Acute and chronic effects of high-intensity interval training (HIIT) on postexercise intramuscular lipid metabolism in rats

Abstract

Recovery from exercise refers to the period between the end of a bout of exercise and the subsequent return to a resting or recovered state. It is a dynamic period in which many physiological changes occur. A large amount of research has evaluated the effect of training on intramuscular lipid metabolism. However, data are limited regarding intramuscular lipid metabolism during the recovery period. In this study, lipid metabolism-related proteins were examined after a single bout of exercise in a time-dependent way to explore the mechanism of how exercise induces intramuscular lipid metabolism adaptation. Firstly, all rats in the exercise group underwent a five-week training protocol (HIIT, five times/week), and then performed a more intense HIIT session after 72 h of the last-time five-week training. After that, rats were sampled in a time-dependent way, including 0 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 96 h following the acute training session. Our results discovered that five weeks of HIIT increased the content of intramuscular triglyceride (IMTG) and enhanced the lipolytic and lipogenesis-related proteins in skeletal muscle. Furthermore, IMTG content decreased immediately post HIIT and gradually increased to baseline levels 48 h postexercise, continuing to over-recover up to 96 h postexercise. Following acute exercise, lipolytic-related proteins showed an initial increase (6-12 h) before decreasing during recovery. Conversely, lipogenesis-related proteins decreased following exercise (6-12 h), then increased in the recovery period. Based on the changes, we speculate that skeletal muscle is predominated by lipid oxidative at the first 12 h postexercise. After this period, lipid synthesis-related proteins increased, which may be the result of body recovery. Together, these results may provide insight into how the lipid metabolism-related signaling changes after chronic and acute HIIT and how protein levels lipid metabolism correlates to IMTG recovery.

Fig. 1

(A) The chronic and (B) acute effect of HIIT on intramuscular triglycerides abundance in gastrocnemius. Experiments were performed with control group (C, n=6), five-week HIIT group (CE, n=6), and acute training group (0 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 96 h; n=5/each time-point). Two replicates were used for each sample. The data were presented as the mean ± standard deviation. Each postexercise timepoint data are compared with CE and significant differences were analyzed with one-way ANOVA. * P<0.05.

Fig. 2

(A) Western blot analysis and (B) relative fold protein expression of p-CREB/CREB, p-AMPK/AMPK, and CPT-1b. Relative expression levels were normalized to GAPDH. The acute group’s protein level is normalized to GAPDH at first and then relative to the group of CE, which did not perform the acute training. Three bands are used for statistics. The data were presented as the mean ± standard deviation. Each postexercise timepoint data are compared with CE and significant differences were analyzed with one-way ANOVA. * P<0.05.

Fig. 3

(A) Western blot analysis and (B) relative fold protein expression of PPAR-γ, FASN, and TGF-β2. Relative expression levels were normalized to GAPDH. The acute group’s protein level is normalized to GAPDH at first and then relative to the group of CE, which did not perform the acute training. Three bands are used for statistics. The data were presented as the mean ± standard deviation. Each postexercise timepoint data are compared with CE and significant differences were analyzed with the one-way ANOVA. * P<0.05.