This review provides a framework for the development of an operational of sarcopenia and of the potential end points that might be adopted in trials among older adults. While the clinical relevance of sarcopenia is recognized, there is currently no universally accepted definition of the disorder. The development of interventions to alter the natural history sarcopenia also requires consensus on the most appropriate end points determining outcomes of clinical importance which might be utilized in intervention studies. We review current approaches to the definition of sarcopenia and the methods used for the assessment of various aspects of function in older people. The potential end points of muscle mass, strength, muscle power, and muscle fatigue, as well as the relationships them, are explored with reference to the availability and practicality available methods for measuring these end points in clinical trials. current evidence, none of the four potential outcomes in question is comprehensive to recommend as a uniform single outcome in randomized trials. We propose that sarcopenia may be optimally defined (for the clinical trial inclusion criteria as well as epidemiological studies) combination of measures of muscle mass and physical performance. The outcome measures for clinical trials in sarcopenia is more difficult; outcomes, tailored to the specific intervention in question, may be the forward in this difficult but clinically important area.