One of the benefits of aerobic exercise is that with consistent training, you can increase your aerobic fitness level. What does this mean? When you’re aerobically fit, you have a greater ability to sustain exercise at a submaximal intensity. In other words, you have more endurance. That comes in handy if you’re running a 10K or a half-marathon where you must sustain exercise for a longer period of time. The additional stamina you get from being aerobically fit comes in handy too.
Improvement in aerobic fitness is partially due to an improved ability to deliver oxygen to muscle cells and tissues during exercise. First, you breathe in oxygen; it enters the bloodstream, and your heart pumps the oxygenated blood throughout your body, including your muscles. During exercise, your heart has to work harder to deliver oxygen than it does at rest because your muscle cells demand more oxygen to make ATP, the energy currency they use for muscle contraction. Once you stop exercising and recover, the demand for energy and, in turn, oxygen falls back to baseline.
Therefore, it is not surprising that aerobic exercise training forces your heart to adapt and become a more efficient pump. To meet the increased demand for oxygen during exercise, your heart has to increase the amount of blood and oxygen it delivers per unit of time. At rest, skeletal muscles receive only about 20% of the blood and oxygen the heart pumps to the body. However, during maximal exercise, the percentage rises to almost 80%. That’s a big increase in demand! To deliver this much blood and oxygen, your heart rate has to increase.
If you keep training consistently, your heart will gradually adapt to the increased demand for oxygen delivery by becoming a more efficient pump. In response to the greater demand for oxygen, the muscular wall of the heart increases in size so that your heart can pump with more force. As a result, it can pump out more oxygenated blood with each beat. This increase in stroke volume means the heart doesn’t have to beat as many times per minute to deliver the same amount of oxygen. It also becomes a more efficient pump at rest. That’s why endurance athletes often have a slower heart rate than the average population. Their hearts are more efficient both during exercise and at rest due to their training.
Not only does your heart become a more effective pump in response to aerobic training, but your muscles also become more proficient at pulling the oxygen from the blood as the heart delivers it. The muscles pull the oxygen molecules into the muscle cells with greater ease. So, another adaptation to aerobic training happens at the level of the muscle. The muscle cells, too, become more efficient at getting the oxygen they need.
But that’s not the end of the story. Aerobic training changes what happens inside muscle cells too. To make the energy to fuel exercise, the mitochondria is where the action is. It’s the mitochondria that make ATP to fuel exercise with the help of oxygen. A slow-twitch muscle fiber has up to 19% of its volume occupied by mitochondria in highly trained individuals. That’s because they need large amounts of oxygen and fuel to sustain their workouts, and slow-twitch muscle fibers are the ones optimized for endurance exercise. So, it makes sense that the greatest number of energy-producing mitochondria would be located in these fibers.
In contrast, a person who’s less active will only have 5-12% mitochondria. Therefore, another adaptation to aerobic exercise is an increase in the number of mitochondria inside slow-twitch muscle fibers. Boosting the number of mitochondria means more “production plants” to make ATP to fuel aerobic or endurance exercise. Also, each mitochondrion becomes more efficient. The enzymes mitochondria use to make ATP increase in number.
How Much Can You Improve Your Aerobic Fitness?
Now, that you know how adaptations to aerobic exercise take place, how much can you improve aerobic fitness? Research suggests the average person can improve V02 max, a measure of aerobic fitness, by around 20% through training. However, there is a small percentage of people who show little or no improvement in aerobic fitness even with proper training. However, most people will show some improvement after 6-8 weeks of aerobic training.
Is Age a Factor?
Now to the big question. Are younger people able to make greater improvements in aerobic fitness in response to training than older folks? Aerobic capacity declines with age at a rate of about 20% to 25% per decade in healthy people over the age of 70. However, older people who are physically active start with a higher baseline aerobic capacity. Research shows that older men and women can boost their aerobic fitness by the same percentage as younger people. However, the level at what the adaptations mainly take place (heart, muscles, or mitochondria) may differ in younger women and older women. Studies show that younger people and men enjoy greater improvements in the heart’s ability to deliver oxygen to muscle cells than do older women. In contrast, older women make greater gains at the level of the muscle with an increased ability of muscle cells to grab on to oxygen. However, both improve aerobic fitness, just in different ways.
What’s encouraging is that research shows you can boost your aerobic fitness at any age. That’s important since not meeting the recommended guidelines for physical activity (150 minutes of moderate-intensity exercise per week or 75 minutes of vigorous activity weekly) is linked with a greater risk of high blood pressure, coronary artery disease, type 2 diabetes, obesity, and osteoporosis. Regular physical activity is also correlated with a lower risk of some forms of cancer. Studies even show that older people with cardiovascular disease can improve their aerobic fitness level through aerobic training, although it’s important to do it under supervision.
The Bottom Line
Older adults can improve their aerobic fitness by about the same percentage as a younger person. However, they’ll start out at a lower baseline due to the natural age-related loss of aerobic capacity. Still, it’s never too late to make improvements. That’s the power of exercise!
References:
· Physiology of Sport and Exercise. Third edition. Wilmore and Costill. 2005.
· Circulation. 2018;137: 1549–1560.
· Can Fam Physician. 2010 May; 56(5): e191–e200.
· DiscoveryMedicine.com. “Aerobic Exercise in the Elderly: A Key to Successful Aging”
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What Role Does Aerobic Capacity Play in Successful Aging?
Why Does Aerobic Capacity Go Down as You Age?
How Much Can You Improve Your Aerobic Capacity?
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