A recent study into the effects of resistance training on the aging process of muscle shows that it slows the effect of aging on muscle tissue. More specifically it helps preserve mitochondria in the muscle cell. Mitochondria are sometimes described as the "power house"  because they generate most of the cell's supply of ATP, used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in other tasks such as the control of the cell cycle and cell growth.

The study concluded that  not only will resistance exercise (lifting weights) help attain or maintain a healthy weight and reduce the risk of disability due to arthritis, this study now shows that it may actually reverse the biologic aging that takes place in muscle cells. 

To read more on this follow the link below

http://www.arthritis.org/research/funded-research/research-update/journal-summaries/exercise-reverse-aging/