BackgroundPhysical rehabilitation (PR) interventions can improve physical function for adults with frailty; however, participant retention rates in randomized controlled trials (RCTs) are unknown.Objective is to summarize participant retention rates in RCTs of PR for adults with frailty.Design is a systematic review and meta-analysis (DOI:10.17605/OSF.IO/G6XR2).Participants are adults ≥ 18 years with frailty.Setting consists of inpatient, outpatient and community-based interventions.Intervention includes any PR intervention.MethodsWe searched 7 electronic databases from inception to April 15, 2020 for published RCTs. Our primary outcome was participant retention rate to primary outcome measurement. Secondary outcomes included retention by study group, participant retention to intervention completion, reported reasons for attrition and reported strategies for maximizing retention. We completed screening, data extraction and risk of bias (ROB) assessments independently and in duplicate. We conducted a meta-analysis, calculating retention rates and 95% confidence intervals (CIs) using fixed or random-effects models, as appropriate.ResultsWe included 21 RCTs, enrolling 1685 adults with frailty (median age 82.5 years (79.0, 82.2), 59.8% female (57.5, 69.8)). Twenty RCTs reported retention data, of which 90.0% (n = 18) had high ROB. The pooled participant retention rate to primary outcome measurement was 85.0% [95%CI (80.0, 90.0), I2 = 83.9%, p < 0.05]. There were no differences by group for retention to the primary outcome [intervention 87.0% (83.0, 91.0), p < 0.05, comparator 85.0% (79.0, 90.0), p < 0.05] or in retention to intervention completion [83.0% (95.0% CI (78.0–87.0), p < 0.05]. Of the 18 studies reporting 24 reasons for attrition, 51.3% were categorized as potentially modifiable by the research team (e.g. low motivation). Only 20.0% (n = 4) of studies reported strategies for maximizing retention.ConclusionsIn this review of 21 RCTs of PR, we identified acceptable rates of retention for adults with frailty. High retention in PR interventions appears to be feasible in this population; however, our results are limited by a high ROB and heterogeneity.