Background/Purpose: Adults with knee osteoarthritis (OA) are thought to have elevated levels of sedentary behavior (SB). The Sedentary Behavior Research Network defines SB as total time spent seated or lying during waking hours at < 1.5 metabolic equivalents (METs), with 1 MET being the amount of energy spent sitting at rest. SB is important to accurately measure, given its role as a risk factor for pain and functional limitation in adults with knee OA, and its recent inclusion in public health guidelines. Traditionally, SB has been measured via self-report, with responses ranging from 5-11 hours/day; however, the accuracy of self-report is questionable due potential recall bias, i.e., from long durations of SB. When SB has been measured objectively, the monitors used were unable to differentiate between sitting and standing, a key part of defining SB. Fortunately, recent innovations in activity monitoring technology can now measure body position and METs, allowing for a more exact measure of SB time. Therefore, the purpose of this study is to provide a preliminary estimate of SB measured by activity monitoring devices in men and women with knee OA.

Methods: We included participants from an ongoing randomized clinical trial called Delaware Physical Exercise and Activity in Knee osteoarthritis (PEAK). Delaware PEAK included adults who met National Institute for Health and Care Excellence (NICE) criteria for knee OA (age ≥ 45 years, activity limiting knee pain, and morning stiffness < 30 min), spent < 60 min/week performing regular exercise, and did not have a scheduled knee replacement. All participants with ≥ 5 valid days of wear time for both the thigh-worn activPAL (figure) and waist-worn Actigraph GT3X monitor were included in our analysis. We defined a valid day as wearing the activPAL for 24 hours and the Actigraph for ≥ 10 hours while awake. We used the activPAL to classify body position as seated/lying, standing, or walking, and the Actigraph to classify a behavior as ≥ or < 1.5 METs. Using SAS, R software, and the Sojourn package we calculated the total time and percent of waking hours in SB, outlined as time sitting or lying at < 1.5 METs and not including sleep. Means and standard deviations were calculated for the entire sample and for each gender (women and men).

Results: 30 participants (59.7 ± 8.0 years, 77% women, 77% white) with knee OA completed their baseline measurements resulting in an average of 11.2 ± 3.6 hours/day of SB, equating to 70.4 ± 22.5% of waking hours. In general, men tended to have more absolute SB time than women. However, men and women spent a similar percentage of their waking hours in SB (Table).

Conclusion: We used a novel method that combined the activPAL and Actigraph monitor’s data to objectively measure SB in a small cohort of adults with knee OA. Our preliminary estimates of SB are on the high end of earlier values estimated from self-reports, e.g., 11.2 vs 5-11 hours/day, respectively. Furthermore, men tended to be more sedentary than women in absolute time, however, were similar as a percentage of total waking hours.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-preliminary-estimate-of-objectively-measured-sedentary-behavior-in-knee-osteoarthritis/