Treatment outcomes for clinical trials of interventions on sarcopenia depend on the goals of the intervention, especially whether the treatment is considered therapeutic or preventive. Key issues regarding outcomes are the selection of a primary outcome and options for secondary outcomes. While clinical significance and face validity are key concerns when making this determination, other factors to be incorporated into the decision include measurement characteristics, feasibility and cost, risks of missing outcomes and options for alternative strategies to determine them. Primary should be highly responsive to changes in sarcopenia and clinically important. Like many problems of aging, functional abilities, especially mobility, may be the most clinically relevant states.