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".
Rigor mortis After death, respiration in an organism ceases, depleting the source of oxygen used in the making of adenosine triphosphate (ATP). ATP is required to cause separation of the actin-myosin cross-bridges during relaxation of muscle.[2] When oxygen is no longer present, the body may continue to produce ATP via anaerobic glycolysis. When the body's glycogen is depleted, the ATP concentration diminishes, and the body enters rigor mortis because it is unable to break those bridges.[3]