One study found that older people who lift weights live longer, but only if they are done quickly and sparingly.
The researchers measured the muscle power of 4,000 men and women aged 40 to 85 during the six-year trial.
They discovered that those who had the ability to lift weights at speed lived longer.
But gym users should not go too far, because those with significantly more muscle strength than average are up to 13 times more likely to die.
Muscle power is needed to perform everyday tasks, such as climbing stairs, according to experts.
The study measured the muscle strength of nearly 4,000 non-athletes by counting the number of times they were able to lift a weight in the "straight row" position.
To do this, the participant holds a weight at the hips and wears it at shoulder height with the elbows in the back.
The researchers said it was a common movement used in everyday life to pick up shopping bags and grandchildren.
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Professor Claudio Gil Araújo, Brazilian author of the study, said: "Physicians should consider measuring muscle power and advise to strengthen their training."
The research team is currently examining the link between muscle power and some causes of death, including heart disease and cancer.
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The researchers said that the best way to increase muscle power is to choose several exercises for the upper and lower body, choosing a weight that is not too easy or difficult to lift; Then do one to three sets of six to eight repetitions by moving the weight as quickly as possible with 20 seconds of rest between each set.
Start with six repetitions in each set and, when the exercise becomes easy, increase it to eight.