Association between weight loss and spontaneous changes in physical inactivity in overweight/obese individuals with knee osteoarthritis: an 8-week prospective cohort study.

Objective To describe spontaneous changes in time spent being physically inactive that is measured continuously by accelerometry during an 8-week weight-loss intervention in overweight/obese individuals with knee osteoarthritis (OA). Methods This study was designed as an observational cohort study including individuals from an OA outpatient clinic who were concomitantly overweight/obese and had symptomatic knee OA. Participants completed an 8-week dietary intervention that had been previously shown to induce substantial weight loss. The main outcome was accelerometer-based measurement of daily physical inactivity for 24 hours during the 8-week intervention period that was presented as change in the average daily time spent inactive (sitting, reclined, or sleeping) from 1 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% confidence interval [95% CI] -13.2, -12.1; P < 0.0001) after 8 weeks, which corresponded to a decrease in body mass index of 4.3 kg/m(2) (95% CI -4.5, -4.2; P < 0.0001). Significant improvements in OA symptoms (assessed by the Knee Injury and Osteoarthritis Outcome Score [KOOS]) was found across all subscales; an improvement of 12.8 points (95% CI 10.6, 15.0; P < 0.0001) was observed for pain using the KOOS. 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, 29.7]; P = 0.41). Conclusion Physical inactivity remains stable despite a clinically significant weight loss and improvements in knee OA symptoms. Change in inactivity does not seem to occur spontaneously, suggesting that focused efforts to reduce inactive behaviors are needed.