A gym environment where various forms of strength training are being practiced. Identified from left to right, the exercises are: overhead presses, battle ropes, planking, and kettlebell raises.
A gym environment where various forms of strength training are being practiced. Identified from left to right, the exercises are: overhead presses, battle ropes, planking, and kettlebell raises.

Strength training or resistance training involves the performance of physical exercises that are designed to improve strength and endurance. It is often associated with the lifting of weights. It can also incorporate a variety of training techniques such as bodyweight exercises, isometrics, and plyometrics.[1]

Training works by progressively increasing the force output of the muscles and uses a variety of exercises and types of equipment. Strength training is primarily an anaerobic activity, although circuit training also is a form of aerobic exercise.

Strength training can increase muscle, tendon, and ligament strength as well as bone density, metabolism, and the lactate threshold; improve joint and cardiac function; and reduce the risk of injury in athletes and the elderly. For many sports and physical activities, strength training is central or is used as part of their training regimen.

Principles and training methods

The basic principles of strength training involve repeated overloading of a group of muscles, typically by contracting the muscles under heavy resistance and returning to the start position for several repetitions until failure.[2] The basic method of resistance training uses the principle of progressive overload, in which the muscles are overloaded by working against as high resistance as they are capable of. They respond by growing larger and stronger.[3] Beginning strength-trainers are in the process of training the neurological aspects of strength, the ability of the brain to generate a rate of neuronal action potentials that will produce a muscular contraction that is close to the maximum of the muscle's potential.[4][better source needed]

Maintaining Proper Form

A dumbbell half-squat.[5]

Strength training also requires the use of proper or 'good form', performing the movements with the appropriate muscle group, and not transferring the weight to different body parts in order to move greater weight (called 'cheating'). Failure to use good form during a training set can result in injury or a failure to meet training goals. If the desired muscle group is not challenged sufficiently, the threshold of overload is never reached and the muscle does not gain in strength. At a particularly advanced level; however, "cheating" can be used to break through strength plateaus and encourage neurological and muscular adaptation.[6]

Maintaining proper form is one of the many steps in order to perfectly perform a certain technique. Correct form in weight training improves strength, muscle tone, and maintaining a healthy weight. Proper form will prevent any strains or fractures.[7]

Stretching and warm-up

Weight trainers spend time warming up their muscles before starting a workout. It is common to stretch the entire body to increase overall flexibility; many people stretch just the area being worked that day. It has been observed that static stretching can increase the risk of injury due to its analgesic effect and cellular damage caused by it.[8] A proper warm-up routine, however, has shown to be effective in minimizing the chances of injury, especially if they are done with the same movements performed in the weight lifting exercise.[9] When properly warmed up the lifter will have more strength and stamina since the blood has begun to flow to the muscle groups.[10]


In weight training, as with most forms of exercise, there is a tendency for the breathing pattern to deepen. This helps to meet increased oxygen requirements. Holding the breath or breathing shallowly is avoided because it may lead to a lack of oxygen, passing out, or an increase in blood pressure. Generally, the recommended breathing technique is to inhale when lowering the weight (the eccentric portion) and exhale when lifting the weight (the concentric portion). However, the reverse, inhaling when lifting and exhaling when lowering, may also be recommended. Some researchers state that there is little difference between the two techniques in terms of their influence on heart rate and blood pressure.[11]

Intensity, volume, and frequency

Three important variables of strength training are intensity, volume, and frequency. Intensity is the amount of work required to achieve the activity and is often measured by the percentage of an individual's one-repetition maximum (1RM).[citation needed] The intensity limits the number of repetitions that can be carried out in one set, and is correlated with the repetition ranges chosen, traditionally divided as follows:[12]

Volume refers to the total number of muscles worked, exercises, sets, and reps, either during a single session or measured over a longer period. Frequency refers to how many training sessions are performed per week.[13][better source needed] A training frequency of two times per week has greater effect on muscle size than once per week. Whether training a muscle group three times per week is superior to a twice-per-week protocol remains to be determined.[14] Training volume has more effect on muscle strength than training frequency.[15]

A common training strategy is to set the volume and frequency the same each week (e.g. training 3 times per week, with 2 sets of 12 reps each workout), and steadily increase the resistance on a weekly basis. However, to maximize progress to specific goals, individual programs may require different manipulations, such as decreasing the resistance, and increase volume or frequency.[16]


A meta-analysis found that periodized training yields better strength improvements than non-periodized training.[17] Making program alterations on a daily basis (daily undulating periodization) has similar effect to other periodization models.[18]

Training Splits

A training split refers to how the trainee divides and schedules their training volume, or in other words which muscles are trained on a given day over a period of time (usually a week). Popular training splits include full body, upper/lower, push/pull/legs, and the "bro" split. Some training programs may alternate splits weekly.[19][better source needed]


