If you train long and hard enough, eventually you may hit a wall—the point when your muscles no longer work at peak performance, even though you still have more to give. But is running out of steam a product of a lack of energy (aka glycogen stores), or is something more at work?
Scientists have known about this kind of muscle fatigue—also known as “central fatigue”—for about 80 years, but a new study out of Denmark, published in the Proceedings of the National Academy of Sciences, sheds some light on what might prevent your muscles from working hard even when they have energy available.
It’s been long understood that when you exercise, your body releases serotonin, a neurotransmitter in the brain that acts like an accelerator to speed up the contraction of muscles. What the new research has uncovered, however, is that at higher levels, serotonin may become the opposite—a brake that slows down the firing of your neurons and keeps your muscles from overworking.
This research follows a 2011 study, from the journal Brain Research, that found that visual clues can play a role in muscle fatigue. Participants were asked to squeeze a ball until their hand became tired. In the second round, researchers used an optical illusion to fool them into thinking the hand was at rest. This time, their brain continued to send strong signals to the muscle to contract.
Will this new research into your brain’s role in fatigue help you get past the wall? Not right now—but it does get us one step closer to understanding why muscles tire and what keeps them going. And researchers also hope it can help combat doping. “It is crucial to identify which methods athletes can use to prevent central fatigue and thereby continue to perform beyond what is naturally possible,” study author Jean-Francois Perrier said in a release.