Exercise significantly improves self-esteem and helps prevent depression. When you come home from work and feel stressed out, try walking vigorously for 30 minutes. It is amazing how much better you will feel. You'll also think and work better. When people claim they don't have time to exercise, I suggest they will get more done more quickly.
Exercise improves concentration, creative thinking, and sleep.
This may partially explain why the energy level improves so dramatically. That Immune System Exercise also improves the function of the immune system which can reap rewards from getting fewer colds to preventing cancer. Studies demonstrate that exercise reduces the incidence of a long list of diseases including specific cancers, heart attack, strokes, high blood pressure, diabetes and osteoporosis. The risk of dying from cancer declines sharply as exercise increases. The common comment You're too old to be doing that is really just plain bad advice.