There are so many questions we don’t have answers for. Some are extremely important, like “what will life with COVID be like in 2-5 years?” Others are less serious but perhaps more urgent, as in “should I keep those bananas around another day in hopes of actually making banana bread, or give up and throw them out?”
Another area where we spend a lot of time and money searching for answers is human longevity. How long will we live? What will help us live longer? What will help us live better?
A few years ago, I wrote about the sit-rise test, a candidate predictor of life expectancy. Sam wrote about it before me (we keep track of these things, so you don’t have to).
But life expectancy prediction science has moved on to other things, namely grip strength and pushups. What is their current revealed wisdom?
Okay. WHAT DO WE KNOW ABOUT GRIP STRENGTH AND PUSHUPS AS PREDICTORS OF LIFE EXPECTANCY? (I thought louder might help).
In this 2019 Atlantic article, the author cites several studies that suggest grip strength is associated with mortality risk:
In 2018, a study of half a million middle-aged people found that lung cancer, heart disease, and all-cause mortality were well predicted by the strength of a person’s grip.
Yes, how hard you can squeeze a grip meter. This was a better predictor of mortality than blood pressure or overall physical activity. A prior study found that grip strength among people in their 80s predicted the likelihood of making it past 100. Even more impressive, grip strength had good predictive ability in a study among 18-year-olds in the Swedish military on cardiovascular death 25 years later.
So what’s going on here? Grip strength is standing in as a proxy for muscle strength and (possibly erroneously) fitness in people as they age. Muscle strength decreases as we age. There’s not overall consensus on how, at what rates, where, for whom, and why, though.
More importantly, health science doesn’t know to what extent muscle loss is genetic or the result of physical activity and nutrition. In this Washington Post article, one researcher even says that grip strength doesn’t necessarily change with exercise. If that’s the case, then why are these articles using this correlation to admonish us to get out there and exercise more (including, I assume, grabbing lots of heavy things)?
This Atlantic article does have an answer. But first, a few words about the potentially prognosticatory properties of pushups.
In a study done on firefighters, researchers found that pushup tests were better at predicting cardiovascular disease than a standard treadmill stress test. Some experts think this result could extend to the general population.
“Push-ups are another marker in a consistent story about whole-body exercise capacity and mortality,” says Michael Joyner, a researcher at the Mayo Clinic whose work focuses on the limits of human performance. “Any form of whole-body engagement becomes predictive of mortality if the population is large enough.”
Hmmm… I guess this means we can just set up hula hoop testing at the local registries of motor vehicles and polling places, and then we’ll know all we need to about people’s overall health?
What makes health expects so psyched about these sorts of one-and-done health tests is that they are 1) cheap; 2) quick and easy to administer; and 3) believed to offer a snapshot of someone’s overall physical capacities, says the Atlantic article. But do we know this, above and beyond the broad population correlation studies (which have their own limitations)?
We do know, for instance, that grip strength declines over time in the absence of disease. We know that osteoarthritis and lots of other common physical conditions interfere with pushup abilities. We don’t know how lower grip strength in younger populations correlates with anything. And, we have no idea whether these statistically significant mortality risks are clinically significant (that is, whether the increased risk will translate into diagnosed clinical conditions).
We do have a lot of evidence that physical activities of many sorts are good for us. They can feel good, they can help us feel good after doing them, and they can bring us together with other people, which also feels good. That’s good.
One last question, Magic 8 Ball: will I make banana bread with those overripe bananas in my kitchen?
Readers, what do you think about these one-and-done overall life expectancy tests? Are you working on your grip strength while reading this? Let me know what you think.
When I was first trained as an Occupational Therapist, my mentor insisted I test the grip strength of every one of my patients. We used it routinely with stroke patients to assess the loss of strength on the affected side. She said we should do it with every patient so we would have an objective baseline measure of their strength in case they ever had a stroke in the future. (Usually it is compared to age- and gender-based norms.) Maybe she was onto something?
Personally, I think attaching too much meaning to a single number is dangerous. If we establish that there is a correlation between this number and longevity in a population that does not train for it, and then people start training (thinking that increasing grip strength will increase lifespan), that correlation will likely disappear and people will have wasted their time on the newest fad exercise – unless we find the wholly-unintuitive result that increasing grip strength all by itself causes increased lifespan. That seems pretty unlikely (and would take a generation to study – and even then be almost impossible to administer the study accurately).
Thanks for the comments; yes, I completely agree with you. One number does not paint a whole picture, and can even be misleading. At the same time, picking some metric for baseline and progression over time can be super-useful. It’s all in the details, isn’t it?
Oh it’s great to replay the classics! Push ups and grip tests were staples of annual military fitness training. Like you said, a quick and cheap test that gives you numbers. For occupational purposes where there’s a requirement to do physical things those tests help folks evaluate their fitness program.
But predicting longevity? A stretch to say the least.
If they did every life insurance company would have these tests as part of the application.