Background: To assess the efficacy, safety, and tolerability of bimagrumab (fully human monoclonal antibody) in participants with inclusion body myositis (IBM). Methods: This multicentre, double-blind, placebo-controlled study (RESILIENT; ClinicalTrials.gov, number NCT01925209) was conducted between September 26, 2013 and January 06, 2016 at academic clinical sites in Europe, the USA, Australia, and Japan. Eligible participants (aged 36-85 years [inclusive]; modified 2010 MRC criteria) were randomly assigned (1:1:1:1) using blocked randomisation schedule (block size=4) to receive intravenous infusions of bimagrumab 10, 3, 1 mg/kg, or placebo every 4 weeks for at least 48 weeks. All study participants, sponsor, investigators, site personnel, and those performing assessments were masked to treatment assignment. 6-minute walking distance (6MWD; primary outcome measure) was assessed at Week 52 in the primary analysis population. A multivariate normal repeated measures model was used to analyse data on 6MWD. Safety was assessed by recording adverse events (AEs), electrocardiography, echocardiography, hematology, urinalysis, and blood chemistry.