Disuse atrophy is best described as which of the following?

• A. Loss of muscle mass and strength due to prolonged immobilization
• B. Loss due to nerve injury
• C. Increase in muscle mass with exercise
• D. Bone loss due to disuse

Answer: (A)

Disuse atrophy happens when a muscle isn’t used for an extended period, such as after immobilization from an injury. The lack of mechanical loading reduces signals that keep muscle protein synthesis going and can increase protein breakdown, so the muscle fibers shrink and overall strength and size decline. This accurately describes the scenario of losing muscle mass due to not using the muscle.

It’s helpful to contrast this with nerve injury, which causes a different form of atrophy (neural loss of input to the muscle). It’s also not about gaining muscle—exercise-induced growth is called hypertrophy, not atrophy. And bone loss from not using a limb is disuse osteoporosis, which affects bone, not muscle.