Progressive overload is the gradual increase of stress placed upon the body during exercise training. It was developed by Thomas Delorme, M.D. while he rehabilitated soldiers after World War II. The technique is recognized as a fundamental principle for success in various forms of strength training programmes including fitness training, weight lifting, high intensity training and physical therapy programmes.
A common goal for any strength training program is to increase or at least maintain the user's physical strength or muscle mass. In order to achieve new results, as opposed to maintaining the current strength capacity, the muscles (see skeletal muscles) need to be overloaded, which stimulates the natural adaptive processes of the human body, which develops to cope with the new demands placed on it.
Progressive overload not only stimulates muscle hypertrophy, it also stimulates the development of stronger and denser bones, ligaments, tendons and cartilage. Progressive overload also incrementally increases blood flow to the region of the body . Furthermore, progressive overload stimulates the development of more responsive nerve connection between the brain and the muscles involved.
Conversely, decreased use of the muscle results in incremental loss of mass and strength, known as muscular atrophy (see atrophy and muscle atrophy). Sedentary people often lose a pound or more of muscle mass annually. The loss of 10 pounds of muscle every decade is one troubling consequence for people choosing a sedentary lifestyle. The adaptive processes of the human body will only respond if continually called upon to exert a greater magnitude of force to meet higher physiological demands.