VO2max: What It Is, and Whether We Should Worry About It

Fair warning, this article is going to be long and very scientifically technical, so continue at your own guaranteed enjoyment! Science!

The term VO2max has been circulating in the exercise physiology world since A.V. Hill coined the phrase in the 1920’s and has been a huge driver in endurance athletes for decade. VO2 is defined as the body’s maximal ability to consume oxygen, is one of the most commonly measured components to track training progress and is a good indicator of general aerobic fitness. In theory, the higher your intensity of exercise, the higher your VO2 would be. So generally speaking, a more trained athlete would have a VO2max higher than a lesser trained athlete. Throughout most of the past century, endurance athletes, especially runners, have been taught that VO2max is the best way to predict performance on race day, so lets take a look at how a runner, and even a non-runner wanting to increase upper end aerobic fitness, can train their VO2max.

VO2max is measured using the Fick Equation: VO2=Q(CaO2-CvO2), where Q is the cardiac output, CaO2 is the oxygen concentration in the arteries, and CvO2 is the concentration in the veins. Yes, I know, that’s a lot of symbols to look at, but in order to understand the science of training VO2max, you need to understand the components of this equation. By the properties of algebra, in order to increase VO2max, we can either increase cardiac output or increase the difference in O2 concentration from the arteries to veins.

First, lets look at cardiac output, which is the amount of blood the heart pumps out in a single minute (heart rate * stroke volume). We know that heart rate, at least its ceiling, is not something that we can train to increase. Or at least that is what scientific research has led us to believe at this time. Your body’s max heart rate is its max heart rate. End of story. In fact, your max heart rate is almost guaranteed to decrees as you age. So how can we train for higher cardiac output? Stroke volume (SV). One of the best ways to do this is to increase the strength of your heart, because its a trainable muscle just like your quad or your bicep. As your heart gets stronger, it is able to produce more force each time it contracts. The more force it contracts, the more blood it can expel into arteries. This is the same reason a trained athlete will generally have a lower resting heart rate than an untrained person. The heart is stronger in the athlete and therefore can get the same amount of blood circulated through the body with less heart contractions.

Next, lets look at increasing the a-vO2 concentrations. One way to do this is to increase the amount of O2 initially in the blood when it leaves the heart by increasing the number of hemoglobin, the blood’s oxygen transport vessels. If there is more O2 in the blood, there is more O2 to give away to the muscles. This is essentially how blood doping, which I am in no way advocating, works. Increase the hemoglobin concentration by injecting extra blood into the body. This would lead to explain why doped athletes (not to name names) have had a history of very, very, very high VO2max measurements. But this comes with a price, hence why blood doping, aside from being highly illegal for sport, is dangerous. Too high of a hemoglobin concentration makes the blood very thick, in turn making it harder for the blood to pump through the body, which can be very dangerous. But in the interest of getting back on track, the next way to increase the a-vO2 is to increase capillary density. Capillaries are the smallest of the arteries in the body that directly lead into the muscles. The more trained a muscle group is in an athlete, the higher the density of capillaries is. Why does this matter? The more capillaries an athlete has, the more blood can be sent to the muscles, and the more O2 the muscle can intake. Lastly, a-vO2 can be increased through increased utilization of O2 in the muscle. The best way to do this is through increased mitochondria size and intensity. Mitochondria are the structures in the muscle cells that use O2 to create ATP, or energy, so the bigger and more numerous the mitochondria are, the more O2 the muscles can absorb.

Now we know scientifically how an athlete can increase their VO2max, so its time to put it into practical terms in order to see how exactly we can induce these effects in training. Obviously, the stronger your heart, the more blood it can pump (higher stroke volume). The best way to strengthen your heart, just like every other muscle, is to work it past what is comfortable. Doing high intensity training in the form of intervals can push the heart into those higher intensities, following the progressive overload principals. That is the most effective way of training for increased VO2max. But we can also train our bodies to have higher capillary and mitochondria densities, which, as you remember from earlier, are both factors contributing to a higher a-vO2. Capillary density comes with aerobic and high intensity training because any time your muscles are used, they need blood. The more you use them, the more blood they need, and the human body is amazingly adaptable to this, leading to new capillaries being created. Mitochondrial density is created in much the same way. More exercise volume and higher intensities both increase the number of these structures in muscle cells, but long, continuous bouts of exercise have been shown to have the best results. For example, a 90 minute run has been shown to create more mitochondria than doing 2 45 minute runs in a day.

Now that we have a pretty good idea of what VO2max is and how we can train to raise it, lets take a look at the important question we are all sitting on the edge of our seats to hear. Does it matter? Big picture? To some degree, yes. If an untrained individual has a very low VO2max, it is likely going to be a performance predictor when compared to a trained runner that has a high VO2max. But when we start looking at trained runners, studies have shown that VO2max tends to not be a very good indicator of endurance performance. This leads to another question, why do we even bother? Simply put, its what people are used to. VO2max was the standard for endurance performance for decades because it was the only thing we knew how to test. The fact of the matter is that runners with the same VO2max can have a very wide range of performance results. This is because VO2max isn’t the one and only limiter in performance. Muscular endurance, will power, and several other factors can contribute to when an athlete hits the breaking point. A single example of this is a study that was done on female world record 10K and marathon holder Paula Radcliffe by Andy Jones. At the beginning of the study, Radcliffe was running 25-35 miles/week with a VO2max around 72. At the conclusion, she was running 120-160 miles/week and had not changed her VO2max. Most importantly, her performance had substantially increased. While this is just one example, its a very good one and similar studies have been replicated.

So to wrap things up, VO2max is defined as the body’s maximal ability to consume oxygen and has for years been seen as synonymous with endurance performance. Through specific types of training, we can train ourselves to have higher VO2max ceilings. Even though for decades, VO2max has been seen as the performance standard in endurance athletes, seeing multitudes of training plans build around it, recent research has shown that it is not the only factor. In fact, it really is a pretty poor indicator of endurance performance, especially among trained athletes. Hopefully, as more research is done on the topic, the nature of training and coaching will start to shift away from only worrying about VO2max and we can start to see better, more consistent results in our racing!