Nybo, Lars, and Bodil Nielsen. Perceived exertion is associated with an altered brain activity during exercise with progressive hyperthermia. J Appl Physiol 91: 2017–2023, 2001.—The present study tested the hypothesis that per-ceived exertion during prolonged exercise in hot environ-ments is associated with changes in cerebral electrical activ-ity rather than changes in the electromyogram (EMG) of the exercising muscles. Therefore, electroencephalogram (EEG) in three positions (frontal, central, and occipital cortex), EMG, rating of perceived exertion (RPE), and core tempera-ture were measured in 14 subjects during submaximal exer-cise in normal (18°C, control) and hot (40°C, hyperthermia) environments. RPE increased from 11 Ϯ 1 units at 5 min to 20 Ϯ 0 units at exhaustion (50 Ϯ 3 min) in the trial with progressive hyperthermia, whereas exercise in the control trial was maintained with a stable core temperature for 1 h without exhausting the subjects. Altered EEG activity was observed in all electrode positions, and stepwise forward-regression analysis identified core temperature and a fre-quency index of the EEG over the frontal cortex as the best predictors of RPE. In contrast, there were no significant correlations between RPE and any of the measured EMG parameters (median spectral frequency, root mean square, or amplitude), and the EMG parameters were not different in hyperthermia compared with control. Thus hyperthermia does not seem to affect the activation pattern of the muscles. Rather, the linear correlation among core temperature, EEG frequency index, and RPE indicates that alterations in cere-bral activity may be associated with the hyperthermia-in-duced development of fatigue during prolonged exercise in hot environments.
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