RESPOSTAS METABÓLICAS E TERMORREGULATÓRIAS DURANTE UMA MEIA MARATONA EM AMBIENTE ABERTO.

Abstract

The present study aims to describe the metabolic and thermoregulatory conditions during a 21km race in warm environment with self - regulated intensity. Methods: A descriptive, observational study was conducted with recreational male runners. The sample was non-probabilistic for convenience with ten runners of 33.40 ± 10.04 years, body mass of 66.40 ± 9.15 kg, height of 1.71 ± 0.06 m, body mass index of 22.58 ± 2.05 kg/m2. The maximum oxygen consumption obtained in the test was 58.57 ± 5.47mL.kg¹.min¹, and the volunteers had a weekly training frequency of five days with a mean mileage of 62.5 ± 28.8km. The 21km race was conducted individually under solar radiation on a predetermined course and marked every 3000 meters, with ambient temperature (TA) of 27.96 ± 1.70 °C, air temperature (TG) of 28.52 ± 2.51 °C, relative humidity (IAR) of 76.88 ± 7.49% and Index of Globe Temperature and Wet Bulb (IBUTG) of 25.80 ± 1.18 °C. Oxygen consumption was obtained from a portable metabolic analyzer and the mean values expressed every 3km throughout the race. Measurements of skin temperature performed by a laser-guided thermometer at different points were measured two minutes before the start, every 3 km and immediately at the end of the race. The internal temperature was measured by the CorTemp capsule system every 3km. The race had hydration points ad libitum every 3km. For all tests the level of statistical significance was used P value <0.05. The normality of the data was analyzed through the Shapiro-Wilk test. Comparisons of the measurements before and during the 21km race were made through the one-way ANOVA test, with Tukey's post hoc test. To compare the PSE variable a nonparametric analysis was used with Friedman's hypothesis test to verify difference over time and when found difference was used the Wilcoxon test. All statistical analyzes were performed by SigmaPlot software version 11.0. Results: Participants completed the 21km race in 101: 00 ± 9:52 minutes which corresponds to 12.93 ± 7.83% higher than the best average time already reached in official half marathon events (p = 0.02). The average race pace of the volunteers during the 21km race was 4:50 min/km. The mean oxygen consumption of the participants during the 21km race was 40.93 ± 5.09ml/kg/min, corresponding to 70.25 ± 11.06% of the VO2peak. The internal temperature increased to the sixth kilometer, and then had stable behavior until the end of the 21km race. In addition, the mean temperature of the head and skin showed a reduction of the measured regions (top of head, forehead, cheek, chest, arm and thigh), the top temperature of the head was the lowest (31.2 ± 2.11 °C) and that of the forehead was the largest (33.7 ± 1.35 °C). Conclusion: During a 21-km run in hot and humid outdoor environment with self-regulated intensity the increase in internal temperature and heart rate occurred within acceptable limits even with moderate dehydration. From the third kilometer starts a reduction in the speed of running that resulted in the sixth kilometer of a smaller production of heat, causing that the internal temperature remained above 39 ° C.