Science Fair Project Encyclopedia
Weight training can be the most effective technique for developing the strength and size of skeletal muscles. It provides functional benefits, often results in a more attractive physique, and may improve overall health and well-being.
In one common training method, the technique involves progressively lifting increasing amounts of weight, and uses a variety of exercises and types of equipment to target specific muscle groups. Weight training can be either aerobic or anaerobic, depending on intensity and duration. It is a common form of resistance training, which is one form of strength training.
Main article: History of strength training
Hippocrates eloquently explained the principle behind weight training when he wrote "that which is used develops, and that which is not used wastes away." 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.
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 we use 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. Weight 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 weight training, influenced by programs like Body for Life.
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 of 1 to 5 repetitions primarily develop strength, with less impact on muscle size and none on endurance.
- Sets of 6 to 12 repetitions develop a balance of strength, muscle size and endurance.
- Sets of 13 to 20 repetitions develop muscle size, and particularly endurance, with less impact on strength.
- Sets of more than 20 repetitions are considered to be an aerobic exercise.
Individuals typically perform one to six sets per exercise, and one to three exercises per muscle group, with short breaks between each set. Weights for each exercise should be chosen so that the desired number of repetitions can just be achieved. Each exercise should be performed according to its description; otherwise injury may result. This is known as "good form."
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 . This procedure is repeated with progressively heavier weights as the practitioner gains strength and endurance.
However, performing exercises at the absolute limit of one's strength (so-called "one rep max" lifts) is considered too risky for all but the most experienced practitioners, or novices under expert supervision. Moreover, most individuals wish to develop a combination of strength, endurance and muscle size. One repetition sets are not well suited to these aims. Practitioners therefore lift somewhat smaller (sub-maximal) weights, with more repetitions, to fatigue the muscle—and all fibres within that muscle—as required by the progressive overload principle.
Each exercise is continued to the point of momentary muscular failure. Contrary to widespread belief, this is not the point at which the individual thinks they cannot complete any more repetitions, but rather the first repetition that fails due to inadequate muscular strength. "Training to failure" is, however, a controversial topic. The proponents of High Intensity Training—Mike Mentzer, Arthur Jones and Ellington Darden—advise training to failure on every set. But other experts believe that this will lead to overtraining, and suggest training to failure only on the last set of an exercise .
Weight training has the potential to be the most effective form of strength training because exercises can be chosen, and weights precisely adjusted to safely exhaust each individual muscle group after the specific numbers of sets and repetitions that have been found to be the most effective for the individual. Other strength training exercises lack the flexibility and precision that weights offer, and often cannot be safely taken to the point of momentary muscular failure.
Weight training creates muscle growth by causing microtrauma to the muscles. Muscles grow during the rest period following a workout by repairs to these areas of muscle, making them stronger than before. Weight training programs should therefore allow the muscles time to repair and grow, otherwise overtraining can occur. Muscle growth is normally completed within 36 to 96 hours, depending upon the intensity of the workout  . Novices commonly work out every other day, often scheduling workouts on Mondays, Wednesdays and Fridays. As weight trainers grow fitter and stronger, it takes longer and more intense workouts to fully challenge their muscles. More advanced practitioners may exercise specific muscle groups only every three or four days.
One solution to scheduling workouts around these needs is to split one's routine between several workouts, by exercising certain muscle groups on one day and the remainder on another. One common two-day split is the upper body – lower body split. Another is the front – back split, in which the pectorals, triceps and quadriceps are exercised on one day, and the lats, biceps and hamstrings on another. There are also three-day and four-day splits. By targeting different muscle groups, workouts can be scheduled more frequently than would otherwise be possible.
Many people take up weight training in the belief that it will improve their physical attractiveness. Men can develop substantial muscles; women lack the testosterone to do this, but they can develop a firm, "toned" physique. The body's basal metabolic rate increases with increases in muscle mass, which promotes long-term fat loss and helps dieters avoid yo-yo dieting . Moreover, intense workouts elevate the metabolism for several hours following the workout, which also promotes fat loss . (Although weight-training alone will not reduce levels of bodyfat without the help of a suitable diet.)
