Cycling in your 40s: The Muscle Decade

Because nerve stimulation to the muscles—which makes them contract—weakens around now, your muscle mass can take a hit once you reach middle age; some estimates put the average loss at a third of a pound per year. Hormonal changes don’t help. It happens more quickly in fast-twitch fibers (the kind you might use to contest a town-line sprint), which affects the body’s ability to generate power. Some experts estimate that you can lose 20 percent of your power per decade and 10 percent of your strength. “While it’s a slow decline in men,” says exercise physiologist Stacy Sims, PhD, “there’s a more marked drop-off in women.” Your muscles also lose their capacity to use fuel as efficiently—another reason that peak power decreases—and to clear out lactate. The upside? Slow-twitch fibers (the ones you use for sustained efforts) start to dominate, and some studies show that aerobic capacity can remain virtually unchanged. “It helps explain the endurance capabilities of some older riders,” says Scott Morrison, an athletic trainer at the University of Pittsburgh Medical Center Cycling Performance program.