Why Does Aerobic Capacity Go Down as You Age?

Why Does Aerobic Capacity Go Down as You Age?

(Last Updated On: March 25, 2019)

Why Does Aerobic Capacity Go Down as You Age?

If you’re in your 60s, you probably don’t have the aerobic capacity you did when you were in your 20s. Aerobic capacity also referred to as V02 max, is your body’s maximum ability to take up and use oxygen. During exercise, your muscle cells need a steady supply of oxygen to make ATP, the energy source muscles need to contract.

Although your muscles can make ATP without oxygen for short periods of time, the amount of time you can sustain exercise without oxygen is limited. As oxygen delivery slows, you get that old, familiar burning as lactic acid and hydrogen ions build up and you feel the overwhelming urge to stop. Simply put, the more oxygen you can get to your muscles, the longer you can sustain exercise.

Unfortunately, V02 max goes down with age. Curious as to what your aerobic capacity is? You can actually measure your V02 max, not at home, but in a fitness facility that offers this type of testing. To do this, you would run on a treadmill or pedal an exercise bike as the testers gradually increase the intensity. Throughout the session, you wear a mask over your nose and mouth to measure how much oxygen and carbon dioxide you take in and breathe out.

At some point, as you approach exhaustion, the amount of oxygen you take in will no longer continue to rise. The testers will document peak oxygen uptake in units of milliliters of oxygen. To get your V02 max, they would divide this value by your body weight in kilograms. There you have it – your V02 max.

If you were to measure your V02 max over time, assuming you don’t do any type of aerobic training to skew the value, it would decline every decade. Previously, it was thought the decline was linear, between 5% and 9% every 10 years. But more recent research shows the decline is nonlinear. Rather the decrease in V02 max is 3% to 6% during the third and fourth decades of life but accelerates after the age of 70 to as high as a 20% reduction every decade thereafter. This holds true even when you take into account changes in body weight with age.

What accounts for this transformation? The most significant change that happens is the amount of blood your heart can pump with each beat, referred to as the stroke volume, goes down. Your heart becomes a less efficient pump. When your heart pumps less proficiently, it can’t deliver oxygen to your muscles during exercise as quickly.  Along with it, your maximum heart rate declines. You might wonder why this happens. For one, the cells that initiate each heartbeat called pacemaker cells become less responsive to stimuli like exercise and stress.

When you exercise or place your heart under any type of stress, your adrenal glands release chemicals called catecholamines. These chemicals increase your heart rate for greater oxygen delivery to your tissues during times of need. As you age, your heart becomes less sensitive to these chemicals and doesn’t respond as readily to the influence of catecholamines. With age, especially if you have high blood pressure, your arteries and the chambers of your heart become stiffer, meaning they don’t fill with as much blood and are less efficient at pumping blood and oxygen to tissues.

As you can see, part of the reason you lose aerobic capacity with age is due to changes in how well your heart and blood vessels pump oxygen – but that’s not the only reason. Inside your muscle cells are organelles called mitochondria. These tiny “power factories” have the important job of making the ATP your cells need for muscle contractions and for other activities as well.

As it turns out, mitochondria age too. Every time your mitochondria ramp up to produce ATP, it creates damaging free radicals that, unfortunately, injure the mitochondria themselves. Not only does this reduce aerobic capacity – research also suggests this decline in mitochondrial function partially explains why people become more insulin resistant with age. That’s why there’s so much focus on eating an antioxidant-rich diet. Antioxidants may help protect against mitochondrial damage.

Preserving Aerobic Capacity Due to Aging

All humans lose aerobic capacity with age, but if you maximize your aerobic capacity through exercise, you’re starting from a higher baseline. As a result, some aerobically fit 50-year-olds have greater exercise capacity than sedentary 20-year-olds. In terms of maximizing aerobic capacity, vigorous exercise appears to be better than low to moderate-intensity exercise – think HIIT training.

Aerobic training increases stroke volume and your heart’s ability to deliver blood and oxygen AND increases the number of mitochondria inside muscle cells, so you have more “factories” to produce the energy you need to fuel exercise. Exercising vigorously may also significantly slow the loss of aerobic capacity that happens with age.  In one study, older athletes who did high-intensity cardiovascular exercise lost aerobic capacity at only half the rate. Even more exciting is the fact that a few studies show Master athletes who continue to train at a very high level are able to maintain their aerobic capacity.

The Bottom Line

If you’re sedentary, you’ll lose your aerobic capacity at a fairly rapid rate, especially after the age of 70. The good news? Vigorous exercise can greatly slow this loss and there’s some evidence suggesting that training at very high levels can preserve aerobic capacity. Another point to remember – body composition matters. You lose muscle mass with age, further reducing strength and aerobic performance. Keep up the intensity of your aerobic AND strength-training workouts so you can stay as fit as possible as you age.

 

References:

Appl. Physiol. Nutr. Metab. 2008 Feb: 33(1): 130-40.

PNAS. “Decline in skeletal muscle mitochondrial function with aging in humans”

Circulation. 2005; 112: 624-626.

J Physiol 586(1):55-63.

The Physiological Factors Limiting Endurance Exercise Capacity. Len Kravitz, Ph.D and Lance C. Dalleck, M.S.

Journal of Applied Physiology, vol 51(3), pp 634-640, 1981.

Sports Performance Bulletin “VO2 Max: can veteran athletes prevent a decline in aerobic capacity?”

 

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What Role Does Aerobic Capacity Play in Successful Aging?

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How Aerobically Fit Are You? Here’s a Simple Way to Find Out

 

 

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