Active Voice: Do People Sit Less or Move More After Total Knee Replacement?

By Sandra C. Webber, Ph.D., M.Sc., BMR(PT)

Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.

Sandra C. Webber, Ph.D., M.Sc., BMR(PT), is a physical therapist, teacher and researcher in the Department of Physical Therapy, College of Rehabilitation Sciences, University of Manitoba, Winnipeg, MB, Canada. Her research focuses on objective measurement of activity performance (what people do in their everyday lives) including physical activity, ambulation and sedentary behavior in older adults and individuals with chronic disease.

This commentary presents Dr. Webber’s views on the topic of a research article which she and her colleagues authored. Their article appeared in the June 2017 issue of
Medicine & Science in Sports & Exercise® (MSSE).

Popular media often promotes sitting as the “new smoking” because it is associated with health risks. While evidence suggests that not all sitting is “equally bad” (e.g., depending on an individual’s lifestyle, physical activity level and socioeconomic status), we do know that for people with chronic conditions, sedentary behavior is linked to additional health risks. In people with osteoarthritis, high levels of sedentary behavior are associated with metabolic syndrome, diabetes and heart disease. Further, osteoarthritis is associated with subsequent physical decline and high blood pressure — independent of time spent in moderate-to-vigorous activity.

People with end-stage osteoarthritis often progress to have total knee replacement surgery, which usually results in substantial reductions in pain. However, despite this improvement, previous research has demonstrated that physical activity levels increase only slightly after recovery from surgery and patients continue to be less active compared to healthy individuals. Little is known about what happens to sedentary behavior levels after people have knee replacement surgery.

In our study, reported in the June 2017 issue of MSSE, we collected seven-day activity monitor data (ActiGraph GT3X+) in 32 people with severe knee osteoarthritis who were waiting for knee replacement and in 38 individuals one year after knee replacement. There were no differences in total sedentary time (9-10 hours per day) between the groups. Both groups also averaged 3-4 lengthy periods of sitting (30 minutes or more) each day. In terms of physical activity, the number of steps per day were marginally greater in people with knee replacements and they demonstrated slightly higher peak walking speeds compared to those on the waiting list. There were no substantial differences in moderate-to-vigorous physical activity levels between the groups.

We found that sedentary behavior and physical activity levels were similar among people awaiting knee replacement surgery and those who were one year post-knee replacement. In the post-operative individuals, daily walking behaviors (at slow, moderate and brisk paces) and engagement in moderate-to-vigorous physical activity were less than found in the general population. The fact that markers of sedentary behavior (as well as physical activity) do not substantially improve after knee replacement suggests that elevated risks related to reduced physical function, increased blood pressure and other cardiovascular/metabolic diseases likely persist. Although most patients have little to no knee pain after knee replacement, this does not seem to noticeably influence sitting behavior or activity levels. Thus, additional rehabilitation and education strategies are warranted after the acute recovery stage; these should include enhancing awareness of the health risks and interventions to sustain increases in physical activity behaviors.

Supporting patients in their efforts to break up and reduce overall sedentary time and increase physical activity may reduce present and future health risks, enhance function and increase quality of life.