http://articles.mercola.com/sites/articles/archive/2007/02/27/why-exercising-as-you-age-becomes-more-important-and-challenging.aspxA 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 agingenCommunityServer 2008.5 SP1 (Build: 31106.3070)