Physiology: Endurance Improves As You Age

I got this article from a road bike newsletter I receive. It comes from issue number 337.

The article describes why older people seem to get better in long endurance sports than younger. For example, many of the ultra-marathon winners are over 40 or 50. See the Badwater Ultamarathon, where the average participant was 47.

This is a good review of muscular physiology. Older people show more endurance, because they lose nervous innervation of fast twitch muscle fibers.

ED'S NOTE: I just heard from an excited Gabe Mirkin, M.D. He often rides more than 200 miles a week. He's 74 years old. So the news he sent to RBR is vitally encouraging to him and, I suspect, will be heartening to you too.

Here's Dr. Mirkin's message:

"I have noticed that younger riders can easily pull away from me in short bursts, but I keep coming back on them and seem to be better able to keep up with their accelerations as the ride progresses.

"The January 2009 issue of Exercise and Sports Sciences Reviews investigates the entire world's literature to show that endurance improves as you age. Wow!

"Maximal muscle contraction force occurs when you do a single muscle contraction with all your might. Even though older people are not as strong as younger ones, many studies show that they can retain maximal force after many contractions far longer than younger people can.

"Here's the theory and evidence to explain why aging improves endurance:

"Muscles are made up of millions of individual fibers just as a rope is made up of many different threads. Each muscle fiber is enervated by a single nerve. As you age, you lose nerves throughout your body. And when you lose the nerve that enervates a specific muscle fiber, you also lose that fiber.

"Muscle fibers are classified as type I endurance fibers [also called slow twitch] and type II strength and speed fibers [fast twitch]. With aging, you lose far more nerves that enervate the strength and speed fibers than those that enervate the endurance ones.

"So, with aging, you lose strength but you retain a greater proportion of endurance fibers.

"Muscle fatigue comes from the accumulation of waste products that occurs while food is converted to energy to power muscles. With the same percentage of their maximal muscle force, older people accumulate far lower levels of these end products than younger people do. Therefore, even though older people are relatively weaker, they can maintain their forceful contractions far longer and they have greater endurance.

"This exciting recent data will encourage me to train even harder."