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What’s Your Real VO2 Max Number?

  • By Matt Fitzgerald
  • Published Mar. 12, 2014
In a standard VO2 max test, subjects run on a treadmill at increasing speed until they're unable to continue. Photo: www.shutterstock.com

An alternative VO2 max test protocol is more like a real race.

A few years ago I finally got around to taking my first VO2 max test. Actually, it wasn’t a VO2 max test primarily; it was aimed at testing my running stride mechanics.

The VO2 element of the test followed a standard protocol. I started off running at a very easy pace on a treadmill. After three minutes the belt speed was increased to a moderate pace. After another three minutes the belt speed was increased again. This continued until I deemed myself completely exhausted and stepped off the treadmill.

There are some well-known and long-lamented limitations of this protocol. The thing people complain about most is that the standard VO2 max test protocol does not resemble how people exercise in the real world. In a running race, you cover a fixed, predetermined distance as quickly as possible. This is known as a closed-loop task. By contrast, in a standard VO2 max test, you are left to somewhat arbitrarily quit when you feel you’ve had enough. That’s an open-loop task.

The practical implications of the difference between closed and open loops are quite large. For example, the scientist at Eastern Michigan University who tested me, Stephen McGregor, is using fancy three-dimensional accelerometers to determine how the running stride changes as fatigue sets in. But fatigue manifests in very different ways in closed-loop and open-loop tasks.

In a closed-loop task, a runner freely adjusts his pace throughout the task to ensure that “exhaustion” is reached at the finish point and no sooner. If he is too aggressive, he may slow involuntarily toward the end. But more likely, he will hold back slightly more than necessary and find himself able to sprint to the finish.

In an open-loop task, however, there is no freedom besides the freedom to quit whenever you feel exhausted. The pace is dictated and held fixed at each stage. Therefore testers are unable to study what happens, physiologically, or why it happens, when a runner slows down involuntarily or kicks to finish himself off at a predetermined endpoint.

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McGregor recognizes that there are undoubtedly important differences in the esoteric stride fatigue variables he looks at in open-loop versus closed-loop tasks, and he is eager to move his research away from the treadmill so he can learn more about fatigue in the real world.

In the meantime, two English Researchers, Lex Mauger and Nick Sculthorpe at the University of Bedfordshire, created a closed-loop VO2 max test in 2010 that probably should completely replace the old, open-loop test. The Mauger-Sculthorpe test is much more like a real race. It is a fixed 10 minutes in length and it is divided into five two-minute stages. The subject is given a certain perceived exertion target for each stage. I’m not sure exactly what the targets are, but they’re probably something like 8, 11, 14, 17, and 20 on the standard scale of 6-20, where 20 equals suffering as much as you can possibly suffer. Subjects are free to set their own pace to maintain the targeted exertion level at each stage.

Mauger and Sculthorpe got a surprising and unexpected result when they conducted a study to validate their new test protocol. Subjects were able to attain significantly higher VO2 max values in the new, closed-loop test than in the traditional, open-loop test. Why? They don’t know, but I have a guess. I think it’s simply easier to finish yourself off in a closed-loop task. When you see the finish line ahead and you know it’s not going to move, it’s not too difficult to feel your way toward the highest speed you can sustain until you reach it. An open-loop task is more like a moving finish line. You’re stuck at a fixed intensity that you cannot increase to finish yourself off. Instead, you have to decide when the task has finished you, in a sense.

I’m not sure if this is another way of saying the same thing, but I also believe that a closed-loop task is more motivating. Human beings are task-oriented by nature. We like to do the thing until it’s done. In the Mauger-Sculthorpe test you know where the end is before you start. The subject has a specific goal, and I think that motivates him to work harder. In the traditional test you are given only the prospect of ever-increasing misery until you raise a white flag of surrender.

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Human beings are quite willing to suffer, but we need a reason. In a race or other closed-loop task you have something to suffer for. In a traditional VO2 max test you really only suffer to suffer, and that’s simply unnatural.

Interestingly (I think), when I performed my VO2 max test I instinctively tried to turn it into a closed-loop task. Based on my knowledge of the protocol, I had some sense going into it of how long I would last. When I got to the stage that I figured would probably be my last, I looked at the elapsed time display and saw that it read 15:30 or thereabouts. I kept my eyes on this display as my suffering level increased.

When I got to 16:15, I set a goal to make it to 17:00. By 16:45 I was hurting as much as I ever do in any race, but I hung on until 17:00 precisely and then jumped off the treadmill. Without that time display in front of me I would have quit sooner.

Is that cheating?

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About The Author:

Matt Fitzgerald is the author of numerous books, including Racing Weight: How To Get Lean For Peak Performance (VeloPress, 2012). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt visit www.mattfitzgerald.org.

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