The 2008 Physical Activity Guidelines for Americans  are designed so people can easily fit physical activity into their daily plan and incorporate activities they enjoy.
These guidelines recommend that each week you do one of the following:
Make sure that you do at least 10 minutes of aerobic activity at a time.
In addition, incorporate muscle strengthening activities, such as weight training, push-ups, sit-ups, carrying heavy loads, or heavy gardening, at least two days a week.
Read about some specific recommendations for special conditions , such as women who are pregnant, adults with disabilities, and older adults or those with a chronic condition.
Exercise specialists, such as the American College of Sports Medicine, also recommend incorporating stretching and other exercises to increase flexibility and avoid injury, as well as exercises to improve balance and reduce risk of falls.
While exercise is undoubtedly beneficial, it is not true that the more exercise you do or the harder you work the body, the better the results. Too much or too arduous physical activity can lead to injury. It is essential to maintain a balance between working out the muscles without overdoing it.