Acute Exercise Increases Basal Spontaneous Physical Activity In Mice

PURPOSE: The benefit of exercise in the control and prevention of metabolic syndrome has long been linked to direct energy expenditure and resulting loss of unhealthy weight. While undeniably true, recent studies have proposed that another mechanism, spontaneous physical activity (SPA), may be a key mediator of exercise's metabolic benefit. Here, we present the findings of a study examining primarily the effects of acute exercise and secondarily the effect of Tirzepatide (TZP), an increasingly well-studied drug against metabolic syndrome, on the levels of spontaneous physical activity. METHODS: We examined the metabolic effects of high-fat diet (HFD; 12 weeks) in male C57BL/6 mice under treatment of once-weekly TZP (3 nmol/kg) or saline. Mice from each treatment group were further divided into exercise and non-exercise groups (n = 3/group). Mice in the exercise groups underwent 7 days of treadmill training, including a mid-regimen exercise capacity test. At both the beginning and end of the experiment, the mice were observed via metabolic cage to develop a profile of activity and metabolism. RESULTS: Analysis of locomotor activity data from the metabolic cage revealed an average increase in total SPA over a 24-hour period of 50% (45,719 clicks; P < 0.05) in all mice exposed to acute exercise post-intervention as compared to baseline. Furthermore, total SPA in all mice exposed to acute exercise was found to be, on average, 103% higher (70,124 clicks; P = 0.002) than mice who had not been exposed to exercise. These results were not associated with significant differences in body weight, food/water intake, or energy expenditure, lending credence to the specific impact of exercise on SPA. CONCLUSION: Based on these findings, we propose that exercise is a key behavioral regulator of the rate of SPA, and that this influence may be a key mechanism by which exercise exerts its benefit on metabolic health.