Humans evolved to move — hunting, foraging, running, climbing, — and that movement promotes brain growth. This growth takes place especially in the prefrontal cortex, which is essentially your humanness. In Spark, The Revolutionary New Science of Exercise and the Brain, Dr. John Ratey explains it this way:

The real reason we feel so good when we get our blood pumping is that it makes the brain function at its best. The point of exercise is to build and condition the brain.” The reverse is also true, however: “What virtually no one recognizes is that inactivity is killing our brains… If your brain isn’t actively growing, then it’s dying.”

The studies are overwhelming. In 2011, The Mayo Clinic went through 1,600 papers on exercise and there was no disputing that exercise had a definite positive effect on memory, learning, performance, and motivation while reducing depression, age-related decline, and the risk of dementia and Alzheimer’s. Exercise also promotes neurogenesis and neuroplasticity, the pro­duc­tion of new neurons and con­nec­tions between neu­rons which helps keep your brain healthy and aids mental health. Ratey declares that “Exercise is the single most powerful tool you have to optimize your brain function.”