Intense exercise greatly increases your body’s need for oxygen. Hardly a surprise! To meet that need, your heart rate goes up and the amount of blood pumped with each heart beat increases to send more oxygen to your muscles. In addition, blood vessels leading to these muscles open wider to let more blood flow reach your hardworking muscles. Blood flow increases to the surface of your skin too, so you can more effectively eliminate heat by sweating. At the same time, parts of your body that don’t need extra blood and oxygen, such as your digestive tract, receive less blood flow. Blood flow is redistributed so that more blood goes to where it’s needed most during exercise – your muscles.
What about your lungs? What role do they play in meeting the demands of exercise? As you might have guessed, your breathing rate goes up as exercise intensity increases, so you can supply more oxygen to your lungs. In turn, this oxygen attaches to red blood vessels inside your blood vessels so it can travel from your lungs to your muscles. You also breathe more deeply as your body’s oxygen requirements rise during exercise. During intense exercise, your lungs move in and out as much as 150 liters of air, compared to only 6 liters at rest. As a result, your respiratory muscles have to work harder and contract with more force to take in more air with each breath.
Differences in Aerobic Capacity: Men versus Women
On average, men have a higher V02 max, a measure of aerobic capacity, than women. This is partially because men have more muscle mass than women. Heart size is correlated with the amount of lean body mass a person has, so men, on average, have a larger heart relative to women. This gives men an endurance advantage since a larger heart can pump more blood with each heartbeat relative to a smaller one. Assuming it’s a healthy heart, a larger heart is simply a better pump. How much of an aerobic advantage does this give males? Absolute V02 max values are 40 to 60% higher in men versus women, but when you consider relative values for V02 max, taking into account differences in muscle mass, differences in aerobic capacity are not as pronounced.
According to a new study, the energy demands of breathing during exercise are greater in women than they are in men. Could this partially explain why women have a lower aerobic capacity, on average than men? In a study published in the Journal of Physiology, researchers measured how much oxygen men and women consumed at different exercise intensities, including maximal and sub-maximal exercise as well as at rest. What they found was women required more energy to fuel their respiratory muscles during exercise than men because their respiratory muscles work harder during exercise. This means women may have to direct more blood flow to their lungs relative to a man. With more blood being directed to the lungs, less is available for exercising muscles to use. This could lead to earlier fatigue.
In addition, women have a smaller lung capacity than men. In fact, lung capacity in women, on average, is 30% less than a man’s. This difference may partially explain why a female’s respiratory muscles have to work harder to deliver oxygen to muscles and other tissues during exercise. Females take in less oxygen with each inhalation because of their lower lung capacity. As a result, women have to breathe faster to compensate and their lungs and respiratory muscles have to work harder.
Respiratory muscles work especially hard during pregnancy. During pregnancy, most women notice a decrease in exercise endurance and find that endurance exercise feels harder. This is due to the enlarged uterus pushing up on the diaphragm, thereby reducing lung expansion. As a result, a pregnant woman’s respiratory muscles have to work extra hard. Plus, women who are pregnant have increased oxygen requirements because they have to supply oxygen to the fetus too. As a result, exercise performance suffers.
Aerobic exercise performance decreases by as much as 50% by the sixth month of pregnancy. This doesn’t mean that you shouldn’t exercise during pregnancy, quite the contrary. Exercise can actually improve pregnancy outcomes, but it’s important to check with your doctor before taking part in vigorous exercise if you’re pregnant.
Lungs and Respiratory Muscles: Do They Limit Exercise Performance?
Previously, most research has failed to show respiratory function limits exercise performance, except at the most elite levels or in cases of lung disease or damage. Instead, most people are limited by the ability of their heart to deliver oxygen to tissues quickly enough during exercise and the ability of muscles to take up that oxygen fast enough to fuel high-intensity exercise. This new study suggests that respiratory fatigue MAY limit exercise performance, at least to some degree, in women. Females have a higher metabolic cost of breathing and have to supply more blood and oxygen to their respiratory muscles during exercise, making less available for exercising muscles. Of course, more research is needed to confirm this.
Can You Improve Respiratory Function During Exercise Through Training?
Some experts believe you can train your respiratory muscles to become stronger and this may improve exercise performance. One method used is called threshold loading. This technique involves breathing against resistance for a short period of time to help strengthen the respiratory muscles. Various devices are available that help do this. Threshold loading would theoretically reduce how quickly respiratory muscles fatigue by making them stronger and more efficient. This efficiency could reduce the amount of blood flow the respiratory muscles need to do their job and more blood flow can be directed to the working muscles. Whether or not this holds true in practice still isn’t clear. Most likely this type of respiratory training would only lead to small improvements in exercise performance.
The Bottom Line?
Traditionally, respiratory function wasn’t thought to be a limiting factor in endurance performance, except for people who smoke or have lung disease. This study suggests it may impact endurance performance in women, but it’s still questionable whether you can overcome that disadvantage by strengthening your respiratory muscles through techniques like threshold loading.
References:
“Oxygen cost of exercise hyperpnoea is greater in women compared with men.” The Journal of Physiology, 2015; DOI: 10.1113/jphysiol.2014.285965.
“Specific respiratory muscle training for athletic performance” Issue: Volume 27 Number 4.
Am Fam Physician. 1998 Apr 15;57(8):1846-1852.
American Pregnancy Association. “Effects of Exercise on Pregnancy”
WebMD. “Exercise During Pregnancy: Myth vs. Fact”
Medscape.com. “Why Doesn’t Exercise Grow Lungs When Other Factors Do?”
Sports Coach. “Specific Respiratory Muscle Training for Athletic Performance”
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