Mental Fatigue Can Affect Physical Performance
For nearly the first century of its existence, the discipline of exercise science all but ignored the brain, deeming it peripheral to exercise performance. The situation began to change in the 1990s, when Timothy Noakes of the University of Cape Town, South Africa, formulated his "central governor" theory of exercise performance, which posited that the brain in fact played a primary role in the regulation of physical exertion. Since that time, Noakes and others have concocted all kinds of experiments to test this hypothesis, and most of them have validated it.
Now researchers from Bangor University in the United Kingdom have performed a study that tested the central governor hypothesis in such a simple way, one wonders why it was not done years ago. The study design was based on the premise that if exercise fatigue originates in the brain, as the central governor theory holds, then a tired brain should be unable to drive the body to perform at the same level in an exercise test as a non-fatigued brain. Sixteen participants rode stationary bikes to exhaustion on two occasions: once after completing a 90-minute mental challenge designed to produce mental fatigue and once after watching documentary films for 90 minutes, which of course was not mentally fatiguing. On average, the participants were able to continue cycling 15-percent longer in the mentally fresh trial than in the mentally fatigued trial.
All of the physiological measurements taken were basically the same in both trials, but subjects started at a higher rating of perceived exertion (RPE) in the mentally fatigued trial. In other words, the same intensity of exercise felt harder from the beginning when the subjects were mentally tired. Previous research has shown that perceived exertion is the key predictor of exercise fatigue. Although RPE is closely linked to physiological variables such as heart rate and blood lactate levels, it is not absolutely determined by them, as this study shows. And it appears that, in this study, fatigue within the brain rendered the organ less able to drive muscle activity, and this was the source of the higher initial RPE that caused the subjects to quit earlier in the mentally fatigued trial. |
