Determinantes da hipertermia durante o exercício físico extenuante: uma abordagem translacional

Abstract

Although the increase in core body temperature (TCORE) favors physiological responses during physical exercise, severe hyperthermia is associated with reduced performance and increased occurrence of heat illnesses. The first objective of the thesis was to systematically review the studies that investigated the TCORE of rats submitted to treadmill exercise to understand the factors that influence the TCORE achieved in fatigue/exhaustion. In this review, multiple linear regression analyses were performed on data extracted from studies that used both exercises with incremental speed increase and exercises with fixed speed. The systematic review indicated that the TCORE values obtained in fatigue/exhaustion were mainly explained by ambient temperature, initial TCORE (pre-exercise), and parameters related to physical performance (i.e., distance covered in incremental exercises and duration in constant exercises). The second objective of the thesis was to understand the factors that influence the increase of different indices (cerebral, abdominal, and colonic) of TCORE in rats submitted to progressive exercise until fatigue. Three hundred and seventy individual records were analyzed using hierarchical multiple linear regressions, which revealed that the magnitude of hyperthermia in rats submitted to incremental running depends mainly on ambient temperature, physical performance, and initial TCORE, regardless of the temperature measurement site. These results corroborate the findings of the systematic review. The third objective of the thesis was to identify the determinants of the increase in TCORE in individuals submitted to a 10 km time trial under conditions of environmental heat stress. Seventy-five individual records were analyzed using hierarchical multiple linear regression, which showed that exercise-induced hyperthermia in runners depends primarily on initial TCORE, environmental conditions, and running speed. We concluded that the main determinants of hyperthermia induced by strenuous exercise are environmental conditions, initial TCORE, and parameters related to physical performance. Interestingly, these findings were similar in rats and humans, indicating the possibility of translating specific results between the two species.