For the most part, inactivity in children and young adults reflects a deviation from normality. There are many diseases for which motor dysfunction and hypoactivity have been documented as being either inherent to the disease process or consequent to it. Disease often causes hypoactivity, leading to a detraining effect, a reduction in functional capacity, and an increase in neuromuscular dysfunction and hypoactivity. This cycle can occur in any chronic disease or disability leading to motor dysfunction (Bar-Or 1983). Physical exercise and activity can increase significantly aerobic endurance, neuromuscular coordination, range of joint motion, muscle strength, and endurance, can prevent or limit joint contractures, and can increase work capacity.