EEG-Related Changes to Fatigue during Intense Exercise in the Heat in Sedentary Women

Abstract

Purpose: This study examined the possible causal mechanisms of fatigue during intense exercise in the heat in a group of nine sedentary women. Methods: Two strenuous cycling sessions were performed, at 100% of maximal aerobic power, either in neutral (N-Ex, air temperature: 22°C ± 0.4°C, air humidity: 53% ± 8%) or in heat conditions (H-Ex, air temperature: 35°C ± 0.3°C, air humidity: 59 ± 6). Tympanic temperature (Tty), heart rate (HR), body mass loss (BML), lactate concentration [La] and brain electrical activity (EEG: α and β waves and α / β ratio) were recorded. Results: Tty, HR and [La] increases (p < 0.001) did not differ significantly between conditions. However, Tty increase rate was significantly (p < 0.05) higher during H-Ex (0.12 ± 0.03°C·min ﹣1 ) than that during N-Ex (0.08 ± 0.02°C·min ﹣1 ), and time to exhaustion (Time Limit at 100%) was significantly (p < 0.01) decreased (﹣18% ± 4%) during H-Ex session. Under both conditions, β waves decreased (p < 0.05) and α / β ratio increased (p < 0.05) significantly immediately before exhaustion. Conclusion: During exercise in the heat, the high rate of core temperature rising might be a critical factor triggering faster brain changes.