Atrophy of skeletal muscle diminishes the quality of life of a human or animal by reducing their freedom of movement. Unfortunately, muscle atrophy occurs all too commonly. Atrophy of skeletal muscle often is initiated, or enhanced, by decreased physical activity associated with senescence, postoperative repair from orthopedic surgeries, spinal cord injury, cancer cachexia, or chronic bed rest resulting from disease. Although a clinical condition, itself, may produce some atrophy of skeletal muscle, the common factor among the above afflictions is that they reduce muscle usage. To develop a scientifically rational method for preventing muscle atrophy it will be necessary to understand the mechanism(s) by which reduced load bearing triggers the loss of muscle mass.