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

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. The technique is recognized as a fundamental principle for success in various forms of strength training

Strength training

Strength training is the use of resistance to muscular contraction to build the strength, anaerobic endurance, and size of skeletal muscles. There are many different methods of strength training, the most common being the use of gravity or elastic/hydraulic forces to oppose muscle contraction...

 programmes including fitness training, weight lifting

Weight training

Weight training is a common type of strength training for developing the strength and size of skeletal muscles. It uses the weight force of gravity to oppose the force generated by muscle through concentric or eccentric contraction...

, high intensity training

High intensity training

High Intensity Training is a form of strength training popularized in the 1970s by Arthur Jones, the founder of Nautilus. The training focuses on performing quality weightlifting repetitions to the point of momentary muscular failure...

 and physical therapy

Physical therapy

Physical therapy , often abbreviated PT, is a health care profession. Physical therapy is concerned with identifying and maximizing quality of life and movement potential within the spheres of promotion, prevention, diagnosis, treatment/intervention,and rehabilitation...

 programmes.

Scientific principles

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

Atrophy

Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...

 and muscle atrophy

Muscle atrophy

Muscle atrophy, or disuse atrophy, is defined as a decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle. When a muscle atrophies, this leads to muscle weakness, since the ability to exert force is related to mass...

). 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

Sedentary lifestyle

Sedentary lifestyle is a medical term used to denote a type of lifestyle with no or irregular physical activity. A person who lives a sedentary lifestyle may colloquially be known as a couch potato. It is commonly found in both the developed and developing world...

. 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. .

Methodology

In order to minimize injury and maximize results, the novice begins at a comfortable level of muscular intensity and advances towards overload of the muscles over the course of the exercise program. Progressive overload requires a gradual increase in volume, intensity, frequency or time in order to achieve the targeted goal of the user. In this context, volume and intensity are defined as follows:

• Volume is the total number of repetitions multiplied by the resistance used as performed in specific periods of time.

• Intensity is the percent value of maximal functional capacity, or expressed as percent repetition maximum.

This technique results in greater gains in physical strength and muscular growth, but there are limits. An excess of training stimuli can lead to the problem of overtraining

Overtraining

Overtraining is a physical, behavioral, and emotional condition that occurs when the volume and intensity of an individual's exercise exceeds their recovery capacity. They cease making progress, and can even begin to lose strength and fitness...

.

• Overtraining is the decline in training performance over the course of a training program, often resulting increases the risk of illness or injury or decreased desire to exercise. In order to help avoid this problem, the technique of periodization
  Sports periodization
  Periodization is an organized approach to training that involves progressive cycling of various aspects of a training program during a specific period of time. It is a way of alternating training to its peak during season. The aim of periodization is to introduce new movements as you progress...
  
   is applied.

• Periodization in the context of fitness or strength training programs is the scheduling of provisions for adequate recovery time between training sessions, variety over the course of a long-term program and motivation - avoiding monotony when repeating identical exercise routines.