3/6/15
by
Action Points
Note that this observational study of patients with knee osteoarthritis found that sedentary behavior, independent of exercise, contributed to worse physical function.
Be aware that the causal path may involve worse physical function leading to sedentary behavior, rather than the other way around.
Being sedentary worsens physical function in patients with knee osteoarthritis (OA), an association that remains independent of exercise levels, according to researchers from Northwestern University in Chicago.
In an examination of data from a substudy of the Osteoarthritis Initiative (OAI), average gait speed of adults with radiographic knee OA was significantly slower in the most sedentary group compared with the less sedentary groups. More than two-thirds of the study participants in the most sedentary behavior group did not meet the minimum walking speed to be able to safely cross a street, the authors report in Arthritis Care and Research.
Incorporating movement into the daily routine of patients with knee OA, especially for those with jobs that require sitting at a desk, is important, said lead investigator Jungwha Lee, MD. She suggests that such patients “set an alarm to get up every so often; to get up every hour for a couple minutes; print papers at the printer furthest away from their desk; after using the restroom, take a lap around the floor before returning to their desk.”
A total of 1,168 patients 49 to 83 years old (mean age, 66 years) with radiographic knee OA who participated in an accelerometer substudy of the OAI and had at least 4 days of accelerometer monitoring were included in the analysis. Their physical function was assessed by timing a 20-meter walk and completion of a chair stand test.
Sedentary behavior was measured using an accelerometer, which the participants wore on a belt during the day for 7 consecutive days. Water and cycling activities were captured by a participant log. Participants were divided into quartiles of activity level.
The participants spent a mean of 67% of their daily time in sedentary behavior, with a range of 28% to 91%. Compared with adults in the less sedentary groups, those in the most sedentary group tended to be older, nonwhite, and male, and they more frequently reported comorbidities. Gait speed on the 20-meter walk was a mean of 4.30 feet/second, and ranged from 2.21 to 7.05 feet/second.
The average gait speed among the most sedentary group was 3.88 feet/second, which was significantly slower than the speed of the less sedentary groups (4.23, 4.33, and 4.33 feet/second, respectively). Some 72% of the participants in the most sedentary group could not meet the minimum walking time required to safely cross a street, which is considered to be a walking speed of 4 feet/second, the authors note. About half of the participants in the less sedentary quartiles could not meet this threshold.
The average chair stand rate among the most sedentary group was 25.9 stands/minute, which was also significantly slower than the rates of the less sedentary groups (28.9, 29.1, 31.1 stands/minute, respectively).
Compared with the most sedentary group, average physical function was significantly better in less sedentary behavior groups based on mean differences in gait speed (unadjusted difference, P<0.0001) and chair stand rate (unadjusted difference, P<0.0001).
These trends remained significant in multivariable analyses (adjusted differences, P<0.0001 for gait speed and P=0.0016 for chair stand rate) controlling for demographic factors and health factors such as comorbidity, body mass index, knee pain, knee OA severity, presence of knee symptoms, and average daily minutes of moderate to vigorous physical activity.
The authors make a clear distinction between promoting a reduction in time spent being sedentary and promoting an increase in moderate to vigorous activity, writing that both “are likely to impart greater health benefits.”
Lee told MedPage Today that, “exercise is pre-planned, specific activity to strengthen, tone, and become more flexible. Physical activity is any activity you do, such as walking, yoga, parking your car farther away from the store, walking to the mailbox, going up and down stairs doing laundry, etc. Sometimes people feel that they don’t have time to exercise. All movements you can build into daily routine are valuable, not just formal exercise. You don’t need gym membership to promote good health.”
A limitation of the study is that accelerometers don’t capture water activities or other activities with minimal vertical acceleration/deceleration (i.e., cycling). “Also, causality cannot be inferred from these cross-sectional data as sedentary time and physical function are measured simultaneously,” they wrote.
The study was supported by grants from the National Institutes of Health (NIH)/National Institute for Arthritis and Musculoskeletal and Skin Diseases, and the Falk Medical Trust. The Osteoarthritis Initiative is a public-private partnership funded by the NIH. Private funding partners include Merck Research Laboratories, Novartis Pharmaceuticals, GlaxoSmithKline, and Pfizer. Private sector funding for the Osteoarthritis Initiative is managed by the Foundation for the NIH.
Dr. Lee’s work was supported by the Rheumatology Research Foundation.
Dr. Chang’s work was supported by the Hong Kong Research Grants Council.
A co-author’s (Dorothy Dunlop) work was supported by the Rheumatology Research Foundation.
Reviewed by F. Perry Wilson, MD, MSCE Assistant Professor, Section of Nephrology, Yale School of Medicine and Dorothy Caputo, MA, BSN, RN, Nurse Planner
last updated 03.06.2015
Primary Source
Arthritis Care and Research