This research is being conducted to determine how oxygen extraction within exercising muscles is altered in younger and older women when beta-1 receptors (receptors that contribute to the rise in heart rate with exercise) are temporarily blocked through a medication infused into an arm vein. The findings will help us understand how aging affects the regulation of oxygen supply to working muscles is regulated with normal aging.

There will be 3 in person visits. Visit 1) Subjects will undergo a physical and one blood draw in the Clinical Research Center and then perform two recumbent cycling exercise trials on a stationary bike. Visit 2) Subjects will undergo a DXA scan and then perform two recumbent cycling exercise trials. Visit 3) Subjects will have an IV catheter inserted into an arm vein. They will then perform two recumbent cycling exercise trials. During one trial the will receive esmolol via the IV catheter and during the other they will receive saline via the IV catheter (random order).

$150