Whether you're working out at a gym or cycling outdoors, that dreaded moment of fatigue, when you just can't seem to get through it, feels the same. It turns out that some of that fatigue might be in your head. And knowing exactly where it occurs in the brain could lead to performance-enhancing therapies in the future, according to a recent study in Nature Communications.
The researchers recruited 20 participants for the study and asked them to repeatedly grasp and squeeze a sensor, varying their effort level from minimal to maximum force. Using MRI data and computer models, they found that feelings of fatigue appear to originate in the motor cortex , the area of the brain responsible for controlling movement, according to study co-author Vikram Chib.
As an additional measure to determine how this affects brain function, the researchers offered the participants two options to proceed. One was considered more "risky," setting the amount of effort based on a coin toss offering the chance of no effort or a predetermined level of effort. The "safe" option was just the default level.
By introducing uncertainty, the researchers were able to see how much each participant valued their effort. That offered insight into whether people would choose to keep going, even when fatigued.
How does fatigue influence our decisions?
Unsurprisingly, the researchers found that people tend to be more risk averse to avoid exertion. All but one of the participants chose the safe option, and the scans indicated that for all, the motor cortex was turned off during the decision-making process.
This is consistent with previous studies indicating that when people become fatigued, motor cortex activity decreases, which can lead to sending fewer signals to muscles, leading to a reduction in power during a hard sprint, for example.
Will these findings lead to hacking the motor cortex so that blows become a thing of the past? Not yet, but it's not impossible either.
Scientists believe we could use non-invasive brain stimulation to align motor cortex activity with an individual's performance expectations. Another approach is to introduce cognitive strategies that could alter how people perceive effort , potentially influencing motor cortex activity and making exertion feel less fatiguing.