role of HIIT in health promotion.