Frailty modifies the intervention effect of chair yoga on pain among older adults with lower extremity osteoarthritis: Secondary analysis of a nonpharmacological intervention trial

{Objective: In an 8-week nonpharmacological pain intervention trial among older adults with lower extremity osteoarthritis (OA), we aimed to examine: a) the baseline frailty level of the participants; b) whether such intervention is more beneficial for baseline frailer older adults than for their counterparts with less frailty; and c) whether the intervention could also alter frailty. Methods: Participants were randomly assigned to either chair yoga (CY) or health education program (HEP) groups and attended twice-weekly 45-minute CY or HEP sessions for 8 weeks. Following a standard procedure, 82 variables were used to construct a frailty index (FI, 0-1). Primary outcomes were: Western Ontario and McMaster Universities (WOMAC) pain and pain interference. Linear mixed-effects models were used to evaluate the modifying effect of baseline frailty on the intervention effect of CY on primary outcomes. Similar models were used to evaluate the effect of CY on frailty. Results: A total of 112 participants (n = 63 CY