Updated concept of sarcopenia based on muscle-bone relationship.

Sarcopenia is an age-related loss of skeletal muscle mass and strength. It has been widely recognized that low muscle mass was essential in the diagnosis of sarcopenia, whereas recent studies have emphasized the importance of muscle strength. In practice, muscle quality as well as muscle mass might determine the strength and physical performance. A new diagnostic algorithm of sarcopenia has recently been established, in which low muscle strength is a key characteristic factor for the diagnosis of sarcopenia. Although many factors are supposed to be involved in the pathology and development of sarcopenia, precise mechanisms remain to be elucidated. Recent studies have also focused on the crosstalk between muscles and bones, including functional involvement of myokines and osteokines.