There is some evidence that exercise can enhance mood and even counter mild to moderate depression. Active people have a lower risk of stroke.
Starting an exercise program at any point in life boosts health. Activity helps older people remain active longer. Walking three to four hours a week reduces death by any cause by 54 percent even among people who have diabetes.
All these benefits vanish quickly once people stop exercising.
The Centers for Disease Control and Prevention and the American College of Sports Medicine set the standard for physical activity in 1995, recommending at least 30 minutes a day of moderate exercise on most or all days of the week, in increments as short as 10 minutes.
“ 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.”
One new study tested various combinations of high and moderate exercise intensity and duration, combined with a 30 percent reduction in calories consumed. The level of intensity produced no significant differences in weight loss. What did make a difference, the researchers say, was time.
Women who exercised 150 minutes a week lost 4.7 percent of their starting weight, while those who spent 200 minutes or more exercising lost 13.6 percent. 
Cheap, high-calorie foods and too much time in front of the TV or computer combine to fatten America’s children, say many experts. Nearly half of American youths age 12 to 21 get no regular vigorous exercise, says a U.S. Surgeon General’s report.
Meanwhile, older people want to exercise to improve their health and appearance, maintain their independence and remain active with their families. But they are discouraged by poor health conditions that interfere with ease of exercise, lack of time and the toll of aging.
Almost any form of physical activity can improve overall health and the cardiovascular system: walking, gardening, pushing a stroller, swimming laps, jumping rope, riding a bike. A “start low and go slow” approach is a good way to begin a personal exercise plan, experts say.
“The point is, at least do something,” Lee says. “Something is better than nothing.”