How hard you can squeeze a tennis ball directly linked to how long you'll live for
If you want to do a quick health test and give yourself an estimate of how long you've got left to live then all you need is a functioning hand and a tennis ball.
Most people have two of the former, though the latter you'll have to acquire yourself.
If a tennis ball can't be found then some kind of stress ball will do, and what you have to do is squeeze it as hard as you can for a lengthy period of time.
Keeping the ball strongly squeezed for between 15 and 30 seconds is a good area to aim for, according to University of Derby researcher Joshua Davidson who told the BBC testing your grip strength was one of the most reliable ways to test how healthy you were.
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He said: "All you need is any object that you can grasp and can be deformed without causing pain or discomfort. Simply squeeze it for as long as you can before your grip fatigues."
While your lifespan isn't going to be solely determined by your grip strength the test is an indicator of your overall musculoskeletal strength which can point towards whether a person is getting enough exercise or living a lifestyle that is too sedentary.
There's an awful lot about modern life that involves sitting down and not physically moving around very much, and if you're keeping track of your grip strength then you'll be able to spot any decline in your ability.
Changes could be a sign of growing frail or some other kind of health complication that you might not initially realise you have.
Scientists found in a study of 140,000 adults that grip strength was a better indicator for premature death than other health factors like blood pressure.
Other studies found that people who lived to the ripe old age of 100 were 2.5 times more likely to be in the top third of grip strength for their age group.
Squeezing a tennis ball day after day should also help build up your grip strength, but in general if your physical health isn't where you want it to be then getting up and about to do something about it is your best course of action.
When having weaker grip strength is associated with a higher risk of premature death and cardiovascular disease, researchers reckon it'd be best if you were able to get a bit stronger.
Ed Jones once told the Nutrition World Podcast there was another grip strength test you could try which would require a bit more heavy lifting than squeezing a tennis ball.
He said: "If you can't hold a dumbbell that's 3/4ths of your weight for one minute, you will die earlier than you would if you were stronger. That beats cholesterol, it beats every blood test."
Then again, that sounds like a rather heavy dumbbell to be three-quarters the weight of a grown adult.
Meanwhile, another popular longevity test that requires no additional equipment is the one where you sit down and stand up again without holding onto anything or using another object to support your weight.
The harder you find getting back up without assistance the greater your chance of premature death.
Joe Harker