Efeito de diferentes estratégias de aclimatação ao calor sobre as respostas termorregulatórias e o desempenho aeróbico de ratos submetidos a uma sessão de exercício em ambiente quente até a fadiga

Abstract

Introduction: Humans are homoeothermic animals that exhibit thermal adaptions when exposed passively or chronically to environmental heat, or when they perform chronical aerobic exercise in the heat or in temperate environments. These adaptations reduce thermoregulatory strain imposed by exercise in the heat. However, the effects of these different heat acclimatization strategies in rats, which represent an experimental model widely used in the study of the metabolic and central pathways involved in these adaptations, have not been investigated yet. Aim: To compare the effects of different heat acclimatization strategies on thermoregulatory responses and aerobic performance of rats subjected to a single bout of exercise in the heat. Methods: The rats were divided into four groups: two groups ran on a treadmill, one in the temperate environment (24°C, E24) and the other one in the heat (31°C, E31); and two groups that rested in the same environments (R24; R31). Each intervention consisted of 10 sessions (E groups, running at 60% of maximal speed for 40-48 min, R groups, 2 min running at 60% of maximal speed, followed by 38-46 min at rest). Before and after the 10 sessions, all the groups were subjected to a progressive exercise in the heat (31°C), when the aerobic performance and core body temperature (TCORE) and tail-skin temperature (TSKIN) were measured. Results: Time to fatigue, running distance and ΔTINT were higher, while ΔTCORE-to-km ratio was lower in E groups relative to R groups. These parameters were not influenced by the ambient temperature in which the interventions were performed. TSKIN was not different between groups after the 10 intervention sessions, indicating that the acclimation protocols did not modify cutaneous heat dissipation. Conclusion: Regardless of the ambient temperature in which the interventions were performed, heat acclimation protocols involving exercise were more efficient in reducing thermal stress and increasing aerobic performance during a progressive exercise until fatigue in the heat.