Grip Strength Is a Crucial Vital Sign Your Doc Has Never Taken

Why grip strength? How could the amount of force generated by such small muscles in the hand and forearm be connected to so many life-and-death consequences?

Survival of the Strongest

The first thing to understand about grip-strength testing is that it’s only partially about grip. It’s mostly about strength. That’s what attracted Peterson to this line of research. 

“I’m a former strength coach, so I wanted to make a case for why strength was important across populations, not just athletes,” he said.  “I strongly believe in strength preservation and healthy living as a predictor for longevity.”

Consider a classic study of Swedish army recruits. Because of Sweden’s post-World War II conscription policy, virtually every young male in the country underwent a physical examination to see if they were fit for military service — an exam that included a grip-strength test. 

That gave the researchers a database with more than a million participants. They followed up on them decades later through publicly available records.

What they found: The men with the weakest grip strength in their late teens were 20% more likely to have died by their mid-50s, compared to those with moderate to high grip strength. Even suicide rates were 20% to 30% higher for the weakest recruits. 

There’s a brutal Darwinian logic to the idea that a stronger person with a more powerful grip would enjoy a longer, healthier life. To our ancient ancestors, stronger hands meant you were probably better at everything that aided survival: hunting, fighting, building shelter, and bearing and rearing children. 

Those with such an advantage would be more desirable to potential mates. They would then conceive more children, and those children would be stronger and healthier, thanks to both genetics and nutrition.

Fast-forward to the 21st century where we must force ourselves to engage in physical activity even though science shows us again and again why it’s so important for health and longevity. The old rules still apply: Strength aids survival. 

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. 

And this 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, 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 to 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,” Peterson said.  Those conditions include Alzheimer’s, type 2 diabetes, chronic inflammation, and a higher risk of premature mortality.

As you may recall, those things are also linked to low grip strength, which we now know 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 your 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, assistant professor of health, nutrition, and exercise sciences at North Dakota State University. “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.”

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 has published lots of 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 people and come away with statistically powerful data.

“There’s a lot of health outcomes it’s associated with, which is one of its greatest strengths and at the same time one of its key limitations,” McGrath said. 

He compared the dynamometer to 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-hand and left-hand strength).

Any of those measures could detect a potential neural or neuromuscular issue. 

In a 2020 study, for example, 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.

That brings us to perhaps the most important question: once you have grip-strength data on a patient, client, or yourself, what do you do with it?

Waging War on Weakness 

Defining weakness is easy. Using dynamometer readings, the generally accepted cutoffs for low grip strength are 26 kilograms for an adult male and 16 kilograms for a female. (It’s better to use kilograms instead of pounds, as you’ll see in a moment.)

But that’s way too simple, Peterson said. 

For one thing, your age matters. Grip strength typically peaks for men in their late 20s and declines rapidly in middle age and beyond. For women, it plateaus in their 20s and gently declines until their 50s. So at a minimum, you should consult the age-based standards you’ll find included with a dynamometer. 

Another caveat: Peterson said grip strength tests aren’t very meaningful for people who actively train for strength, though he suggests dedicated athletes make up a relatively small percentage of the population – even as low as 10%.

The size of the person taking the test is also important.

“You absolutely must account for body mass in the context of understanding how grip strength, or any strength measure, is reflective of health and function,” Peterson said. 

To calculate your strength-weight ratio, (which Peterson calls “normalized grip strength”), simply divide your grip strength in kilograms by your body weight in kilograms. For men, a ratio greater than 0.70 puts you in the higher percentiles. For women it’s 0.50. (You can find a complete chart of normalized grip strength percentiles here.) 

And if the results suggest that the person in question is objectively weak? “For me, that’s easy,” Peterson said. “They need to do exercise.”

Common sense suggests doing a lot of forearm exercises for grip strength. Not so, said  Peterson. The strength of your hand and forearm muscles reflects what they can do along with all your other muscles moving together.

A 2019 study found that, for older adults, a variety of exercise programs can lead to modest but meaningful increases in participants’ grip strength – and they don’t necessarily have to include actual gripping exercises. The programs ranged from tai chi to water aerobics to walking, stretching, and all kinds of resistance training. 

Peterson’s advice to everyone is pretty straightforward: Get stronger. It doesn’t really matter how you do it or how much strength you ultimately gain. Even a little more strength means a little less weakness and a little more life.