By Uphill Athlete co-founder Scott Johnston
Max VO2 is the Holy Grail of endurance qualities, right? Looking at the fitness landscape, you’d sure think so. Many training methodologies embrace it as the metric that rules all others, and the popular media fuels this misunderstanding with articles about how to boost your max VO2 in order to be the best athletic you. But of the three main components that pertain to endurance—economy, speed at lactate threshold (aka anaerobic threshold), and max VO2—max VO2 correlates the least with performance.
During my ski racing career, in which I was a World Cup also-ran, I was tested several times for max VO2. I always tested with a higher max VO2 than the other US Ski Team guys I raced against who routinely placed in the top ten and occasionally even in the top five in World Cup races. That’s when I began to question the validity of the assumption that max VO2 is a predictor of performance, and I sensed that something else was holding me back. Years later, I pinpointed that weakness: economy, especially at racing speeds; it’s a metric that didn’t even figure into training 35 years ago.
At this point my long-burning questions about max VO2 turned into full-blown skepticism of the models that place this quality on a pedestal above all others—and often to the detriment of others.
I have personally trained athletes with low max VO2 values who have been quite successful at the World Cup level. Before I worked with him, one of these skiers had been the recipient of huge financial and material resources from the US Ski Team over the course of five years, years that were devoted almost exclusively to improving his max VO2 at the expense of other aspects of his training. He did max VO2–protocol interval sessions three times a week, and his max VO2 was tested three or four times a year. The net effect of this myopic approach was essentially zilch. There was no change in his vaunted max VO2 value, and his race performance stagnated. He lost his spot on the team.
He was 30 when he came to me for training, and I told him it was fruitless at this late stage to attempt to change his max VO2. “You’ve been a professional athlete for most of your life now,” I said. “You’re stuck with what you’ve got.” But it didn’t matter that we couldn’t supercharge his engine; instead, we worked on his economy so that it would cost him less energy to go at race pace. The next year, he was the fastest guy in the country. He went from being kicked off the team to winning major races.
A common definition of insanity is doing the same thing over and over while expecting different results. All it took to change the game for this skier was shifting the focus of his training.
A scientist named A.V. Hill was the first to figure out that work limitation is oxygen related. Back in the early 1920s, Hill ran around a grassy field with a big balloon—a Douglas bag—to collect his exhaled air. Then he sampled the bag’s CO2 content to determine how much oxygen he used in the time he was running. He observed that as he increased intensity, his oxygen uptake would plateau. This was his max VO2—his max rate of oxygen consumption.
Hill’s discovery offered the first verifiable explanation for the limits of human performance, and it stuck.
A high max VO2 is an undoubtedly valuable tool to have in your arsenal of endurance qualities; successful endurance athletes often have very high max VO2 values. The problem is confusing cause and effect. Current popular understanding embraces max VO2 as the metric that governs and limits performance. But I believe that in reality max VO2 is the effect of performance, not the cause.
Many lab studies of training protocols use max VO2 as the measure of their success or failure. (1) It’s a relatively straightforward metric to isolate, obtain, and manipulate, and the tests are often easily repeated. A common study might involve a group of subjects who follow a certain training protocol for six to eight weeks; the change in their max VO2 from week one to the final week “determines” if the protocol works. If max VO2 goes up, it’s a success! The program improves max VO2.
But what does that actually mean? Among the untrained and young people, max VO2 is likely to increase rapidly regardless of the training protocol. It’s what is called a “first-wave response”: if you take someone who is not very fit and give them exercise, max VO2 is one of the very first things to go up. After about four months, however, it plateaus then responds much less significantly to training stimuli.
The heart muscle is super trainable—but not infinitely so. If you do a bunch of high-intensity interval training (HIIT) at or near max VO2, the heart muscle will respond by getting bigger and stronger: it ejects more blood, which gives you more cardiac output, which means more oxygen going to the muscles to power more work. But the heart muscle is surrounded by a sheath of fascia called the pericardium, beyond which it can’t grow. Once the heart reaches this point where it can’t get any bigger, max VO2 levels off. And if you overdo it with the HIIT, which is most effective for improving max VO2 in the short term, your max VO2 will eventually go down.
Several long-term longitudinal studies(1) of elite endurance athletes have shown that max VO2 values don’t rise at all—and in some cases decline—despite the athletes’ showing improved performances. During a taper phase in preparation for a big race, max VO2 typically drops due to the reduced training volume, but performance increases despite the drop.
Max VO2 is clearly not a neat-and-tidy measure of endurance, so why does the general exercising public continue to mistakenly embrace it as just that? Look no further than zingy headlines that equate boosting your max VO2 with guaranteed performance returns—headlines that over-inflate the importance of this single number and distort the bigger endurance picture.
Here’s the reality, especially as it pertains to the people we coach at Uphill Athlete: You do not need a monster motor to summit a Himalayan peak or run an ultra. No one races 50 miles or climbs a mountain while operating at their maximum capacity; you can only hold that effort for a few minutes. Besides, there’s so little oxygen at high altitudes that it’s physically impossible to operate anywhere near your top-end intensity. These pursuits demand endurance, which is the ability to sustain a sub-maximal workload for a long time—over multiple hours or even days. You’re not going to be running five-minute miles at 8,000 meters.
Max VO2 is just one of several things that goes into accounting for endurance: it might set your upper limit, but it doesn’t have much to do with how you perform at a sub-maximal level. So instead of getting all bent out of shape over your low max VO2, focus instead on optimizing your aerobic base. When it comes to long-duration events, that is the capacity what will make or break you.