Resumen de Thermoregulation during exercise in the heat of American football players
Gabriela Tomedi Leites, Giovani dos Santos Cunha, Maurício Pechina, Juliana Lopes Teodoro, Raisa Vieira Branco Ozorio, Ronei Silveira Pinto
, Flávia Meyer
American football players might face challenges during a prolonged exercise in the heat which can lead to impairments in performance and induce heat-related illness. The purpose of this study was to verify the body temperature and sweating responses in American football players while exercising at a moderate-high intensity effort as prescribed by metabolic heat production. Seven heat-acclimatized players participated in the study. Players exercised 4×20-min bouts at moderate-high intensity as 8.0W.kg-1 of metabolic heat production, with 10min rest between them, totalizing 110min of heat exposure (39oC and 50% relative humidity). Rectal (Tre) and skin (Tsk) temperatures, heart rate (HR), metabolic heat production were measured continuously. Dehydration was calculated from Δbody mass pre-and post-exercise. Initial Tre and HR were 37.0 ± 0.3 °C and 80 ± 9 beats.min-1, respectively. Players began the trial euhydrated according to the initial urine specific gravity (1.014 ± 0.008) and colour (2.4 ± 1.4). During experimental trial, core temperature increased overtime (p < .001) resulting in a ΔTre of 2.2 ± 0.6 °C. Average HR during exercise was 166 ± 11 beats.min-1 and weighted Tsk was 36.7 ± 0.5 °C. Sweat volume was 2.6 ± 0.3 L, resulting a % hypohydration of -3.1 ± 0.4 % reflecting a moderate level of hypohydration. Final urine specific gravity and colour were 1.024 ± 0.009 and 5.0 ± 1.0, respectively. Experimental trials were interrupted at the end of the third and the fourth exercise bouts in two players due to the respective adverse conditions: leg muscle cramps, and excessive Tre increase (reached 39.9 °C). Thermoregulation and hydration must be a major concern, mainly related to greater exercise intensities and long-time practice, inducing high hypohydration levels and risk of hyperthermia.
