Disuse

Disuse is the state in which a body part, organ, tissue, or system is not used to its normal extent. In biology and medicine, disuse can cause functional decline and structural changes, including disuse atrophy of muscles and disuse osteoporosis of bone. The term also extends to non-biological objects or infrastructures that are no longer used.

Common causes are immobilization after injury, casting, paralysis, chronic illness, aging, and prolonged inactivity. In astronauts, microgravity promotes disuse effects. Biologically, lack of mechanical loading lowers protein synthesis and increases breakdown in muscle, leading to atrophy; bones lose mineral density; joints may stiffen; and connective tissues may weaken.

Effects vary by tissue and duration. Muscles may lose mass and strength; bones may become more fragile; joints may have reduced range of motion; and circulation and metabolic function can be affected. Reversibility depends on the tissue and the length of disuse; muscles and bones can regain mass and strength with loading and exercise, but prolonged disuse can cause lasting deficits and higher injury risk.

Prevention and management emphasize early mobilization and graded rehabilitation after illness or injury. Physical therapy, resistance training, and progressive loading help restore function. Adequate nutrition, including protein and calcium/vitamin D, supports recovery. In clinical practice, minimizing unnecessary immobilization and designing rehabilitation plans tailored to the patient are central.