age-related loss of muscle mass and strength is called
Sarcopenia Sarcopenia is the degenerative loss of skeletal muscle mass (0.5–1% loss per year after the age of 50), quality, and strength associated with aging.[1] Sarcopenia is a component of the frailty syndrome. It is often a component of cachexia. It can also exist independently of cachexia; whereas cachexia includes malaise and is secondary to an underlying pathosis (such as cancer), sarcopenia may occur in healthy people and does not necessarily include malaise. The term is from Greek σάρξ sarx, "flesh" and πενία penia, "poverty".
Anatomical terms of muscle Another example is the dumbbell curl at the elbow. The "elbow flexor" group is the agonist, shortening during the lifting phase (elbow flexion). During the lowering phase the "elbow flexor" muscles lengthen, remaining the agonists because they are controlling the load and the movement (elbow extension). For both the lifting and lowering phase, the "elbow extensor" muscles are the antagonists (see below). They lengthen during the dumbbell lifting phase and shorten during the dumbbell lowering phase. Here it is important to understand that it is common practice to give a name to a muscle group (e.g. elbow flexors) based on the joint action they produce during a shortening (concentric) contraction. However, this naming convention does not mean they are only agonists during shortening. This term typically describes the function of skeletal muscles.[5]