A biological process called AMP-activated protein kinase (AMPK), which boosts muscles, begins to fail with advancing age. This leads to a need for increased effort to achieve the same effects from exercise, and could help explain the link between aging and type 2 diabetes.
AMPK stimulates the body to burn off fat by producing mitochondria, the power sources of cells. The skeletal muscles of athletes have been found to contain a much higher number of mitochondria, which is likely linked to AMPK activity.
When scientists compared the skeletal muscle of 3-month-old rats and 2-year-olds, they found that AMPK was significantly slowed down in older animals. In addition, the muscle of young rats who did more exercise had double the normal AMPK activity, but this effect was not nearly as strong in older rats.
Older people have more fat in their muscles and livers than younger people do. These fat cells have been linked to insulin resistance and type 2 diabetes.