Associação entre a variabilidade da frequência cardíaca e o desempenho físico durante o exercício realizado em diferentes condições ambientais

Abstract

Physical exercise-induced cardiovascular responses result from changes in the activity of the autonomic nervous system. This regulation of the cardiovascular system can be indirectly established by the non-invasive analysis of the heart rate variability (HRV). This study aimed to investigate the relationship between HRV and physical performance during a single bout of exercise performed in different environments and verify whether the alterations on physical performance evoked by cold and hot environments were associated with modifications at HRV parameters. Initially, the volunteers (n = 9) were familiarized to the experimental trials. All exercises were performed on a cycle-ergometer positioned inside a climatic chamber that was adjusted to maintain the following ambient temperatures: 26ºC (temperate), 12ºC (cold) and 40ºC (hot), with relative air humidity always set at 50%. The volunteers were subjected to three modified Balke tests to establish their maximal power output (Pmax) in each environment. Furthermore, the volunteers were subjected to fatiguing, prolonged exercises (these exercises started at 40% of Pmax, with increments of 2% of Pmax every 8 minutes) in the three above-mentioned environments. Physical performance during prolonged exercises was impaired in hot, but facilitated in the cold environment. The variance parameter of HRV calculated when subjects were resting showed a positive and significant correlation with total exercise time at 12°C. In the first stage of prolonged exercise, the pulse interval (mean) of heart rate was positive and significantly correlated with physical performance at 40°C. Regarding the second stage, the very low frequency (VLF) and high frequency (HF) components showed, respectively, negative (at 26°C) and positive (at 40°C) correlations with physical performance. We then tried to correlate the percentage changes in HRV parameters with the percentage changes in performance induced by exposition to cold or hot environments; however, no significant correlations were observed. In our study, the HRV analysis performed in resting and during the first two stages of prolonged exercise cycling was not a useful tool for predict acute physical performance, once few parameters of HRV was significantly associated with the total time of exercise in each one the three studied-environments.