Mental fatigue as a tool in sports and exercise evaluation of performance, perception, and brain activity. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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"Mental fatigue seems to be an underestimated and not well evaluated part of sports and exercises. When people become mentally fatigued, they usually experience difficulties in maintaining the task performance at an adequate level. Interventions which induce mental fatigue may help us to understand the complexity of fatigue and its influence in sports and exercise. Mental fatigue leads to temporary deterioration of attentional functioning, response readiness and increases in the number of behavioral errors. The working memory (WM) plays a prominent role in this context and can be measured by EEG (frontal Theta related to attention and parietal Alpha-2 spectral power related to information processing)."

This study evaluated if prolonged cognitive performances with high demands lead to mental fatigue demonstrated by changes in task performance, fatigue perception, and EEG power values. Right-handed males (N = 8) repeated five Rapid Visual Information Processing (RVIP) tasks (5 x 5 per minute). The Rapid Visual Information Processing task provided performance scores (reaction times, correct/incorrect/missed responses). After each block, Ss were asked to rate their mental fatigue using visual analogue scales. Before (rest) and during the tasks, EEG was measured in accordance with standards of the international 10:20 system from 13 scalp locations and divided into different frequencies. EEG power values were calculated and log-transformed.

Reaction time slowed over time and was associated with an increase in fatigue perception. Right hemispheric temporal Alpha-2 frequency demonstrated a fatigue effect with an increase in spectral power. Frontal Theta and parietal Alpha-2 power values demonstrated activation when compared to rest, but showed no significant effect due to mental fatigue.

Implication. Decreased performance and increased fatigue perception is accompanied by increased temporal Alpha-2 power which is associated with a decrease in mental activity, specifically a reduction of symbolic/verbal activity. Although EEG frontal Theta and parietal Alpha-2 power demonstrates an activation pattern, those changes are not related to the fatiguing task. If mental fatigue is to be used in performance fatigue studies it may be necessary to demonstrate mental fatigue not only in performance and perception but additionally at the brain level.

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