Increases in Physical Activity Result in Diminishing Increments in Daily Energy Expenditure in Mice

Exercise is a common component of weight loss strategies, yet exercise programs are associated with surprisingly small changes in body weight [1–4]. This may be due in part to compensatory adaptations, in which calories expended during exercise are counteracted by decreases in other aspects of energy expenditure [1, 5–10]. Here we examined the relationship between a rodent model of voluntary exercise— wheel running— and total daily energy expenditure. Use of a running wheel for 3 to 7 days increased daily energy expenditure, resulting in a caloric deficit of ∼1 kcal/day; however, total daily energy expenditure remained stable after the first week of wheel access, despite further increases in wheel use. We hypothesized that compensatory mechanisms accounted for the lack of increase in daily energy expenditure after the first week. Supporting this idea, we observed a decrease in off-wheel ambulation when mice were using the wheels, indicating behavioral compensation. Finally, we asked whether individual variation in wheel use within a group of mice would be associated with different levels of daily energy expenditure. Despite a large variation in wheel running, we did not observe a significant relationship between the amount of daily wheel running and total daily energy expenditure or energy intake across mice. Together, our experiments support a model in which the transition from sedentary to light activity is associated with an increase in daily energy expenditure, but further increases in physical activity produce diminishingly small increments in daily energy expenditure. [Display omitted] •Introduction of a running wheel increased daily energy expenditure in mice•This plateaued after 1 week, despite further increments in wheel use•The amount of wheel use did not correlate with total daily energy expenditure O’Neal et al. examined the relationship between the amount of voluntary wheel running and total daily energy expenditure. They report that increases in voluntary wheel running were associated with diminishingly small changes in energy expenditure. As a result, the amount of wheel use was not correlated with total daily energy expenditure in mice.