The term 'sarcopenia' was proposed by Irwin Rosenberg as a coined word which originally means 'loss of muscle mass' in Greek. Although several diagnostic criteria of sarcopenia has been suggested by academic societies in Europe, Asia, and the United States of America, it is reported that most of them showed similar prognostic abilities for incident disability or mortality. Those criteria include muscle weakness or muscle function or both of them in addition to low muscle mass because longitudinal studies indicated that muscle mass correlated with muscle strength less than expected before, and that muscle weakness progressed with advancing age more rapidly and influenced more on incident dependency than loss of muscle mass. It is important how we implement the diagnosis of sarcopenia into daily practice and how we manage it based on the diagnosis.