The effect of vigorous treadmill exercise on adipose tissue development in the Zucker rat

Four-week-old male lean and obese Zucker rats were subjected to intense daily exercise for a 10-week period. The exercise regimen used (running 6 days/week for 90 min/day on a treadmill at 1.3 Km/h at an 8 per cent grade) was designed to maximize the amount of exercise performed. Lean and obese runners (LR and OR) gained significantly less weight than sedentary controls (LS and OS). Food intake was lower in LR and unchanged in OR compared with the control animals. Exercise increased adrenal weight in runners of both phenotypes. Gastrocnemius muscle weight was significantly higher in OR compared to OS. Despite the intense exercise regimen, carcass fat of OR was reduced only 12 per cent versus OS. In contrast, exercise decreased carcass fat by 32 per cent in LR versus LS. This decrease in body fat of LR was due to smaller adipocytes. Exercise did not affect adipocyte size in obese rats. However, OR had fewer carcass adipocytes. These results indicate that exercise had substantially different effects on adipose tissue cellularity of lean and obese rats. The results of the present study indicate that a program of intense treadmill exercise initiated immediately post weaning only modestly reduced adipose tissue growth in obese Zucker rats. Furthermore, it did not normalize body composition.