Understanding VO2 Max
Understanding VO2 max is essential if you want to improve your cardiovascular endurance. It can be a little complicated to understand, but I will explain VO2 max as simply as I can.
So what is VO2 max? It represents the maximal oxygen uptake or consumption of oxygen in one minute. The term peak VO2 means the same thing and is being used more often. Measuring VO2 max is an excellent tool to assess the function of several physiologic systems working together to deliver oxygen to the cells throughout the body. These systems include the lungs, heart, blood, and skeletal muscles.
How is VO2 Max Measured?
VO2 max testing is either performed while exercising on either a treadmill or bicycle ergometer using a number of different protocols. The individual breathes through a mask connected to an analyzer that measures how much oxygen is being breathed in and how much carbon dioxide is being breathed out. The individual is also hooked to a heart rate monitor. The test can be done with or without EKG tracings.
How VO2 Max is Useful
VO2 max is useful to determine:
- Pre-clinical signs of cardiac disease, lung disease, or metabolic disease.
- Athletic performance.
- The level of health versus disease.
- The potential to improve energy capacity (exercise training design).
What Determines VO2 Max?
There are three main determinants of VO2 max: heart rate, stroke volume, and something called a-vo2 difference (arterial-venous difference). Heart rate times stroke volume equals cardiac output. Cardiac output is the amount of blood the heart can pump per minute. During maximal or peak exercise cardiac output increases four to five-fold from rest.
Heart rate you understand. Stroke volume is the amount of blood the heart pumps from the left ventricle per heart beat. Stroke volume increases slightly during exercise and reaches a finite limit at 50% of VO2 max. Above that level HR is the main way that cardiac output increases.
As the intensity of the exercise picks up heart rate goes up. You probably have also noticed that the longer you exercise, even if you keep the same pace, your heart rate also increases. But, heart rate can only increase so much, too, and maximum heart rate for an individual is age related.
The arterial-venous difference is the difference in the amount of oxygen in the arteries and the amount of oxygen in the veins. Arteries carry blood (and oxygen) from the heart to the tissues. Veins carry blood back to the heart which then goes to the lungs to receive more oxygen. The a–v02 difference tells us how well muscles and tissue are extracting oxygen from the bloodstream. As we become more fit, tissues can extract more oxygen from the blood creating a greater a-v02 difference. At rest we extract only 25% of the available oxygen from the blood. During peak exercise we can extract 75% of the oxygen available in the blood.
VO2 max testing also measures the amount of air move through the lungs. At rest the average sedentary adult move 6 liters of air per minute. During peak exercise that increases 15 to 25 fold. That’s moving a lot of air. Training can increase that another 25%.
What’s a Good VO2 Max?
- 60-90 ml/kg/min for world-class male and female athletes
- 45-60 ml/kg/min for trained recreational athletes
- 28-44 ml/kg/min for sedentary “healthy” adults
- <25 ml/kg/min in patients with heart disease
Studies show that a greater risk reduction in heart disease can be achieved by achieving a VO2 max of 42-43 ml/kg/min than can be achieved by lowering cholesterol, quitting smoking, or adequate management of high blood pressure and diabetes. In other words, becoming more fit does more for heart disease prevention than modifying the other traditional risk factors for heart disease. This is why exercising is so important for health.
In a future post we will look at how data obtained from VO2 max testing can be used to design an exercise program to improve energy capacity enabling you to get to that magic VO2 max level of 42-43 ml/kg/min.
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