How Much Physical Exercise?

For adults who are generally fit and are 65 years of age or older, at least 2 ½ hours of moderate-intensity aerobic activity is needed every week plus muscle-strengthening activities on two or more days a week that work all major muscle groups. On the bright side, you can spread your activity out during the week, into small blocks of time of at least 10 minutes. What counts as moderate-intensity aerobic activity is breathing harder with your heart beating faster. On a scale of 0 for sitting and 10 for working very hard, aim for a 5 or 6 on the scale. What counts as muscle-strengthening activities is working with resistance bands or doing exercises that use your body weight for resistance. Yoga counts as well. Doing 8 to 12 repetitions per activity counts as a set; doing 2 to 3 sets gives the most benefit.

http://www.cdc.gov/physicalactivity/basics/older_adults/