What the Heck Is VO2 Max?

When sorting through the features of the latest generation of fitness devices, runners might pause and ask, "Do I need that?" I wondered just that myself this fall, when I noticed that a number of fitness trackers, including the new Microsoft Band, started including VO2 max as a metric.

Fitness devices are intended to improve our health and training performance by giving us useful information such as how fast our hearts are beating and how many calories we burn. But much of this information is only marginally helpful in shaping how we train. For example, although most of us understand the concept of calories, many of us don't eat solely to replenish the calories we burn in a workout. We may feel better about ourselves if we work off some of what we've eaten, but we don't necessarily stop gulping the sugary morning coffee drink after seeing how many calories we've burned.

VO2 max has been used for many years in assessing the aerobic capability of athletes. The test measures the maximum amount of oxygen that an athlete consumes during exercise. Think about the efficiency of a car and the size of its motor. (However, keep in mind that VO2 max is not a measure like maximum horsepower or torque that calculates the engine's ability to produce raw power.) Rather, VO2 max measures oxygen consumption, which is used in aerobic exercises like distance running. It doesn't tell us much about our power during anaerobic exercises like a running sprint. So, while VO2 max gives us a picture of the power of our "engines," it's not telling us how fast we would be "off the line."

To test VO2 max, athletes typically hook up to an apparatus that measures how much oxygen they breathe and how much oxygen and carbon dioxide they exhale during exercise. This is a direct measurement of how much oxygen is going in and how much is actually being used when athletes run. VO2 max is reached when oxygen consumption stops rising -- even when the workout gets harder. The measurement is helpful because it allows athletes to determine how intense their training should be -- and to monitor their VO2 max over time.

But does VO2 max deserve a place on fitness trackers? The first thing to consider is that such devices only estimate VO2 max by looking at a combination of heart rate and speed -- not by directly measuring oxygen consumption through gas exhalation.

Next, consider why you want it. While most device manufacturers say you can use your VO2 max estimate to predict race results -- Garmin's Forerunner 620, for example, will use it to estimate your 5K, 10K, half marathon and marathon times -- keep in mind that race result predictions assume you have the appropriate training to continue running over the length of the race. So, while an estimate might be spot on in estimating your 5K time, you will still run out of gas running a marathon you haven't trained for -- even if you pace it correctly based on that VO2 max estimate.

For most runners, it's more helpful to time yourself running 1,500 meters or 1 mile on a track. From this result, you'll be able to directly calculate your speed over a given distance. Running coaches call this metric VDOT, or "effective VO2 max," which is extremely useful in calculating all kinds of training information, such as the correct paces for intervals, tempo runs and even long-distance training. All you need to make this measurement is a stopwatch, an accurately measured running track and access to an online VDOT calculator.

The bottom line? VO2 max is an additional piece of data, but perhaps not one that will yield a great deal of value for many runners. Other than checking your progress over time or comparing yourself to other athletes, I don't see VO2 max guiding your training in many meaningful respects. As always, look for the fitness device that best fits your needs and budget -- but don't get swept up in features that may not be all that helpful to you as a runner.