Contribution of spontaneous activity to daily energy expenditure of adult obese and lean Zucker rats.

The contribution of somatomotor activity to daily energy expenditure was estimated in 10-month-old, weight-stable, obese (fa/fa) and lean (Fa/?) Zucker rats. Total and resting heat production were assessed by recording oxygen consumption and stabilimeter activity each minute for five consecutive days in free-feeding animals. The number of activity counts, as well as their circadian pattern of occurrence, were highly similar in lean and obese groups. Likewise, the percentage of daily energy expenditure committed by the obese rats to activity was nearly identical to that of leans (19.3 vs. 19.7%, respectively). Observing these rats for one additional day under postabsorptive conditions produced similar estimates of their daily expenditure on activity. Thus, unlike prior estimates based on wheel-running behavior, continuous measurement of stabilimeter behavior indicates that both the proportion of daily expenditure on activity by fa/fa rats and its temporal pattern of occurrence are notably normal. Accordingly, it is concluded that maintenance of obesity in weight-stable adult obese Zucker rats does not depend upon a reduced expenditure on activity.