A umidade relativa do ar reduz o desempenho físico e aumenta o estresse térmico durante a corrida em intensidade autorregulada realizada em ambiente quente

Abstract

During prolonged exercises, such as endurance running competitions, the environmental conditions play an important role on physical performance of athletes. Several studies have evaluated the effects of ambient temperature on physical performance at different types of exercises; however, the isolated effects of relative humidity (RH) in a self-paced running exercise are still unknown. The aim of this study was to evaluate the effects of relative humidity on physical performance and thermoregulatory responses in a 10-km self-paced running exercise. Nine men (29.1 ± 3.6 years; 80.1 ± 8.4 kg; 176.9 ± 6.0 cm; 58.4 ± 7.2 mLO2.kg-1.min-1) underwent three experimental trials. In all of them they should run 10-km as fast as possible. The exercises trials were always performed at the same temperature (hot environment = 33°C), but with different relative humidity: 39%, 56% and 78%. The significance level was set at p<0.05. Physical performance in the 10-Km self-paced running exercise decreased in the 78% trial when compared to the 39 and 56% trials (78%: 54.60 ± 6.10 min; 39%: 49.93 ± 5.70 min; 56%: 50.05 ± 6.18 min), indicating that athletes had a lower average speed while running in the most humid condition . The pacing strategy adopted by the volunteers in the 78% trial was different from that of the 39% and 56% RH trials. From the 6th km until the end of the exercise, it was observed a fall in the average speed in the 78% situation compared to the 1st km and also compared to 39% and 56% situations. On the other hand, the average speed from the 1st km on was not different at any time in the 39% and 56% situations. Our findings show a detrimental effect of high relative humidity on physical performance in a 10-km self-paced running. Our results agree with previous studies that observed a lower time to exhaustion in a fixed intensity cycling exercise performed on a hot-humid environment. The athletes could not perform a final sprint, when running at 78% of relative humidity. Thermoregulatory, cardiovascular and psychological variables were also affected by the different relative humidity. Moreover, rectal temperature was higher in 78% trial from the 5th km until the end of exercise, which matches with the observed reduction in average speed. We conclude that in a hot environment (33°C) the higher relative humidity (78%) decreased physical performance, increased physiological strain and changed the pacing strategy of athletes in a 10-km self-paced running exercise.