Effects of light-dark cycle manipulation on critical velocity and anaerobic running capacity in Wistar rats

The aim of the study was to assess the effect of the light-dark cycle on the critical velocity (CV) and the anaerobic capacity (ARC) of running rats. The entire experiment utilised two separate groups under two conditions: a regular light-dark cycle 12/12 hours (light on from 6:00 to 18:00 - RC group) and an altered light-dark cycle 12/12 hours (light on from 18:00 to 6:00 - AC group). First, running rat groups were selected. The animals were submitted to four exercise tests (25, 30, 35 and 40 m/min) performed until exhaustion. The times to exhaustion for each running intensity were recorded (tlim). The CV and ARC were estimated from the linear regression of 'velocity vs. 1/tlim', where the CV and ARC were the linear and slope coefficients, respectively. The running rat groups showed a significant difference in percent selection under the two light cycles (16.4% and 28.9% of running rats in the RC and AC groups, respectively). The CV was highest in the AC condition (CVRC = 22.7±0.8 m/min and CVAC = 25.5±0.4 m/min), but the ARC (ARCRC = 22.80±2.76 m and ARCAC = 21.80±4.93 m) and the linear fit (R RC 2 = 0.88±0.03 and R AC 2 = 0.85±0.02) were not different in both conditions These results indicate that caution is necessary when varying the circadian rhythm of rats submitted to running exercise, especially because their aerobic condition is improved when an altered light-dark cycle is used.