Sarcopenia is the normal age-related process of muscle fiber loss. Type I muscle fibers support endurance and posture. Type II muscle fibers support strength for heavier loads and speed, as well as older adult functional independence in activities such as going up stairs and standing up from a chair. Resistance training can help slow muscle fiber loss at any age.  

For this discussion, we will examine the more microscopic underlying question: “Why do we lose muscle fibers with the aging process? Where do they go?”