Immobility occurs as a result of a process of degeneration that influences nearly all organ systems due to altered gravitation forces and decrease of motor function. Immobility or disuse appears most pronounced on the musculoskeletal system. These changes occur during the early stages after immobilization and are directly associated with diminished movement and weight-bearing stress. Due to the fact that the primary role of the musculoskeletal system is to support the body against gravity and move the body in space, loss of function of the musculoskeletal system will have a critical effect on a person’s functional mobility.
Immobilization and loss of use are significantly related to muscle weakness. As an example, patients who undergo strict bed rest lose 1 to 1.5% of their strength per day. Long periods of immobilization can result in total muscle strength loss by as much as 40%.
Due to the fact that muscle strength corresponds to a cross-sectional area of a muscle, measuring muscle circumference can be used to grade progressive atrophy. At the cellular level, the likelihood of slow-twitch fibers (type I) to atrophy is greater than fast-twitch fibers (type II). As loss of muscle progresses, the number of muscle fibers stays the same; however, the size of the fiber shrinks, and a proportionate increase in connective tissue results.
The treatment of muscle atrophy requires early administration of remobilization and strengthening exercise whenever possible. There is a vast amount of evidence that training prior to immobilization decreases the progression of strength loss and that maintenance of joint range of motion can slow muscle atrophy. However, once strength is lost, it usually takes twice as much time to regain muscle strength as it did to lose it. Consequently, the longer one is immobilized, the longer it will take for one to recover.
Older adults clearly benefit from strength-training interventions. Strength increases occur directly as a result of muscular hypertrophy and the supplemental influence of enhanced neural recruitment and motor unit coordination within the central nervous system.