Pushing a shopping cart or a vacuum doesn't take a lot of effort, but enough of this sort of light physical activity every day can help people with or at risk of knee arthritis avoid developing disabilities as they age, according to a new Northwestern Medicineฎ study.
It is known that the more time people spend in moderate or vigorous activities, the less likely they are to develop disability, but this is the first study to show that spending more time in light activities can help prevent disability, too.
"Our findings provide encouragement for adults who may not be candidates to increase physical activity intensity due to health limitations," said Dorothy Dunlop, professor of medicine at Northwestern University Feinberg School of Medicine and lead author of the study. "Even among those who did almost no moderate activity, the more light activity they did, the less likely they were to develop disability."
Results of the study were published April 29 in the British Medical Journal.
The scientists identified a group of almost 1,700 adults, ages 45 to 79, from the Osteoarthritis Initiative study who were free of disability but were at elevated risk for developing it because they had knee osteoarthritis or other risk factors for knee osteoarthritis, such as obesity.
Knee osteoarthritis commonly leads to disability, preventing people from engaging in activities essential to independent living and quality of life, such as dressing, bathing, walking across a room or making telephone calls, managing money and grocery shopping. Two-thirds of obese adults are expected to develop knee osteoarthritis during their lifetime.
To track the amount and intensity of physical activity these at-risk people engaged in every day, scientists had them wear an accelerometer during waking hours for about a week. The device is worn around the hip and measures the intensity of movement. The data collected reveals how much time is spent in vigorous, moderate or light activities.
Two years after collecting the results from the accelerometer, participants were surveyed and asked about the development of disabilities. As expected, more time spent in moderate or vigorous activity was associated with lower reports of disabilities, but researchers were pleased to find that greater time spent in light intensity activities also was related to fewer disabilities, even after accounting for time spent in moderate activities.
Those who spent more than four hours per day doing light physical activity had more than a 30 percent reduction in the risk for developing disability compared to those spending only three hours a day in light activity (the least average number of hours collected in the study).
The findings controlled for time spent in moderate or vigorous physical activity and other predictors of disability, both demographic and health factors.
"We were delighted to see that more time spent during the day, simply moving your body, even at a light intensity, may reduce disability," Dunlop said. "Now people with health problems or physical limitations, who cannot increase the intensity of their activity, have a starting place in the effort to stay independent."
- D. D. Dunlop, J. Song, P. A. Semanik, L. Sharma, J. M. Bathon, C. B. Eaton, M. C. Hochberg, R. D. Jackson, C. K. Kwoh, W. J. Mysiw, M. C. Nevitt, R. W. Chang. Relation of physical activity time to incident disability in community dwelling adults with or at risk of knee arthritis: prospective cohort study. BMJ, 2014; 348 (apr28 6): g2472 DOI: 10.1136/bmj.g2472
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