Greater Endurance with Aging

I’m 74 years old and ride my bicycle more than 200 miles per week, often in pace lines with younger riders. 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 latest issue of Exercise and Sports Sciences Reviews (January, 2009) reviews the entire world’s literature to show that endurance improves as you age. Wow!

The 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 fiber, you also lose that muscle fiber.

Muscle fibers are classified as type I endurance fibers and type II strength and speed fibers. 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 your muscles. Scientists can measure fatigue by measuring the accumulation of acid (H+), Phosphate (Pi) and protonated phosphate (H2PO4) in muscle. 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 weaker, they can maintain their forceful contractions far longer than younger people can and they have greater endurance. This exciting recent data will encourage me to train even harder.
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