Grip strength and the aging process
Some of the earliest grip-strength studies used it as a proxy for nutritional status in elderly men and women. Nourishment, in turn, predicted their ability to survive an illness or surgery.
Which makes sense; if an older person isn’t eating enough to maintain their health and vitality, their strength would decline. Declining strength would make them more susceptible to infections, hospitalizations, and postsurgical complications, leading to longer hospital stays, loss of independence, and ultimately a higher risk of death from any cause.
Along those lines, Dr. Peterson’s research team at the University of Michigan found that low grip strength is correlated with faster aging at the cellular level.
The study looked at DNA methylation, which Peterson describes as “a reflection of someone’s exposure to life events.”
For example, someone who smokes will have altered methylation patterns, compared with someone who doesn’t. Same with someone who’s had more exposure to environmental pollution.
Accelerated DNA methylation “means you’re essentially at higher risk for what are traditionally considered age-related chronic conditions,” Dr. Peterson said. Those conditions include Alzheimer’s, type 2 diabetes, chronic inflammation, and a higher risk for premature mortality.
Those things are also linked to low grip strength, which is linked to higher DNA methylation and faster biological aging.
But there’s still a missing piece of the puzzle: Why, exactly, would the strength of one’s grip be associated with so many health outcomes?
Grip strength and muscle function
“Declining muscle function is the first step of the disabling process,” said Ryan McGrath, PhD, an assistant professor at North Dakota State University, Fargo. “That’s what you can measure with a handgrip test. It helps you identify individuals at risk for the next step of the process, which is declines in physical performance.”
Dr. McGrath got involved in grip-strength research as a postdoctoral fellow at the University of Michigan, where he worked with Peterson. Like his mentor, he’s published multiple studies using data obtained with a handgrip dynamometer.
“It can be a nice tool for assessing muscle function and muscle strength,” he explained. Because the test is so easy to administer – you sit in a chair with your arm at your side and your elbow bent 90 degrees, and squeeze the device as hard as you can – researchers can work with large groups of study participants and come away with statistically powerful data.
“There are a lot of health outcomes it’s associated with,” Dr. McGrath added, “which is one of its greatest strengths and at the same time one of its key limitations.”
He compared the dynamometer with a tire gauge. Just as a tire gauge can alert you to a loss of air pressure without revealing the source of the leak, a dynamometer can’t tell you why your grip strength is deflated.
“It’s hard to specify the prognostic value,” he said. “You don’t know the next steps to take. As a standalone measurement, that’s a concern.”
That’s why his current research goes beyond simple tests of maximum grip strength to more sophisticated measurements of the rate of force development (how fast you can express strength), repeatability (how much your strength declines from your first to your second or third squeeze), and asymmetry (how big a gap there is between your right- and left-hand strength).
Any of those measures could detect a potential neural or neuromuscular issue.
In a 2020 study, for example, Dr. McGrath and his team at NDSU showed that older adults with both weakness and asymmetry in grip-strength tests were nearly four times more likely to experience functional limitations. Those limitations could affect their ability to do anything from routine chores to keeping themselves clean and fed.