Weight training also provides functional benefits. Stronger muscles improve posture, provide better support for joints and reduce the risk of injury from everyday activities. Older people who take up weight training can reverse the loss of muscle tissue that normally accompanies ageing, and by doing so become less frail . They may be able to avoid some types of physical disability. Heavy, weight-bearing exercise also helps to prevent osteoporosis .
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.
One side-effect of intense exercise is that it increases levels of dopamine, serotonin and norepinephrine, which can help to improve mood and counter feelings of depression  (although in some cases this can lead to an almost addiction-like desire to exercise). Weight training also relaxes tense muscles by working them through their full range of motion, which helps to reduce levels of stress .
Is weight training the same as bodybuilding?
Weight training is often confused with bodybuilding, but they are actually quite different. 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 maintaining a normal level of body fat. 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.
However, the bodybuilding community has been the source of many of weight training's principles, techniques, vocabulary and customs. One particularly worrying trend has been the spread of anabolic steroid use into neighbourhood gyms.
Is nutrition relevant for weight trainers?
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. There is ongoing debate about the issue, but various sources advise weight trainers to consume a high protein diet with anywhere from 0.6 to 1.5g of protein per pound of body weight per day (1.4–3.3g per kg)  . However, many medical professionals believe that consuming more protein than the Recommended Dietary Allowance provides no benefits, and that the excess is merely burnt for energy or excreted.
A light meal consumed one to two hours prior to the workout ensures that enough glucose is available for the muscles. Water is consumed throughout the course of the workout to prevent poor performance due to dehydration . A protein shake is often consumed immediately following the workout, because both protein uptake and protein usage are increased at this time . Some weight trainers also take creatine supplements to improve their performance during workouts.
Do women who train with weights look "bulky"?
Very few women can develop large muscles, no matter what program they follow; they simply lack the testosterone required to achieve this . 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.
The results obtained by female bodybuilders are extremely atypical: they are self-selected for their genetic ability to build muscle, they perform enormous amounts of exercise, and they often take anabolic steroids, or other supplements with similar effects. The muscular look is exaggerated by their very low levels of body fat.
Are light, high-repetition exercises effective for toning muscles?
Some weight trainers perform light, high-repetition exercises in an attempt to "tone" their muscles without increasing their size. This comes from misunderstanding the meaning of the word "tone." A toned physique is one that combines reasonable muscular size with moderate levels of body fat. Muscle tone is the constant low-frequency contractions that occur in all muscles all the time, even at "rest"; the constant slight tension in torso muscles allows one to maintain a good posture. High-repetition exercises will not improve either of these. Even as aerobic exercises they will have limited benefits, since aerobic exercise is most effective when it engages the whole body.
Is weight training safe for children?
Orthopedic specialists used to recommend that children avoid weight training because the growth plates on their bones might be at risk, but recent studies have shown that this concern is unfounded. 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. "Growth plate injuries have not occurred in any youth strength training study that followed established training guidelines." The authors of DeLee & Drez's orthopaedic sports medicine, 2003 found similarly: "Review of the recent literature... ...reveals that there is no reason to prevent children from strength training in a well supervised, well-designed program." 8 This finding is in line with medical practitioners belief that young children must be supervised around weight training equipment. Like adults, they may be injured if a weight is dropped, or if they perform an exercise incorrectly. But, being children, they may also forget to follow the safety guidelines, or be tempted to act irresponsibly.
Weight training can be one of the safest forms of exercise, especially when the movements are slow, controlled, and carefully defined. However, as with any form of exercise, improper execution can result in injury. When the exercise becomes difficult towards the end of a set, there is a temptation to "cheat", i.e. to use poor form to recruit other muscle groups to assist the effort. This may shift the effort to weaker muscles that cannot handle the weight. For example, the squat and the deadlift are used to exercise the largest muscles in the body—the leg and buttock muscles—so they require substantial weight. Beginners are tempted to round their back while performing these exercises. This causes the weaker lower back muscles to support much of the weight, which can result in serious lower back injuries. To avoid such problems, weight training exercises must be performed correctly. Hence the saying: "train, don't strain".
