Exercise for the Mind

'We all know that exercise makes us feel better, but most of us have no idea why. We assume it's because we're burning off stress or reducing muscle tension or boosting endorphins, and we leave it at that. But the real reason we feel so good when we get our blood pumping is that it makes the brain function at its best, and in my view this benefit of physical activity is far more important--and fascinating--than what it does for the body. Building muscles and conditioning the heart and lungs are essential side effect. I often tell my patients that the point of exercise is to build and condition the brain.'
--from an introduction to Spark--The Revolutionary New Science of Exercise and the Brain, by Harvard Medical School psychiatrist professor John Ratey.