A "start low and go slow" approach is a good way to begin a personal exercise plan, experts say. "From the 1970s up to the 1990s, 'exercise' was geared to improving fitness and was based on the model of an athletic male college student," says Harvard's I-Min Lee, M.D. "Today, the new model is health, not athletic training." Almost any form of physical activity can improve overall health and the cardiovascular system. But many people who need exercise the most are kept from exercising due to poor health conditions that interfere with ease of exercise, lack of time or available facilities and the toll of aging or health conditions. "The point is, at least do something," Lee says. "Something is better than nothing."

Starting an exercise program at any point in life boosts health. Physical activity lowers body weight, cuts cardiovascular risk and blood pressure, improves cholesterol levels, has positive effects on the immune system and can reduce the risk of cancers. It strengthens the heart, helps the lungs function better, enables the blood to carry more oxygen, makes muscles stronger and improves motion in the joints. There is some evidence that exercise can enhance mood and even counter mild to moderate depression. Active people have a lower risk of stroke.