What is the primary effect of bed rest on muscles?

• A. Increased muscle strength.
• B. Disuse atrophy and muscular deconditioning.
• C. No change in muscle mass.
• D. Muscle hypertrophy.

Answer: (B)

Inactivity from bed rest leads to disuse atrophy and muscular deconditioning. When muscles aren’t loaded through regular movement, the body’s stimulus to maintain muscle tissue drops. This shifts the balance toward muscle protein breakdown, so muscle fibers shrink and lose contractile proteins like actin and myosin. As a result, muscle cross-sectional area decreases, strength falls, and endurance or fatigue resistance declines. In short, without activity the muscles weaken and become less capable—a process known as disuse atrophy and deconditioning. The other options describe outcomes that would require muscle use or growth (strength increases or hypertrophy) or contradict the expected changes in bed rest, where some change in muscle mass and function is typical.