Physical activity has long been known to bestow such benefits as helping to maintain a healthy weight and reduce stress, not to mention tightening those abs. Now, a growing body of research is showing that regular exercise—as simple as a brisk 30- to 45-minute walk five times a week—can boost the body's immune system, increasing the circulation of natural killer cells that fight off viruses and bacteria. And exercise has been shown to improve the body's response to the influenza vaccine, making it more effective at keeping the virus at bay.
-At least two hours and 30 minutes a week of moderate-intensity, or one hour and 15 minutes a week of vigorous-intensity aerobic physical activity, or a combination of moderate and vigorous activity.
The National Runners Health Survey has shown the benefits of more—and more intense—exercise. Among its findings:
-To keep ahead of middle aged weight gain, runners need to increase their mileage by about 1.4 miles a week annually.
-Compared with merely satisfying the guideline activity levels, running 40 miles per week may reduce the risks of stroke by 69%, coronary heart disease by 37% and diabetes by 68%.
-Marathon runners enjoy greater cardiovascular benefits than non-marathon runners, even when their mileage is identical.
-Exercise intensity is associated with greater reductions in blood pressure and other cardiac risks.