The functional capacity of any organ is dependent within physiological limits upon the intensity and frequency of its activity. Although rest may be protective for a damaged organ it results in progressive loss of functional capacity for normal organs. Limitation of activity during prolonged bed rest causes significant deterioration of multiple organ systems including the skeletal, neuromuscular, cardiovascular, respiratory, urogenital, and nervous systems. Total inactivity of muscle results in loss of strength of approximately 3% per day. Neuromuscular and emotional control and intellectual performance are all impaired by prolonged bed rest. Cardiovascular function decreases during bed rest more rapidly than it is restored when activity is resumed. Years may be required to restore the calcium lost from the skeleton during immobilization.
Kottke FJ. The Effects of Limitation of Activity Upon the Human Body. JAMA. 1966;196(10):825-830. doi:10.1001/jama.1966.03100230069017