President Trump’s odd, grabbing handshake aside, people have long judged each other for the firmness — or lack thereof — of a handshake. A strong grip generally conveys confidence or even power, while a limp grip sometimes comes across as disengaged or weak.

But recent studies indicate that grip strength can reveal far more than your personality; it can serve as a window into how healthy — or unhealthy — you are. And as you age, experts say, your grip strength can be a measure for how likely you are to develop and survive diseases such as cancer, heart disease and more.

A 2016 systematic review of many studies involving people 60 an older found that grip strength “has a predictive validity for decline in cognition, mobility, functional status and mortality.”

Experts say that handgrip strength works as a stand-in for measuring general body strength and muscle mass, which declines with age. The advantage of measuring grip strength as a marker of health, say researchers, is that it is affordable and convenient, key for rural and other populations that may not have easy access to medical care.

When President Trump shakes people's hands, the world is watching. Here's why. (Peter Stevenson/The Washington Post)

“It’s not a perfect measure of overall muscle strength, but a good one” since loss of muscle mass is linked to many diseases and as early as midlife grip strength can be an indicator of disability later in life, says Stuart Gray, lecturer in exercise and metabolic health at the University of Glasgow’s Institute of Cardiovascular and Medical Sciences who focuses on age-related loss of muscle mass.

To measure grip strength, researchers use a simple $200 device called a dynamometer. Subjects squeeze it to reveal the amount of force applied. “It takes five to 10 minutes to train someone to use the device,” Gray says, “so it’s an easy application.”

Muscle strength and old age

Gray was one of the co-authors of a 2018 study that found handgrip strength was “strongly associated with a wide range of adverse health outcomes.” The research found an association between lower grip strength and higher incidence of cardiovascular disease, chronic obstructive pulmonary disease and various types of cancer, including colorectal, lung and breast.

The study used information from 500,000 people age 40 to 69 who enrolled in the UK Biobank, which collects data to investigate genetic, nutrition, environment and other factors affecting health.

“We knew that lower muscle strength is linked to higher morbidity,” Gray says, “but we think it has an underappreciated role in health. We wanted to probe this more deeply in a large cohort of people to see if it was associated with more conditions.”

“Muscle strength is an indicator of your ability to withstand diseases,” says Darryl Leong, a cardiologist with the Population Health Research Institute at Hamilton Health Sciences and McMaster University in Canada. “When you are stronger and you become ill, you have reserves that you can draw on to help fight the disease,” he says. “Without muscle strength, your odds are significantly poorer.”

Leong says that becoming frail is often considered an inevitable part of aging. With this research, he says, “We challenge this belief because we have observed many younger adults who are frail and many older adults who are not.”

Leong is leading an ongoing study of about 142,000 people in 17 countries that uses their grip strength to evaluate the likelihood of heart attack, stroke or death from cardiovascular disease.

“Our research indicated that low muscle strength is associated with a higher risk of dying, first and foremost,” Leong says. It also found that “grip strength was a stronger predictor of all-cause and cardiovascular mortality than systolic blood pressure.”

Leong’s research suggests for each 11-pound decrease in grip strength there is a 16 percent higher risk of dying from any cause, a 17 percent risk of dying from heart disease, a 9 percent higher risk of stroke and a 7 percent higher risk of heart attack.

The results and observations on frailty not specifically tied to age suggest the need for more research, Leong says.

“We need to understand the ingredients that lead to successful aging with preservation of strength,” he says. “We hope that a successful approach to preserving muscle strength will lead to a reduced risk of death and disability.”

One small study, in 2017 — of 22 men and 41 women between ages 60 and 94 — used handgrip strength and interviews to assess their health-related quality of life. It found that “social contacts with non-relatives and hand grip strength . . . had a significant positive impact on health related quality of life among old aged men and women.”

Grip strength, the authors said, clearly indicated the muscle strength generally of the participants, and higher strength suggested a higher physical fitness and a more independent quality of life.

Chicken or egg

While both researchers tied grip strength as a measure of overall muscle strength to disease outcomes, both said why that is isn’t so clear.

“After the age of 40, grip strength will begin to decline, even in the absence of disease,” Gray says. “Why this is we don’t know — many potential contributing factors — but it’s part of the overall sarcopenia [muscle loss] process. In fact, low grip strength is the main diagnostic criteria of sarcopenia.”

The question that remains, however, is whether that is the result of genetics and other factors or the result of not staying fit and active.

“We observed variations in muscle strength among different ethnicities,” Leong says. “Is this genetic or is it a reflection of the environment in which you grow up and the diet that you eat? We want to figure that out and help prevent a loss of grip strength.”

Gray hypothesizes that grip strength comes down to 50 percent lifestyle and 50 percent genetics. “We don’t know all the factors that come into play and grip strength doesn’t necessarily change with exercise,” he says.

Exercise and activity, however, cannot be discounted, Leong says. “It’s the old adage of ‘use it or lose it,’ ” he says. “Resistance training and strength preservation should be part of the routine as you age.”

That doesn’t mean you should train your grip strength specifically, however.

“Just improving grip strength will not improve your overall health,” Gray says.

Cathleen Colon-Emeric, head of the geriatrics division and associate dean for research mentoring at Duke University School of Medicine, says that “We should consider grip strength as an overall biomarker of health, and improving it by itself will not lead to improved outcomes.”

“Instead, we should focus on maintaining or improving muscle mass, which greatly reduces the risk for many conditions,” she says.

Gray and Leong are planning future studies to better understand what causes loss in grip strength. Meanwhile, says Leong, a healthy diet and exercise remain the best approach to healthy aging.