From Ouroboros: "AMP-activated kinase (AMPK) agonists mimic the effects of exercise, raising the possibility of a 'workout pill' that could simulate the effects of vigorous activity. The applications to human health are, to mildly understate the case, significant; it sounds almost too good to be true, and it leaves one looking for the catch. ... it turns out that AMPK is activated by certain types of genotoxic stress, and contributes to UV-induced apoptosis in the skin ... activation of AMPK could exacerbate the pro-aging effects that UV light exerts on the skin. Judging from the peroxide results, this also applies to endogenously generated reactive oxygen species (ROS) - which one can't avoid by simply staying out of the sun. Before we panic and throw the exercise mimetic baby out with its carcinogenic bathwater, I'd want to see whether AMPK agonists like AICAR do in fact synergize with stresses like UV and peroxide to increase apoptotic cell death in the skin. If they do ... well, I think we found that catch."

Link: http://ouroboros.wordpress.com/2008/09/22/amp-activated-kinase-the-target-of-exercise-mimetics-may-contribute-to-photoaging-and-cell-death/