80/20 Running: Run Stronger and Race Faster by Training Slower

by Matt Fitzgerald

We already know that inducing fatigue in the body through exercise triggers adaptations that make the body more resistant to fatigue in the future. Brain fatigue works the same way. Low-intensity runs lasting long enough to tire out the brain strengthen the parts of the brain that aid fatigue resistance. Shorter, faster runs aren’t as effective at fatiguing and strengthening these brain areas, which include the insular and temporal lobes, whose job is to perceive the physical elements of emotional states (such as the discomfort of extreme effort), and the anterior cingulate cortex (ACC), whose job is to resolve internal conflicts (such as the conflict between the desire to keep going and the desire to quit when one is running in a fatigued state). The stronger these areas become, the more slowly a runner’s sense of effort will increase in races and workouts and the longer he or she will be able to endure the agony of severe fatigue.