Commonly used equipment for resistance training include free weights—including dumbbells, barbells, and kettlebellsweight machines, and resistance bands.[20]

Resistance can also be generated by inertia in flywheel training instead of by gravity from weights, facilitating variable resistance throughout the range of motion and eccentric overload.[21][22]

Some bodyweight exercises do not require any equipment, and others may be performed with equipment such as suspension trainers or pull-up bars.[23][24]

Aerobic exercise versus anaerobic exercise

See also: Anaerobic exercise

Strength training exercise is primarily anaerobic.[25] Even while training at a lower intensity (training loads of ~20-RM), anaerobic glycolysis is still the major source of power, although aerobic metabolism makes a small contribution.[26] Weight training is commonly perceived as anaerobic exercise, because one of the more common goals is to increase strength by lifting heavy weights. Other goals such as rehabilitation, weight loss, body shaping, and bodybuilding often use lower weights, adding aerobic character to the exercise.

Except in the extremes, a muscle will fire fibres of both the aerobic or anaerobic types on any given exercise, in varying ratio depending on the load on the intensity of the contraction.[25] This is known as the energy system continuum. At higher loads, the muscle will recruit all muscle fibres possible, both anaerobic ("fast-twitch") and aerobic ("slow-twitch"), to generate the most force. However, at maximum load, the anaerobic processes contract so forcefully that the aerobic fibers are completely shut out, and all work is done by the anaerobic processes. Because the anaerobic muscle fibre uses its fuel faster than the blood and intracellular restorative cycles can resupply it, the maximum number of repetitions is limited.[27] In the aerobic regime, the blood and intracellular processes can maintain a supply of fuel and oxygen, and continual repetition of the motion will not cause the muscle to fail.

Circuit weight training is a form of exercise that uses a number of weight training exercise sets separated by short intervals. The cardiovascular effort to recover from each set serves a function similar to an aerobic exercise, but this is not the same as saying that a weight training set is itself an aerobic process.

Strength training is typically associated with the production of lactate, which is a limiting factor of exercise performance. Regular endurance exercise leads to adaptations in skeletal muscle which can prevent lactate levels from rising during strength training. This is mediated via activation of PGC-1alpha which alter the LDH (lactate dehydrogenase) isoenzyme complex composition and decreases the activity of the lactate generating enzyme LDHA, while increasing the activity of the lactate metabolizing enzyme LDHB.[28]

Nutrition and supplementation

Main article: Sports nutrition

A 2018 systematic review found that supplementation of protein in the diet of healthy adults increased the size and strength of muscles during prolonged resistance exercise training; protein intakes of greater than 1.6 g/kg/day did not additionally increase fat-free mass or muscle size or strength.[29] It is not known how much carbohydrate is necessary to maximize muscle hypertrophy. Strength adaptations may not be hindered by a low-carbohydrate diet.[30]

A light, balanced meal prior to the workout (usually one to two hours beforehand) ensures that adequate energy and amino acids are available for the intense bout of exercise. The type of nutrients consumed affects the response of the body, and nutrient timing whereby protein and carbohydrates are consumed prior to and after workout has a beneficial impact on muscle growth.[31] Water is consumed throughout the course of the workout to prevent poor performance due to dehydration. A protein shake is often consumed immediately[32] following the workout. Glucose (or another simple sugar) is often consumed as well since this quickly replenishes any glycogen lost during the exercise period. If consuming recovery drink after a workout, to maximize muscle protein anabolism, it is suggested that the recovery drink contain glucose (dextrose), protein (usually whey) hydrolysate containing mainly dipeptides and tripeptides, and leucine.[33]

Some weight trainers also take ergogenic aids such as creatine[34] or anabolic steroids to aid muscle growth.[35]


As with other sports, weight trainers should avoid dehydration throughout the workout by drinking sufficient water. This is particularly true in hot environments, or for those older than 65.[36][37][38][39][40]

Some athletic trainers advise athletes to drink about 7 imperial fluid ounces (200 mL) every 15 minutes while exercising, and about 80 imperial fluid ounces (2.3 L) throughout the day.[41]

However, a much more accurate determination of how much fluid is necessary can be made by performing appropriate weight measurements before and after a typical exercise session, to determine how much fluid is lost during the workout. The greatest source of fluid loss during exercise is through perspiration, but as long as fluid intake is roughly equivalent to the rate of perspiration, hydration levels will be maintained.[38]

Under most circumstances, sports drinks do not offer a physiological benefit over water during weight training.[42]

Insufficient hydration may cause lethargy, soreness or muscle cramps.[43] The urine of well-hydrated persons should be nearly colorless, while an intense yellow color is normally a sign of insufficient hydration.[43]


The effects of strength training include greater muscular strength, improved muscle tone and appearance, increased endurance, cardiovascular health, and enhanced bone density.[44]

