Relationship of skeletal muscle atrophy to functional status: a systematic research review.

In the realm of muscle atrophy research, many studies address minute details of molecular function but few examine the effects of atrophy in terms of mobility, strength, endurance, and performance of activities of daily living. The relationship between impairment and functional limitation is the focus of this research review. A wide array of studies constitute this area of inquiry, including investigations as diverse and widely disparate as molecular chemistry and space travel and populations as different as rats, healthy young men, and elderly women. Thirty-four studies were selected based on their fit with the Enabling-Disabling Model. Three paradigms of atrophy and function emerged. Adaptation reflects the plastic nature of muscle when placed under certain conditions, ranging from disuse to high-resistance exercise. Injury/loss describes damage to muscle tissue from ischemia, medications, or reloading or reperfusion trauma. Also in this category is the loss of muscle that is seen with aging. Integrity relates to the muscle's tendency to protect itself and maintain structural adjacencies and cellular proportions. Based on the 3 muscle research paradigms, the relationship of muscle atrophy to function is portrayed as a bidirectional interaction wherein form and function have an influence on each other by way of physical changes, including those of adaptation, injury/loss, or integrity. A conceptual model is constructed to reflect this relationship.