An exercise should be halted if marked or sudden pain is felt, to prevent further injury. However, not all discomfort indicates injury. Weight training exercises are brief but very intense, and many people are unaccustomed to this level of effort. The expression "no pain, no gain" refers to the discomfort expected from such vigorous effort. It does NOT suggest ignoring the more severe pain that comes from injury.
Discomfort can arise from other factors. Individuals who perform large numbers of repetitions, sets and exercises for each muscle group may experience lactic acid buildup in their muscles. This is experienced as a burning sensation in the muscle, but it is perfectly harmless. These individuals may also experience a swelling sensation in their muscles from increased blood flow (the "pump"), which is also harmless.
Beginners are advised to build up slowly to a weight training program, ostensibly to minimise delayed onset muscle soreness. It is true that a sudden start to an intense program can cause significant muscular soreness. Unexercised muscles contain cross-linkages that are torn during intense exercise. A more important reason, though, is that untrained individuals may have some muscles that are comparatively stronger than others. An injury can result if, in a particular exercise, the primary muscle is stronger than its stabilising muscles. Building up slowly allows muscles time to develop appropriate strengths relative to each other.
Weight trainers commonly spend 5 to 20 minutes warming up their muscles with aerobic exercise before starting a workout. They also stretch muscles after they have been exercised. The exercises are performed at a steady pace, taking at least 2 to 4 seconds to lift and lower the weight, to avoid jerks that can damage muscles and joints.
Exercises where a barbell is held above the body, such as the squat or the bench press, are normally performed in the presence of one or more spotters, who can safely re-rack the barbell at the end of the set if the weight trainer is unable to do so.
Anyone beginning an intensive physical training program should consult a physician, because of possible undetected heart or other conditions for which such activity is contraindicated.
Types of exercises
Isometric exercises vs isotonic exercises vs isokinetic exercises
In isometric exercises the muscles flex and hold a stationary position. No movement of a load takes place, and the exercises require little in the way of equipment. An example of an isometric exercise is placing the palms of the hands against each other and pushing. Strength increases only occur at the angles the joints are held at during the exercise . Isometric exercises are primarily used in physiotherapy and injury rehabilitation because the intensity can be rapidly and precisely adjusted, which makes them very safe. They are now rarely used outside this context.
In isotonic exercises the muscles are used to push or pull a weight. Any object can be used for weight training, but dumbbells, barbells and other specialised equipment are normally used because they can be adjusted to specific weights, and are easily gripped. Elastic resistance bands are a cheap and portable alternative. Some exercises, such as the push-up, use the individual's bodyweight instead. Advanced practitioners often add weight to bodyweight exercises such as the crunch by, in this case, holding a dumbbell on their chest.
A third type of training, which is less common—except in sport-specific training or in rehabilitation—is isokinetic exercise. An exercise machine is used which registers the force applied to it by the user, and offers just that amount of resistance. (The rate of change of angle at the joints being utilised is kept constant.) This allows the user to exercise at the speed optimal for their needs, without the danger of being subjected to more weight than they can handle.
These terms combine the prefix "iso", meaning same, with "metric" (distance), "tonic" (strength) and "kinetic" (speed). In "isometric" exercises the length of the muscle does not change, in "isotonic" exercises the force applied to the muscle is relatively unchanged, and in "isokinetic" exercises the speed of movement is constant.
Isolation exercises vs compound exercises
An isolation exercise is one where the movement is restricted to one joint and one muscle group. For example, the leg extension is an isolation exercise for the quadriceps. No other muscle groups are involved, and movement occurs only around the knee joint.
