" It is important to understand that the duration of exercise matters far more than does the intensity of exercise with respect to the goal of enhancing fatigue resistance in the brain. What counts is not how hard the muscles are working but rather how long the brain is required to stay focused on the task at hand. In fact, research has shown that the brain can be fatigued at rest in a way that increases fatigue resistance and physical endurance. "

― Matt Fitzgerald , 80/20 Running: Run Stronger and Race Faster by Training Slower