Safety

An individual performing a dumbbell squat.

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".

A lifting belt is sometimes worn to help support the lower back.

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 working through the discomfort expected from such vigorous effort, rather than to willfully ignore extreme pain, which may indicate serious soft tissue injuries.

Discomfort can arise from other factors. Individuals who perform large numbers of repetitions, sets and exercises for each muscle group may experience a burning sensation in their muscles, which, contrary to popular belief, is not caused by lactic acid build-up. These individuals may also experience a swelling sensation in their muscles from increased blood flow (the "pump"). True muscle fatigue is experienced as a marked and uncontrollable loss of strength in a muscle, arising from the nervous system (motor unit) rather than from the muscle fibers themselves. Extreme neural fatigue can be experienced as temporary muscle failure. Some weight training programs actively seek temporary muscle failure; evidence to support this type of training is mixed at best. Irrespective of their program, however, most athletes engaged in high-intensity weight training will experience muscle failure from time to time.

Beginners are advised to build up slowly to a weight training programme. 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. This can also help to minimise delayed onset muscle soreness. A sudden start to an intense program can cause significant muscular soreness. Unexercised muscles contain cross-linkages that are torn during intense exercise.

The Cross Trainer exercise machine can be used to warm up muscles in both the upper and lower body.

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 two to four 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, which can result in injury if the weight drops onto the lifter, are normally performed inside a squat cage or in the presence of one or more spotters, who can safely re-rack the barbell if the weight trainer is unable to do so.

Anyone beginning an intensive physical training programme is typically advised to consult a physician, because of possible undetected heart or other conditions for which such activity is contraindicated.

Using a wrist strap.

There have been mixed reviews regarding the use of weightlifting belts and other devices, such as lifting straps. Critics claim that they allow the lifter to use more weight than they should. In addition, the stabiliser muscles in the lower back and gripping muscles in the forearms receive less benefit from the exercises.

Wrist straps (also known as cow ties or lifting straps) are sometimes used to assist in gripping very heavy weights. The straps wrap around the wrist and tuck around the bar or weight being lifted, transferring the mass of the weight to the wrist rather than the fingers. They are particularly useful for the deadlift. Some lifters avoid using wrist straps in order to develop their grip strength. Wrist straps can allow a lifter initially to use more weight than they might be able to handle safely for an entire set, but can place potentially harmful stress on the bones of the wrist.