Compound exercises work several muscle groups at once, and include movement around two or more joints. For example, in the leg press movement occurs around the hip, knee and ankle joints. This exercise is primarily used to develop the quadriceps, but it also involves the hamstrings, glutes and calves.
Compound exercises are generally similar to the ways that people naturally push, pull and lift objects, whereas isolation exercises often feel a little unnatural.
Each type of exercise has its uses. Compound exercises build the basic strength that is needed to perform everyday pushing, pulling and lifting activities. Isolation exercises are useful for "rounding out" a routine, by directly exercising muscle groups that cannot be fully exercised in the compound exercises.
Free weights vs exercise machines
Free weights are dumbbells and barbells. Unlike exercise machines, they do not constrain users to specific, fixed movements, and therefore require more effort from the individual's stabilizer muscles. It is often argued that free weights exercises are superior for precisely this reason. But because exercise machines largely prevent users from performing exercises with poor form, they are safer than free weights—particularly for beginners. Moreover, since users need not concentrate so much on maintaining good form, they can focus more on the effort they are putting into the exercise—which may lead to faster progress.
Some free weight exercises can be performed while sitting or lying on a Swiss ball. This makes it more difficult to maintain good form, which helps to exercise the deep torso muscles that are important for maintaining a good posture.
There are a number of exercise machines that are commonly found in neighbourhood gyms. The Smith machine is a barbell that is constrained to move only vertically upwards and downwards. The cable machine consists of two weight stacks separated by 2.5 metres, with cables running through adjustable pulleys (that can be fixed at any height) to various types of handles. There are also exercise-specific machines such as the leg press. A multigym includes a variety of exercise-specific mechanisms in one apparatus.
One limitation of many free weight exercises and exercise machines is that the muscle is working maximally against gravity during only a small portion of the lift. Some exercise-specific machines feature an oval cam (first introduced by Nautilus) which varies the resistance so that the resistance, and the muscle force required, remains constant throughout the full range of motion of the exercise.
Physical educators have long used various apparatus—including medicine balls, jump ropes, and Indian clubs—for specific training needs. While some of these have fallen into disuse, others have been shown to take good advantage of weight training principles. With many weight training regimens, the muscles are allowed to rest between repetitions while returning to the start position. The science of plyometrics rests on the finding that muscles respond especially well to being subjected to rapid alternation of lengthening and shortening while resistance is being continuously applied to them.
One application of the plyometric principle involves catching and tossing a medicine ball to an assistant while the exerciser lies on his back. The triceps and chest muscles are working both while they are lengthening (catch phase) and while contracting (toss phase). Plyometric exercises carry increased risk of injury, and should only be performed by well-conditioned individuals who are under supervision.
Plyometrics is used to develop explosive speed, and focuses on power instead of raw strength. Plyometrics may be used to, for example, improve the effectiveness of a boxer's punch, or increase the vertical jumping ability of a basketball player.
Aerobic exercise vs anaerobic exercise
Weight training at high intensity (using a weight towards the maximum the participant can lift for a given number of repetitions, or a lower weight and a sharp motion) is primarily anaerobic7, and at low intensity (low weight and slower, steady motion) is substantially aerobic.
Except in the extremes, a muscle will fire fibers of both the aerobic or anaerobic types on any given exercise, in varying ratio depending on the intensity of the contraction. At higher intensities, the lift requires more anaerobic (fast-twitch) fibers, and at maximum intensity will require no aerobic (slow-twitch) fibers. The anaerobic muscle fiber uses its fuel faster than the blood and intracellular restorative cycles can resupply it, limiting the maximum number of repetitions possible. 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.
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.
In a sense, all aerobic exercises are a form of weight training involving moving the weight of the body or another object in space.
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 not the same as saying that a weight training set is itself an aerobic process.
Exercises for specific muscle groups
Main article: Weight training exercises
Weight trainers commonly divide the body's individual muscles into ten major muscle groups. These do not include hip, neck and forearm muscles, which are rarely trained in isolation. The twenty most common exercises for these muscle groups are listed below.
