OBJECTIVE: To describe spontaneous changes in time spent physically inactive measured continuously by accelerometry during an 8-week weight loss intervention in overweight/obese individuals with knee osteoarthritis.

METHOD: This study was designed as an observational cohort study including individuals with concomitant overweight/obesity and symptomatic knee osteoarthritis from an osteoarthritis outpatient clinic. Participants completed an 8-week dietary intervention previously shown to induce substantial weight loss. The main outcome was accelerometer-based measurement of physical inactivity for 24 hours daily during the 8-week intervention period presented as change in the average daily time spent inactive (sitting, reclined or sleeping) from one week prior to intervention to the last week of the intervention.

RESULTS: A total of 124 participants completed the dietary intervention and had valid accelerometer recordings. The mean weight loss was 12.7 kg [95% CI -13.2 to -12.1; P<.0001] after 8 weeks corresponding to a decrease in BMI of 4.3 kg/m2 [95%CI -4.5 to -4.2; P<.0001]. Significant improvements in osteoarthritis symptoms (assessed by the Knee Injury and Osteoarthritis Outcome Score) was found across all subscales; for KOOS pain an improvement of 12.8 points [95% CI, 10.6 to 15.0; P<.0001] was observed. No statistically significant change occurred in the average daily time spent inactive from baseline to follow-up (mean change: 8.8 minutes/day [95% CI, -12.1 to 29.7]; P=0.41).

CONCLUSION: Physical inactivity remains stable despite a clinically significant weight loss and improvements in knee osteoarthritis symptoms. Change in inactivity does not seem to occur spontaneously, suggesting that focused efforts to reduce inactive behaviors are needed. This article is protected by copyright. All rights reserved.