The Metabolic Adaptation to Exercise Following Intensity-Specific Aerobic Training in Female Rats

Limited research has examined the impact of training intensity on substrate utilization during acute exercise. Despite sex differences in the metabolic response to exercise, few studies have examined females.

This study compared the utilization of substrate during acute exercise following 8 wk of low-intensity (LoT) and high-intensity (HiT) aerobic training (AT) in female rats. It was hypothesized that both training programs would result in increased fat oxidation during acute exercise, with HiT demonstrating a higher shift toward fat oxidation.

Thirty-six female rodents were divided into four groups: sedentary control (Control), acute exercise only (AC), LoT, and HiT. The LoT and HiT groups performed progressive exercise up to an intensity of 21 and 36 m·min -1 , respectively. After training, the trained and AC groups performed an acute bout of 60-min exercise (30 m·min -1 ) and were sacrificed 30 min later.

Levels of epinephrine and protein kinase A activity were significantly higher ( P < 0.05) in both the trained and control groups. Both LoT and HiT exhibited higher muscle glycogen content in comparison to AC ( P < 0.05), suggesting muscle glycogen sparing in the trained animals. Moreover, hepatic glycogen in the HiT animals was significantly higher than LoT, suggesting that hepatic glycogenolysis was reduced. An increase in HSL activation in the HiT indicates a shift toward fat utilization during exercise and a directed role of protein kinase A to a preferable activation and utilization of fat.

These findings increase our understanding of various metabolic adaptations in response to different AT intensities in females.