Bones, joints, frailty, posture and in people at risk

Strength training also provides functional benefits. Stronger muscles improve posture,[vague] provide better support for joints,[vague] and reduce the risk of injury from everyday activities.[45][46]

Progressive resistance training may improve function, quality of life and reduce pain in people at risk of fracture, with rare adverse effects[47] Weight-bearing exercise also helps to prevent osteoporosis and to improve bone strength in those with osteoporosis.[48] For many people in rehabilitation or with an acquired disability, such as following stroke or orthopaedic surgery, strength training for weak muscles is a key factor to optimise recovery.[49]

Mortality, longevity, muscle and body composition

A scientific review indicates that, based on mostly observational studies, strength training appears to be associated with a "10–17% lower risk of all-cause mortality, cardiovascular disease (CVD), total cancer, diabetes and lung cancer".[50] Two key outcomes of strength training are muscle hypertrophy and muscular strength gain which are associated with reduced all-cause mortality.[51]

Strength training causes endocrine responses that could have positive effects.[52] It also reduces blood pressure (SBP and DBP)[53][54] and alters body composition, reducing body fat percentage, body fat mass and visceral fat,[55] which is usually beneficial as obesity predisposes towards several chronic diseases and e.g. body fat distribution is one predictor of insulin resistance and related complications.[56]

Neurobiological effects

Strength training also leads to various beneficial neurobiological effects – likely including functional brain changes, lower white matter atrophy,[57] neuroplasticity[58] (including some degree of BDNF expression),[59] and white matter-related structural and functional changes in neuroanatomy.[60] Although resistance training has been less studied for its effect on depression than aerobic exercise, it has shown benefits compared to no intervention.[61]

Lipid and inflammatory outcomes

Moreover, it also promotes decreases in total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL), and C-reactive protein (CRP) as well as increases in high-density lipoprotein (HDL) and adiponectin concentrations.[62]

Sports performance

Stronger muscles improve performance in a variety of sports. Sport-specific training routines are used by many competitors. These often specify that the speed of muscle contraction during weight training should be the same as that of the particular sport.[63] Strength training can substantially prevent sports injuries,[64] increase jump height and improve change of direction.


See also: History of physical training and fitness

Arthur Saxon performing a Two Hands Anyhow with an early kettlebell and plate-loaded barbell
Arthur Saxon performing a Two Hands Anyhow with an early kettlebell and plate-loaded barbell

The genealogy of lifting can be traced back to the beginning of recorded history[65] where humanity's fascination with physical abilities can be found among numerous ancient writings. In many prehistoric tribes, they would have a big rock they would try to lift, and the first one to lift it would inscribe their name into the stone. Such rocks have been found in Greek and Scottish castles.[66] 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.

Ancient Greek sculptures also depict lifting feats. The weights were generally stones, but later gave way to dumbbells. The dumbbell was joined by the barbell in the later 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.[67]

Weightlifting was first introduced in the Olympics in the 1896 Athens Olympic Games as a part of track and field, and was officially recognized as its own event in 1914.[68]

The 1960s saw the gradual introduction of exercise machines into the still-rare strength training gyms of the time. Weight training became increasingly popular in the 1970s, 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 weight training; currently, nearly one in five U.S. women engage in weight training on a regular basis.[69]


Sex differences

Men and women have similar reactions to resistance training with comparable effect sizes for hypertrophy and lower body strength, although some studies have found that women experience a greater relative increase in upper-body strength. Because of their greater starting strength and muscle mass, absolute gains are higher in men.[70] In older adults, a systematic review found that women experienced a larger increase in lower-body strength.[71]

Safety concerns related to children

Orthopaedic specialists used to recommend that children avoid weight training because the growth plates on their bones might be at risk. The very rare reports of growth plate fractures in children who trained with weights occurred as a result of inadequate supervision, improper form or excess weight, and there have been no reports of injuries to growth plates in youth training programs that followed established guidelines.[72][73] The position of the National Strength and Conditioning Association is that strength training is safe for children if properly designed and supervised.[74] Younger children are at greater risk of injury than adults if they drop a weight on themselves or perform an exercise incorrectly; further, they may lack understanding of, or ignore the safety precautions around weight training equipment. As a result, supervision of minors is considered vital to ensuring the safety of any youth engaging in strength training.[72][73]

Older adults

Aging is associated with a decrease in muscle mass and strength.[75][76][77] Resistance training can mitigate this effect,[75][77] and even the oldest old (those above age 85) can increase their muscle mass with a resistance training program, although to a lesser degree than younger individuals.[75] With more strength older adults have better health, better quality of life, better physical function[77] and fewer falls.[77] Resistance training can improve physical functioning in older people, including the performance of activities of daily living.[77][75] Resistance training programs are safe for older adults, can be adapted for mobility and disability limitations, and may be used in assisted living settings.[75]


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