Muscular strength is essential for recovery after an acute illness. Disuse atrophy of muscle begins within 4 hours of the start of bed rest resulting in decreases in muscle mass, muscle cell diameter, and the number of muscle fibers. Strenuous exercise of atrophic muscle can lead to muscle damage including sarcolemmal disruption, distortion of the myofibrils' contractile components, and cytoskeletal damage. Assessment of skeletal muscle for disuse atrophy is done clinically at the bedside through strength assessment. Examination of the muscle itself can be conducted through the use of nuclear magnetic resonance imaging, whereas muscle strength can be quantified with a computerized dynamometer. Biochemical markers, including creatine kinase and troponin, also are available for the assessment of skeletal muscle damage. Activity management in the critical care environment focuses on an individualized plan, developed in cooperation with the recovering patient, with the goal of preserving and improving atrophic skeletal muscle.