How Old Are You? Stand on One Leg and I’ll Tell You

This transcript has been edited for clarity. 
Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I’m Dr F. Perry Wilson of the Yale School of Medicine.
So I was lying in bed the other night, trying to read my phone, and started complaining to my wife about how my vision keeps getting worse, and then how stiff I feel when I wake up in the morning, and how a recent injury is taking too long to heal, and she said, “Well, yeah. You’re 44. That’s when things start to head downhill.”
And I was like, “Forty-four? That seems very specific. I thought 50 was what people complain about.” And she said, “No, it’s a thing — 44 years old and 60 years old. There’s a drop-off there.”
And you know what? She was right.
A study, “Nonlinear Dynamics of Multi-omics Profiles During Human Aging,” published in Nature Aging in August 2024, analyzed a ton of proteins and metabolites in people of various ages and found, when you put it all together, that there are some big changes in body chemistry over time — and those changes peak at age 44 and age 60. I should know better than to doubt my brilliant spouse.
But deep down, I believe the cliché that age is just a number. I don’t particularly care about being 44, or turning 50 or 60. I care about how my body and brain are aging. If I can be a happy, healthy, 80-year-old in full command of my faculties, I would consider that a major win no matter what the calendar says.
So I’m always interested in ways to quantify how my body is aging, independent of how many birthdays I have passed. And, according to a new study, there’s actually a really easy way to do this: Just stand on one leg.
The surprising results come from “Age-Related Changes in Gait, Balance, and Strength Parameters: A Cross-sectional Study,” appearing in PLOS One, which analyzed 40 individuals — half under age 65 and half over age 65 — across a variety of domains of strength, balance, and gait. The conceit of the study? We all know that things like strength and balance worsen over time, but what worsens fastest? What might be the best metric to tell us how our bodies are aging?
To that end, you have a variety of correlations between various metrics and calendar age.
As age increases, grip strength goes down. Men (inexplicably in pink) have higher grip strength overall, and women (confusingly in blue) lower. Somewhat less strong correlations were seen for knee strength.
What about balance?
To assess this, the researchers had the participants stand on a pressure plate. In one scenario, they did this with eyes open, and the next with eyes closed. They then measured how much the pressure varied around the center of the individual on the plate — basically, how much the person swayed while they were standing there.
Sway increased as age increased. Sway increased a bit more with eyes closed than with eyes open.
But the strongest correlation between any of these metrics and age was a simple one: How long can you stand on one leg?
Particularly for the nondominant leg, what you see here is a pretty dramatic drop-off in balance time around age 65, with younger people able to do 10 seconds with ease and some older people barely being able to make it to 2. 
Of course, I had to try this for myself. And as I was standing around on one leg, it became clear to me exactly why this might be a good metric. It really integrates balance and strength in a way that the other tests don’t: balance, clearly, since you have to stay vertical over a relatively small base; but strength as well, because, well, one leg is holding up all the rest of you. You do feel it after a while.
So this metric passes the smell test to me, at least as a potential proxy for age-related physical decline.
But I should be careful to note that this was a cross-sectional study; the researchers looked at various people who were all different ages, not the same people over time to watch how these things change as they aged.
Also, the use of the correlation coefficient in graphs like this implies a certain linear relationship between age and standing-on-one-foot time. The raw data — the points on this graph — don’t appear that linear to me. As I mentioned above, it seems like there might be a bit of a sharp drop-off somewhere in the mid-60s. That means that we may not be able to use this as a sensitive test for aging that slowly changes as your body gets older. It might be that you’re able to essentially stand on one leg as long as you want until, one day, you can’t. That gives us less warning and less to act on.
And finally, we don’t know that changing this metric will change your health for the better. I’m sure a good physiatrist or physical therapist could design some exercises to increase any of our standing-on-one leg times. And no doubt, with practice, you could get your numbers way up. But that doesn’t necessarily mean you’re healthier. It’s like “teaching to the test”; you might score better on the standardized exam but you didn’t really learn the material. 
So I am not adding one-leg standing to my daily exercise routine. But I won’t lie and tell you that, from time to time, and certainly on my 60th birthday, you may find me standing like a flamingo with a stopwatch in my hand. 
F. Perry Wilson, MD, MSCE, is an associate professor of medicine and public health and director of Yale’s Clinical and Translational Research Accelerator. His science communication work can be found in the Huffington Post, on NPR, and here on Medscape. He posts at @fperrywilsonand his book, How Medicine Works and When It Doesn’t, is available now. 
 
Any views expressed above are the author’s own and do not necessarily reflect the views of WebMD or Medscape.