There is growing evidence that time spent sitting — in cars, at offices and on the couch — is having some seriously negative effects on health. Sedentary behavior has been linked to obesity, heart disease, diabetes and other chronic conditions.
But a new study provides encouragement that some physical activity, including relatively simple ways to improve muscle strength, may be enough to overcome some of the unhealthy effects of sitting too much.
In a study published in BMC Medicine, researchers led by Carlos Celis-Morales from the University of Glasgow analyzed data from nearly 400,000 middle-aged people in the UK. The scientists compared people’s reports on how much physical activity they did to their reports on how much time they spent in front of a TV or computer screen. To get more objective measures of people’s exercise levels, the scientists also conducted tests of grip strength, in which people squeezed a specialized device to measure their muscle strength, as well as fitness tests on an ergometer. While fitness tests are time consuming and expensive, grip strength is a useful proxy for how physically active and fit people are, says Celis-Morales, since it measures overall muscle strength and can be done quickly and easily by most doctors during an office visit.
People who had the weakest grips had a 31% higher risk of dying over the study’s five-year follow-up for every two hours they spent in front of a screen, compared to people with stronger grips who spent similar amounts of time sitting down. These people also had a 21% higher risk of developing heart disease and a 14% higher risk of getting cancer, compared to people with higher grip strength.
Essentially, for every two hours people spend sitting in front of a TV or computer, the risk of dying from any cause is about two times higher among people with lower grip strength than people with higher grip strength.
The good news is that grip strength can be improved by weight training and moderate increases in physical activity and fitness, Celis-Morales says. “The overall message is that it may not matter so much if you watch a lot of TV if you are strong, fit and physically active,” he says. “If you move and are more active, [sitting] will not have the same effect on your health as if you are inactive.”
It’s important to remember that sitting too much is still unhealthy, he says; compared to people who don’t sit as much, people who are more sedentary have higher rates of early death and chronic diseases. But among those must sit for most of the day, being more active can offset some of those detrimental effects.
“Sometimes there nothing you can do at work if you spend eight hours in front of a computer or in a chair,” he says. “But when you go home, you can modify your behavior. You can do a lot of things to offset the effect of spending so many hours sitting during the day.”
The results also suggest that recommendations that many countries have adopted recently — like those urging everyone to move more and sit less — may not be so effective for everyone, he says. Those guidelines may apply more to people who are both sedentary and relatively inactive; encouraging these people to exercise a little more could help them to avoid some of the negative health consequences of their sedentary behavior.
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