Muscle Mass is Metabolic Currency
Just as financial wealth allows you the freedom to go and do, muscle tissue is the currency that sustains a healthy metabolism and structure. Research shows that a gain in muscle mass will actually reverse some of the markers of aging; this is due to an improved insulin sensitivity and an increase in functional capacity. Any significant loss of muscle mass will result in a decrease of functional capacity.
The real benefits of exercise are realized through muscle adaptation; as you gain muscle, you gain functional capacity and a reversal of aging.