Being mentally fatigued can make people feel more exhausted when they exercise, according to researchers at Bangor University in Wales, U.K.
Their small study included 16 volunteers who twice rode a stationary bike until they were exhausted -- once when they were mentally rested and once when they were mentally fatigued, United Press International reported.
On average, the participants stopped exercising about 15 percent earlier when they were mentally fatigued. But the researchers found that mental fatigue didn't affect the performance of the heart or muscles. It was the participants' "perceived effort" that determined when they reached physical exhaustion while exercising.
The researchers suggested that mental fatigue may lower the brain's inhibition against quitting exercise, or may affect the brain chemical dopamine, which plays a role in motivation and effort, UPI reported.
The study appears in the March issue of the Journal of Applied Physiology.