Strength training is a blanket term for all exercises that develop the strength and size of skeletal muscles. There are many different methods of strength training, the most common being the use of gravity (see weight training) or elastic/hydraulic (see resistance training) forces to oppose muscle contraction. Strength training and resistance training are terms often used interchangeably, resistance training is used to refer to elastic/hydraulic training alone.

Properly performed, strength training can provide significant functional benefits and improvement in overall health and well-being including increased bone, muscle, tendon and ligament strength and toughness, improved joint function, reduced potential for injury, improved cardiac function and elevated good cholesterol. Training commonly uses the technique of progressively increasing the force output of the muscle through incremental increases of weight, elastic tension or other resistance, and uses a variety of exercises and types of equipment to target specific muscle groups. Strength training is primarily an anaerobic activity, although some proponents have adapted it to provide the benefits of aerobic exercise. This is more evident in Circuit Training.

Strength training differs from bodybuilding, weightlifting, powerlifting and strongman, which are sports rather than forms of exercise. Strength training, however, is often part of their training regimen.

Until the 20th century, the history of strength training was essentially a history of weight training. With the advent of modern technology, materials and knowledge, the methods that can be used for strength training have multiplied significantly.

Hippocrates explained the principle behind strength training when he wrote "that which is used develops, and that which is not used wastes away", referring to hypertrophy and atrophy. Progressive resistance training dates back at least to Ancient Greece, when legend has it that wrestler Milo of Croton trained by carrying a newborn calf on his back every day until it was fully grown. Another Greek, the physician Galen, described strength training exercises using the halteres (an early form of dumbbell) in the 2nd century.

Another early device was the Indian club, which came from ancient Persia where it was called the "meels." It subsequently became popular during the 19th century, and has recently made a comeback in the form of the clubbell.

The dumbbell was joined by the barbell in the latter half of the 19th century. Early barbells had hollow globes that could be filled with sand or lead shot, but by the end of the century these were replaced by the plate-loading barbell commonly used today.

Strength training using isometric exercises was popularised by Charles Atlas from the 1930s onwards. The 1960s saw the gradual introduction of exercise machines into the still-rare strength training gyms of the time. Strength training became increasingly popular in the 1980s, following the release of the bodybuilding movie Pumping Iron and the subsequent popularity of Arnold Schwarzenegger. Since the late 1990s increasing numbers of women have taken up strength training, influenced by programs like Body for Life; currently nearly one in five U.S. women engages in weight training on a regular basis

The basic principles strength training involves a manipulation of the number of reps, sets, tempo, exercise types and weight moved to cause desired increases in strength, endurance, size or shape, and or overloading of the muscle. The specific combinations of reps, sets, exercises, resistance and weight depends upon the aims of the individual performing the exercise; sets with fewer reps can be performed with heavier weights, but have a reduced impact on endurance when dealing with weights. However, resistance deals with force, pushing faster and harder or increasing the elastic pull to overload the muscles.

Strength training also requires the use of 'good form', performing the movements with the appropriate muscle group(s), and not transferring the weight to different body parts in order to move greater weight/resistance (called 'cheating'). Failure to use good form during a training set can result in injury or a failure to meet training goals - since the desired muscle group is not challenged sufficiently, the threshold of overload is never reached and the muscle does not gain in strength.

The benefits of strength training - increased muscle, tendon and ligament strength, bone density, flexibility, tone, metabolic rate and postural support. There are benefits and limitations to weight training as compared to hydraulic resistance, or elastic resistance.

Resistance training involves the use of elastic or hydraulic resistance to contraction rather than gravity. Weight training provides the majority of the resistance at the beginning, initiation joint angle of the movement, when the muscle must overcome the inertia of the weight's mass. After this point the overall resistance alters depending on the angle of the joint. In comparison, hydraulic resistance provides a fixed amount of resistance throughout the range of motion, depending on the speed of the movement. Elastic resistance provides the greatest resistance at the end of the motion, when the elastic element is stretched to the greatest extent.

Isometric exercise provides a fixed amount of resistance based on the force output of the muscle. This only strengthens the muscle at the specific joint angle at which the isometric exercise occurs. In comparison, weight training strengthens the muscle throughout the entire range of motion of the joint.

A repetition (or "rep") is the act of lifting and lowering a weight once in a controlled manner. A "set" consists of several repetitions performed one after another with no break between them. The number of repetitions per set depends upon the aims of the individual performing the exercise. Sets with fewer reps are generally performed using more weight. Repetition tempo is also an important factor.

In one common method, weight training uses the principle of progressive overload, in which the muscles are overloaded by attempting to lift at least as much weight as they are capable of. They respond by growing larger and stronger.[6] This procedure is repeated with progressively heavier weights as the practitioner gains strength and endurance.

The benefits of weight training include greater muscular strength, improved muscle tone and appearance, increased endurance, enhanced bone density, and improved cardiovascular fitness.

Although weight training is similar to bodybuilding, they have quite different goals. Bodybuilders compete in bodybuilding competitions, so they train to maximize their muscular size and develop extremely low levels of body fat. In contrast, most weight trainers train to improve their strength and endurance while not giving special attention to reducing body fat below normal. Weight trainers tend to focus on compound exercises to build basic strength, whereas bodybuilders often use isolation exercises to visually separate their muscles, and to improve muscular symmetry. Pre-contest training for bodybuilders is different again, in that they attempt to retain as much muscular tissue as possible while undergoing severe dieting.

Most people think of dieting in terms of weight loss, but weight trainers can also adjust their diet to improve the results from their workouts. Adequate protein is required for building skeletal muscle. Various sources advise weight trainers to consume a high protein diet with anywhere from 0.6 to 1.5 g of protein per pound of body weight per day (1.4 to 3.3 g per kg).[15][16] Protein that is not needed for cell growth and repair nor consumed for energy is converted by the liver into fat, which is then stored in the body. Some people believe that a high protein diet entails risk of kidney damage, but studies have shown that kidney problems only occur in people with previous kidney disease.[17] A light balanced meal consumed prior to the workout (usually one to two hours beforehand) ensures that adequate energy and amino acids are available to perform the intense bout of exercise. Water is consumed throughout the course of the workout to prevent poor performance due to dehydration.[18] A protein shake is often consumed immediately following the workout, because both protein uptake and protein usage are increased at this time.[19] Glucose (or another simple sugar) is often consumed as well since this quickly replenishes any glycogen lost during the exercise period (see Gainer). Some weight trainers also take supplements (such as creatine) to aid muscle growth. However, the effectiveness of some products is disputed and others are potentially harmful.

Very few women are able to develop large muscles regardless of the program they follow; they simply lack the testosterone required to achieve this.[20] Normally the most that can be achieved is a look similar to that of a fitness model. Muscle is denser than fat, so someone who builds muscle while keeping the same body weight will look slimmer.[21] The results obtained by female bodybuilders are extremely atypical: they are self-selected for their genetic ability to build muscle,[citation needed] perform enormous amounts of exercise, their musculature is exaggerated by very low body fat and like many male bodybuilders their results may be enhanced by anabolic steroids.[22] Unless a woman dedicates her life to bodybuilding, she will not achieve the same results as a professional female bodybuilder.

Yes, but not via the low weight/high repetition approach that is usually used. Five minutes of crunches will expend only a small fraction of the energy used up in five minutes of running, because the abdominal muscles are so much smaller than the leg muscles.[25] Instead, high weight/low rep exercises can be used to maintain (and possibly even increase) the body's muscle mass while dieting. This helps to prevent the metabolic slowdown that otherwise often limits the effect of dieting and causes post-diet weight gain.