Grip strength is associated with a range of health outcomes, from type 2 diabetes to depression. Here’s how to check yours.

In a world of technologically-driven longevity clinics with their increasingly sophisticated imaging scans, some of which can cost tens of thousands of dollars, it turns out that one of the best assessments of muscle strength and quality is to simply sit in a chair and squeeze a tennis ball.

That's the recommendation offered by Joshua Davidson, a strength and conditioning researcher at the University of Derby who studies hand grip strength, a metric increasingly recognised as one of the most reliable markers of human health.

When testing grip strength in clinical trials, scientists typically use a hand dynamometer, a device which you squeeze as hard as possible to measure the force generated by the muscles in your hand and forearm. Several companies are now attempting to take the dynamometer out of the clinic and into the home, combining easy-to-use devices with mobile apps to let anyone chart their grip strength over time.

However, according to Davidson, you can still get a decent idea through a simple "squeeze test" with a tennis or stress ball. "All you need is any object that you can grasp and can be deformed without causing pain or discomfort," he says. "Simply squeeze it for as long as you can before your grip fatigues. Being able to maintain a maximal squeeze on something like a tennis ball for 15-30 seconds would be a good standard to strive for." Noting down how long you can squeeze can help you track your grip strength over time.

Of course, as Mark Peterson, a physical medicine and rehabilitation professor at the University of Michigan points out, having a weak grip strength alone will have relatively little impact on your everyday life directly, beyond making it a little bit harder to open cans or jars. But researchers are increasingly using grip strength as a proxy for overall musculoskeletal strength throughout the body. It can reflect whether a person is active enough or too sedentary and indicate their risk of frailty – the condition of being vulnerable as a result of a decline in one's physiological health.

This first came to scientists' attention through a particularly notable study of nearly 140,000 adults across high, middle and low-income countries which found grip strength was a better predictor for premature death than other more obvious indicators such as blood pressure.

Other research has revealed that a person's grip strength can indicate their likelihood of living past 100. In one study, volunteers had their grip strengths measured in 1965-1968, when they were between 56 and 68 years old, and their survival was tracked for the next 44 years. Those who became centenarians were 2.5 times more likely to have had grip strength results in the highest third, compared to those who died before the age of 79.

Darryl Leong, an associate professor of medicine at McMaster University in Canada, explains that your handgrip strength – and therefore your overall muscular strength – is a sum of your nutrition, physical activity and whether you have any illnesses. "This is the reason it's associated with so many health outcomes," he says.

One study which used dynamometer........

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