Homo Sapiens no longer needs to walk long distances, run, jump, or catch prey. Our bodies, however, still work best when we move. When we spend our days sitting, we get fat and... dumb.
"Spark" starts with a quote from Plato:
In order for man to succeed in life, God provided him with two means, education and physical activity. Not separately, one for the soul and the other for the body, but for the two together. With these two means, man can attain perfection.
The benefits of staying active are clear and are proven. Steady exercise: walking, running is essential. Sprinting works differently and is beneficial too. Physical activity that makes the brain work: karate, tennis, and other small team games are important from a different perspective. Exercising with others is better than doing it alone.
My favorite citation comes from page 237: "[...] if you are not busy living, your body will be busy dying."
John Ratey's web page.