Mental fatigue can affect physical...(h exercise sessions the researchers trac...)

Date:2/23/2009

h exercise sessions, the researchers tracked a variety of physiological measures, such as oxygen consumption, heart rate, cardiac output, blood pressure, ventilation, and blood lactate levels. The participants completed surveys to measure their motivation and perceived effort. The researchers offered monetary prizes for the best performance on the exercise and mental tasks as a way to keep motivation high.

Results

• The participants stopped exercising 15% earlier, on average, when they were mentally fatigued.
• The participants stopped at the same perceived effort level in both the fatigued and non-fatigued trial. However, mentally fatigued participants started at a higher level of perceived effort and reached the endpoint sooner.
• The cardio-respiratory and musculo-energetic measurements did not vary between the two trials when compared at specific points in time. However, because the non-fatigued trials went longer, heart rate and blood lactate levels were higher at the end of those trials.
• Motivation was the same in both trials and was not a factor.

The researchers speculate that the perception of effort occurs in the brain. Dr. Marcora said his team is considering two possibilities:

• mental fatigue lowers the brain's inhibition against quitting, or
• mentally fatigue affects dopamine, a brain chemical that plays a role in motivation and effort

One interesting note is that demanding mental tasks activate the anterior cingulate cortex of the brain. Previous research has shown that rats with a lesion in the anterior cingulate cortex would not work as hard for a reward compared to rats with no lesion. This area of the brain may be where perception of effort originates, Dr. Marcora said.

Applying the results

This research could provide a way to study chronic fatigue syndrome, Dr. Marcora said. People with chronic fatigue report they lack energy and expe
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Contact: Christine Guilfoy cguilfoy@the-aps.org 301-634-7253 American Physiological Society Source:Eurekalert

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