Avaliação do exercício induzido e da atividade física espontânea: efeito dual do fotoperíodo

Abstract

Physical performance is directly influenced by thermal balance. Given the influence of circadian rhythms in homeostasis control, the impact of the biological clock in performance has attracted the interest of several research groups. In the present study, we sought to investigate the relationship between daily fluctuations of internal body temperature (Tcore) and spontaneous locomotor activity (SLA) with the workload (W) performed during a progressive treadmill exercise test. The thermoregulatory and neural responses induced by graded exercise until fatigue were also evaluated. In order to perform photoperiod-related analysis, adult Wistar rats (n = 23) had their levels of Tcore and SLA continuously recorded by telemetry during 48 hours (light / dark cycle: 14/10 h). Later, a group of animals was subjected to a protocol of progressive exercise until fatigue during light and dark phases (n = 11). Another group resting on the treadmill was used as control (n = 12). Inboth groups, Tcore, tail skin temperature and ambient temperature during each experimental session were recorded. A third group (naif), without any prior manipulation, was used as an intact control (n = 12). At the end of the last experimental session, the animals were perfused and the brains removed for immunohistochemical analysis of neuronal activation in the PVN, SO, SQN and LC. The results showed a direct correlation between SLA and the change of Tcore (r = 0.88 and p<0.001) as well as a daily oscilation of the ratio between these variables (p<0.001). The W was 23% higher in the light phase (p<0.001). Besides, the difference in performance was accompanied by a lower initial Tcore (p<0.01) and an increased ability to accumulate heat during light phase exercise (p<0.01). Only fatigue activated PVN, SO and LC, independent of time of the day (p<0.001). The SQN was not activated neither by exercise nor time of the day. It was also observed an intrinsic component, regardless of the phase of the day of both induced-exercise (r=0.91 and p<0.0001) and SLA (r=0.59 and p<0.001). However, this association did not occur between the two manifestations of locomotor activity. Taken together, these results suggest the existence of a dual mechanism of control and regulation dependent of the type of locomotor activity. Thereafter, the phase of the cycle, possibly through its centrally mediated mechanisms on internal body temperature and physical activity fluctuations, favors physical performance during light phase independent of lower basal spontaneousactivity levels.