Accelerometer Studies Show That Even Marginal Differences in Activity Have Noticeable Effects on Health
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Wearable accelerometers are a comparatively new development in studies of the effects of exercise and activity on health. One of the outcomes is better evidence to suggest that even activities that don't rise to the level of what most people would consider exercise do in fact make a difference - standing versus sitting, for example:

If you're 60 and older, every additional hour a day you spend sitting is linked to a 50 percent greater risk of being disabled - regardless of how much moderate exercise you get, The study is the first to show sedentary behavior is its own risk factor for disability, separate from lack of moderate vigorous physical activity. In fact, sedentary behavior is almost as strong a risk factor for disability as lack of moderate exercise. If there are two 65-year-old women, one sedentary for 12 hours a day and another sedentary for 13 hours a day, the second one is 50 percent more likely to be disabled, the study found.

The study focused on a sample of 2,286 adults aged 60 and older from the National Health and Nutrition Examination Survey. It compared people in similar health with the same amount of moderate vigorous activity. Moderate activity is walking briskly, as if you are late to an appointment.

The participants wore accelerometers from 2002 to 2005 to measure their sedentary time and moderate vigorous physical activity. The accelerometer monitoring is significant because it is objective. The older and heavier people are, the more they tend to overestimate their physical activity. Previous research indicated a relationship between sedentary behavior and disability but it was based on self-reports and, thus, couldn't be verified.

Because the study examines data at one point in time, it doesn't definitively determine sedentary behavior causes disability. "It draws attention to the fact that this is a potential problem." Studies with animals have shown immobility is a separate risk factor for negative effects on health. "This is the first piece of objective evidence that corroborates the animal data."

This is the way things usually go: causality is determined in animal studies, where you can set a parameter and see what happens, but human studies largely only produce statistical correlations. Where those correlations match up with data generated in animal studies, that is good evidence to suggest that the same causality is at work in humans.

Link: http://www.northwestern.edu/newscenter/stories/2014/02/new-sitting-risk-disability-after-60.html

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