Motivation. Strength. Will power. Physical condition. Stamina. All of these have long been known to contribute the extent to which humans are able to voluntarily activate muscles. But for the first time, investigators have discovered neuronal processes that are responsible for reducing muscle activity during muscle-fatiguing exercise.

The investigators say their discovery opens up new areas of research to help people who experience muscle fatigue related to illness.

“The findings are an important step in discovering the role the brain plays in muscle fatigue,” said investigator and neuropsychologist Kai Lutz. “Based on these studies, it won’t just be possible to develop strategies to optimize muscular performance, but also specifically investigate reasons for reduced muscular performance in various diseases.”

In an earlier study, the researchers showed that nerve impulses from a muscle, much like pain information, inhibit the primary motoric area during a tiring, energy-demanding exercise.

In a second study, using functional magnetic resonance imaging, the researchers were able to localize the brain regions that exhibit an increase in activity shortly before the interruption of a tiring, energy-demanding activity—the thalamus and the insular cortex—and are thus involved in signalizing the interruption. Both of these areas analyze information that indicates a threat to an organism, such as pain or hunger.

The latest study indicates the inhibitory influences on motoric activity are mediated via the insular cortex. In tests using a bicycle ergometer, the researchers determined that the communication between the insular cortex and the primary motoric area became more intensive as fatigue progressed.

“This can be regarded as evidence that the neuronal system … not only informs the brain, but also actually has a regulating effect on motoric activity,” said investigator Lea Hilty.

Prolonged reduced physical performance is a symptom that is frequently observed in daily clinical practice, a press release noted. “It can also appear as a side effect of certain medication [and] … chronic fatigue syndrome is often diagnosed without any apparent cause.”

Results of the study were published in the European Journal of Neuroscience.

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