Circadian rhythm of spontaneous activity and body temperature and its relationship with exercise capacity

The aim of this study was to verify relationships between circadian spontaneous activity and body temperature (T b ) with exercise capacity in two different phases of light/dark cycle. Circadian activity and T b of Wistar rats (n=11), under regular environmental conditions with free access to water and food, were continuously recorded using a telemetric sensor (G2 E‐Mitter) chronically implanted (ip) 3 days before. We accessed total time to fatigue, workload and T b during exercise. Animals were submitted to progressive exercise test protocols until fatigue during the early light and dark phases. Each test was separated for 3 days. Fatigue was set as the moment when rats couldn't keep pace with treadmill. Results suggest increased circadian dark phase activity compared to light phase (p<0.01). This was accompanied by greater light phase exercise capacity and T b variance and heat accumulation (p<0.05). There was no direct relationship of circadian activity and exercise capacity although at light phase a specific negative relationship of circadian temperature and exercise capacity was observed (r=−0.74, p<0.01). We demonstrated that circadian activity was not directly related to exercise capacity, despite the difference regarding exercise capacity and thermoregulation at two different circadian periods of rat activity. Supported by: CNPq and FAPEMIG