
As we age our metabolism slows down. This can be prevented to some degree by increasing lean muscle mass.

Individuals who weight 130-200lbs can expect to burn 400-700 calories or more in an 1 hour circuit training program.
People who engage in 90 minutes of physical activity a week have a 20% reduction in mortality risk. Excercising 150 minutes per week will reduce moratlity risk by 30% & 420 minutes a week has a whopping 40% reduction in moratality risk compared to those who are sedentary!
As of 2010, new research shows that aging women who want to maintain a healthy weight need to exercise for at least an hour a day.