When an endurance athlete crosses the finish line of a race and collapses on the ground out of pure exhaustion, the majority of us assume that it is down to muscle fatigue and oxygen debt. However, the actual reason behind this display of fatigue may actually have more to do with our brains than our muscles!
We have known for quite some time that serotonin is released when we exercise, improving our mood and helping us to continue exercising. However, scientists have recently discovered that a surplus of serotonin actually triggers a braking mechanism in the brain known as central fatigue. In other words, serotonin is both the accelerator of exercise and the brake.
Central fatigue is a tiredness that affects the brain and nervous system as opposed to the muscles themselves. This slows us down to the point where we have to stop out of exhaustion, when without this mechanism our muscles could have continued for a much longer period of time. Scientists are researching ways of controlling serotonin levels in a bid to enhance endurance performance.
Cotel F, Exley R, Cragg SJ, Perrier J-F, Seratonin Spillover onto the Axon Initial Segment of Motoneurons Induces Central Fatigue by Inhibiting Action Potential Initiation, PNAS, 2013.