RecruitingBehavioural interventionImpact of Exercise on the Complications of Corticosteroids in Patients With GVHD: the RESTART TrialThis study is about determining if an aerobic and resistance exercise intervention is feasible in patients diagnosed with acute or chronic GVHD (Graft-Versus-Host Disease) after having an allogeneic stem cell transplant. The names of the study interventions involved in this study are: * Aerobic and resistance exercise (A+R) - Home-based aerobic and resistance exercise program * Attention control (AC) - Home-based stretching program