A new scientific statement from the American Heart Association argues that VO2 max, long used as a measure of running fitness, should be considered a “vital sign” by doctors.
That’s because low VO2 max is associated with higher risk of a long list of serious conditions, including heart disease, certain types of cancer, dementia, Alzheimer’s, depression, and Type 2 diabetes. In fact, it’s a better predictor or mortality risk than better-known risk factors like smoking and high blood pressure. You can read the full scientific statement here.
There are a few interesting aspects of this statement worth highlighting here.
U.S. Army/Cpl. William Smith 4th Inf. Div. PAO2 max shifts the focus from process (you should get more exercise) to outcome (you should be fitter). VO2 max, or cardiorespiratory fitness (CRF), as it’s referred to clinically, is your ability to take oxygen from the air and deliver it to your muscles for use.
At first glance, this may seem unfair, since research suggests that about half of the VO2 max differences between people are the result of genetic factors. But, as the authors of the scientific statement point out, that’s actually no different from other major risk factors like insulin levels, blood pressure, and blood sugar. We all get dealt different hands, and it can only be helpful to know what risks we face and how we might be able to minimize them.
How your VO2 max responds to exercise also varies from person to person—again, the genetic contribution is thought to be somewhere around 50 percent. Still not fair: some people will have to work considerably harder than others to maintain a healthy VO2 max. But isn’t it better to know if your exercise routine isn’t getting the job done, rather than assuming that since you’re doing a “typical” amount you should be okay?
Can Your Watch Estimate Your VO2 Max2 max? This is the part that caught my attention, since the paper argues that “routine estimation of CRF in clinical practice is no more difficult than measuring blood pressure.”
Really?! As someone who has done a few VO2 max tests, which involved progressively harder treadmill runs to complete exhaustion in sophisticated laboratories with breathing masks and tubes attached to me, this seemed surprising.
In fact, that method—exercise to exhaustion with direct measurement of gases inhaled and exhaled—is the gold standard for measuring VO2 max, but there are other ways of estimating it. In descending order of reliability:
(1) exercise to exhaustion with measurement of breathing gases;
(2) exercise to exhaustion, with estimate based on highest speed or distance achieved (e.g., 12-minute run);
(3) non-exhaustive exercise, with estimate based on the relationship between heart rate and work rate (e.g., 1-mile walk);
(4) no exercise, with estimate based on parameters like age, resting heart, and reported physical activity.
It’s that last one that is “no more difficult than measuring blood pressure,” though it’s considerably less accurate than the more demanding tests.
The researchers suggest that everyone should have their VO2 max estimated in this way (or, better yet, with a submaximal exercise test) once a year during their annual physical. And every once in a while (on a schedule not yet determined), everyone should have a true maximal VO2 exercise to exhaustion with measurement of breathing gases.
So, you ask, how do I estimate my VO2 max? Here’s one of the equations they suggest, developed from Norwegian data in Do Some People Not Respond to Exercise.
You’ll need to know your age (A), resting heart rate (HR), waist circumference (WC) in centimeters, and “physical activity index” (PA, more on that below).
For men, the VO2 max estimate (in units of ml/kg/min) is: 100.27 + 0.226 * PA – 0.296 * A – 0.369 * WC – 0.155 * HR.
For women, it’s: 74.74 + 0.198 * PA – 0.247 * A – 0.259 * WC – 0.114 * HR.
For example, I'm 41, with a waist circumference of around 31 inches (79 cm), a resting heart rate of around 45, and a physical activity index of 22.5. Plugging those numbers in gives me an estimated VO2 max of 57 ml/kg/min. It's a been a while since I've had a proper VO2 max test, but that's likely an underestimate of my actual VO2 max. I suspect equations like this will likely underestimate many endurance athletes whose VO2 max values have been raised by years of fairly rigorous training that isn't fully captured by the physical activity index—but still, it's a good ballpark estimate.
Some more details on the physical acitvity index: calculating it requires multiplying three numbers together.
The first number, frequency, is 0 if you exercise less than once a week; 1 if you exercise once a week; 2 for twice or three times a week; and 3 if you exercise almost every day.
The second number, intensity, is 0 if you take it easy; 5 if you push to heavy breath and sweat; and 10 if you push near exhaustion.
The third number, duration, is 1 if you typically exercise for 30 minutes or less; and 1.5 if you typically exercise for more than 30 minutes.
So I estimated mine multiplying 3 x 5 x 1.5 = 22.5. The 5 for intensity corresponds to "heavy breath and sweat," which describes my typical runs. That said, two or three times a week I do workouts where I push near exhaustion, so it might have been reasonable to use 10 rather than 5, for a total physical activity index of 45. Had I done that, my estimated VO2 max would have been 62 ml/kg/min—probably a better estimate, though still (I hope) a little below the actual value.
How should you interpret the resulting number? Well, according to the new statement, perhaps that’s something you should discuss with your doctor! Goal levels obviously depend on a variety of factors, more prominently age and sex.
One point the researchers emphasize is that the biggest gains in health come for people at the lowest end of the fitness spectrum who improve their VO2 max—so you don’t need to be a champion athlete to see benefits. One rough threshold is that the highest mortality risks are seen in those with VO2 max below about 18 ml/kg/min. Once you get above 35 ml/kg/min or so, you’re in a zone associated with longer survival.
That’s because low VO2 max, the best way to raise it is exercise—and broadly speaking, more and harder exercise produce bigger gains.
The real question, of course, is: Will knowing (or estimating) VO2 max be more effective at spurring people to exercise than whatever current prodding and nagging they get? I’d like to think the answer is yes, but in reality I’m far from sure. Understanding human motivation is turning out to be a problem that is far trickier than understanding VO2 max itself.
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