Weight training is a form of exercise for developing the strength and size of skeletal muscles. It is a common type of resistance training, which is one form of strength training. Properly performed, weight training can provide significant functional benefits and improvement in overall health and well-being.
In one common training method, the technique involves lifting progressively increasing amounts of weight, and uses a variety of exercises and types of equipment to target specific muscle groups. Weight training is primarily an anaerobic activity, although some proponents have adapted it to provide the benefits of aerobic exercise.
Weight training differs from bodybuilding, weightlifting, and powerlifting, which are sports rather than forms of exercise. Weight training, however, is often part of their training regimen.
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 performed using more weight. Repetition tempo is also an important factor.
According to popular theory:
Sets of one to five repetitions primarily develop strength, with less impact on muscle size and none on endurance.
Sets of six to twelve repetitions develop a balance of strength, muscle size and endurance.
Sets of thirteen to twenty repetitions develop endurance, with some increases to muscle size and limited impact on strength.
- Sets of more than twenty 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. The duration of these breaks determines which energy system the body utilizes: for example, performing a series of exercises with little or no rest between them is referred to as "circuit training", and the body will draw most of its energy from the aerobic energy system (as opposed to the ATP-CP or glycogen systems).
It has been shown that for beginners multiple-set training offers minimal benefits over single set training with respect to either strength gain or muscle mass increase, but for the experienced athlete multiple-set systems are required for optimal progress.
Training to achieve different performance goals (from "Supertraining" by Dr. M. C. Siff)
|Load (% of 1RM)
|Reps per set
|Sets per exercise
|Rest between sets (mins)
|Duration (seconds per set)
|Speed per rep (% of max)
|Training sessions per week
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."
Types of Exercises
Isotonic, isometric and plyometric exercises
These terms combine the prefix "iso" (meaning "same") with "tonic" (strength) and "metric" (distance). In "isotonic" exercises the force applied to the muscle does not change, and in "isometric" exercises the length of the muscle does not change.
Weight training is primarily an isotonic form of exercise, because the muscles are used to push or pull weighted objects. 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. However, some exercises are not strictly isotonic because the force on the muscle varies as the joint moves through its range of motion, even though the force of the exercise remains constant.
Some forms of weight training use isometric contractions to further stress the muscles after or during a period of isotonic exercise. In this case the muscles flex and hold a stationary position, and no movement of a load takes place.
Another form of training that often uses weights has a different goal. Plyometric exercises exploit the stretch-shortening cycle of muscles to enhance the myotatic (stretch) reflex. This involves rapid alternation of lengthening and shortening of muscle fibers against a resistance. The resistance involved is often a weighted object such as a medicine ball, but can also be the body itself as in jumping exercises. Plyometrics is used to develop explosive speed, and focuses on power instead of maximal strength, and may be used to improve the effectiveness of a boxer's punch, for example, or to increase the vertical jumping ability of a basketball player.
Isolation exercises versus 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. The other muscle groups are only minimally involved—they just help the individual maintain a stable posture—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.
The type of exercise performed also depends on the individual's goals. Those who seek to increase their performance in sports would focus mostly on compound exercises, with isolation exercises being used to strengthen just those muscles that are holding the athlete back. Similarly, a powerlifter would focus on the specific compound exercises that are performed at powerlifting competitions. However, those who seek to improve the look of their body without necessarily maximising their strength gains (including bodybuilders) would put more of an emphasis on isolation exercises.
Free weights versus 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 stabiliser muscles. It is often argued that free weight exercises are superior for precisely this reason. As exercise machines can go some way toward preventing poor form, they are somewhat safer than free weights for novice trainees. 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. However, most athletes, bodybuilders and serious fitness enthusiasts prefer to use compound free weight exercises to gain functional strength.
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 weight 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.
Aerobic exercise versus anaerobic exercise
Strength training exercise is primarily anaerobic. 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. 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. 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"), in order 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. 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.