The benefits of exercise are numerous and substantial. Exercise is associated with better mental function, lower emotional stress, lower weight, reduced bone thinning, lower risk of diabetes and heart disease, lower risk of certain cancers, and steadier balance. It is also associated with longevity. The figure below is from one typical study which demonstrates that the fitter one is, the better the survival over time. One key point is that the biggest difference was between the lowest performing group and the second lowest group, who were still below average. In other words, small improvements in physical conditioning for those in the worst shape have large benefits.

The CDC recommends at least 150 minutes of moderate aerobic activity, such as brisk walking, biking, swimming, bike riding on flat or moderately hilly terrain, doubles tennis and mowing the lawn, each week. Alternatively, you could perform 75 minutes of vigorous aerobic activity, such as singles tennis or running, a week. You can be creative, climbing stairs rather than taking the elevator at work or parking far from the store entrance when shopping. In addition to aerobic activity, do strength training exercises for the major muscle groups at least two times a week. Strength training can be achieved using weight machines, your own body weight, heavy bags, or resistance tubing. 

The following table illustrates the benefits of a healthy lifestyle on longevity. Harvard researchers followed 120,000 men and women over more than three decades. They were assigned points for 1) never smoking 2) drinking less than one 5 oz glass of wine or its equivalent daily for women and two glasses for men 3) exercising moderately for at least 150 minutes a week 4) eating a healthful diet and 5) having a normal weight. Those with zero points were the baseline to whom the other groups were compared. As the table shows, compared to those with zero points, those with five points had 26% the chance of dying during the study.