The sequence shown below is one possible way to order the exercises. The large muscles of the lower body are normally trained before the smaller muscles of the upper body, because these first exercises require more mental and physical energy. The core muscles of the torso are trained before the shoulder and arm muscles that assist them. Exercises often alternate between "pushing" and "pulling" movements to allow their specific supporting muscles time to recover. The stabilising muscles in the waist should be trained last.
| Lower body
1. Quadriceps (front of legs)
Compound exercises for the quadriceps also involve the glutes (buttocks), hamstrings and calves.
2. Hamstrings (back of legs)
| Upper body
4. Pectorals (chest)
Compound exercises for the pectorals also involve the triceps and front deltoids.
5. Lats (upper back)
Compound exercises for the lats also involve the biceps and rear deltoids.
6. Deltoids (shoulders)
Compound exercises for the deltoids also involve the trapezius (neck) and arms.
| 7. Triceps (back of arms)
8. Biceps (front of arms)
9. Abdominals (belly)
Compound exercises for the abdominals also involve the hip flexors.
10. Lower back
Compound exercises for the lower back also involve the glutes.
A number of techniques have been developed to make weight training exercises more intense, and thereby potentially increase the rate of progress:
- Drop sets do not end at the point of momentary muscular failure, but continue with progressively lighter weights.
- Forced reps also occur after momentary muscular failure. An assistant provides just enough help to allow further repetitions to be completed.
- Supersets combine two or more exercises for different muscle groups. The exercises are performed back to back, with no rest period between them.
- Partial reps are performed with heavier weights. Only the easiest part of the repetition is attempted.
- Negatives are performed with much heavier weights. Assistants lift the weight, and then the weight trainer attempts to resist its downward progress. Alternatively, an individual can use an exercise machine for negatives by lifting the weight with both arms or legs, and then lowering it with only one.
- Super slow repetitions are performed with lighter weights. The lifting and lowering phases of each repetition take 10 seconds or more.
- Pre-exhaustion combines an isolation exercise with a compound exercise for the same muscle group. The isolation exercise first exhausts the muscle group, and then the compound exercise uses the muscle groups's supporting muscles to push it further than would otherwise be possible.
- Wrist straps (lifting straps) are sometimes used to assist in gripping very heavy weights. They are particularly useful for the deadlift.
Many of the most useful books about weight training contain the word "bodybuilding" in the title, but they should not be overlooked just for this reason. Weight trainers who are not interested in bodybuilding can ignore the material devoted to contest preparation, and still obtain much valuable information.
- Darden, Ellington (2004). The New High Intensity Training. Rodale Books. ISBN 1594860009.
- Delavier, Frederic (2001). Strength Training Anatomy. Human Kinetics Publishers. ISBN 0736041850.
- Hatfield, Frederick (1993). Hardcore Bodybuilding: A Scientific Approach. McGraw-Hill. ISBN 0809237288.
- Powers, Scott and Edward Howley (2003), Exercise Physiology. McGraw Hill. ISBN 0072557281.
- Schoenfeld Brad (2002). Sculpting Her Body Perfect. Human Kinetics Publishers. ISBN 0736044698.
- Schwarzenegger, Arnold (1999). The New Encyclopedia of Modern Bodybuilding. Simon & Schuster. ISBN 0684857219.
- Cahill, et al (December 1997). The Clinical Importance of the Anaerobic Energy System and Its Assessment in Human Performance. American Journal of Sports Medicine Vol 25, Number 6.
- DeLee, J. MD and Drez, D. MD, Eds. (2003). DeLee & Drez's orthopaedic sports medicine; principles and practice. Vol 1&2 ISBN 0-7216-8845-4
- Exercise and muscle directory
- A beginners guide to weight training
- Women-friendly weight training advice
- In-depth weight training articles
- A history of barbells and dumbbells
- A short summary of kettlebell training in comparison to dumbbells
- Discussion of aerobic and anaerobic muscle fibers
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