Sampling and recruitment
RECRUITMENT
A stratified purposive sampling strategy was employed to sample participants from the REACT intervention arm and ensure rich and diverse experiences. Participants were stratified and assigned to one of four groups according to their attendance at group exercise sessions and their physical functioning at baseline (Table Interview sampling matrixFor sampling, attendance was classified as high when attending at least 50% of group-exercise sessions, and low when attending less than 50%. SPPB scores were categorised as frail or prefrail. Scores of 4–7 were considered frail/Low SPPB and scores from 8 to 9 considered pre-frail/High SPPB (frailty-classification recommendations of the European Medicines Agency) [All session leaders involved in the delivery of the REACT programme were invited for interviews after the completion of the 12-month group programmes they were leading. Informed written consent was obtained from participants during recruitment to the REACT study (Additional file 