The shrinking or wasting away of cells, organs, or tissues that may occur as part of a disease process, trauma, or aging.

A theoretical concept that defines periods of accelerated declines in muscle mass and functional capacity.^[1] Catabolic crisis can occur at any age, but it is most common among older adults, for whom injuries, surgeries, or prolonged illnesses dictate long and perhaps frequent periods of physical inactivity or immobilization. Strategies to reduce the risk of a catabolic crisis include providing adequate nutritional support and physical therapy.^[1]

An essential amino acid that plays important roles in muscle building and repair. Leucine is one of three branched-chain amino acids, so named for their branching structures. It is a ketogenic amino acid, meaning that it serves as a precursor for ketones produced in the body. Leucine is found in many foods and is particularly abundant in protein powders derived from whey, soy, or peas.