The target population for clinical trials aimed at sarcopenia depends on the goals of treatment and the expected natural history of sarcopenia. Based on a natural history where loss of muscle mass and/or quality leads to loss of strength, and eventually to reduced mobility and functional dependence, treatment goals can be defined for both preventive and therapeutic interventions. For example, a target population with low muscle mass and poor strength could be treated to prevent the onset of mobility disability, or a target population with low muscle mass and poor strength with mobility disability could be treated therapeutically to improve mobility. Eligibility for a trial should also be based on careful consideration of factors that affect 1) the ability to respond to treatment, 2) the safety of treatment, 3) expected prevalence and 4) feasibility.