Safety for Weight training

Weight training is a safe form of exercise when the movements are slow, controlled, and carefully defined. However, as with any form of exercise, improper execution and the failure to take appropriate precautions can result in injury.

Maintaining proper form
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 and to ensure training success, weight training exercises must be performed correctly. Standing exercises are performed in a completely erect posture, as though one's back were pressed to a wall, and sitting exercises are performed without slouching. Weights are not lifted with a jerk (which makes the exercise easier, but overstresses muscles and joints). Rather, trainers recommend that the positive phase of the lift take three seconds (counting "one-and-a, two-and-a, three-and-a"), followed by a one second pause and three seconds for the negative phase (lowering the weight).

Stretching and warm-up
The cross trainer 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.

Breathing
Breathing shallowly or holding one's breath while working out limits the oxygen supply to the muscles and the brain, decreasing performance and, under extreme stress, risking a black-out or a stroke by aneurysm. Weight trainers are advised to conscientiously "exhale on effort" and to inhale when lowering the weight. This technique ensures that the trainer breathes through the most difficult part of the exercise, where one would reflexively hold one's breath.

Hydration
As with other sports, weight trainers should avoid dehydration throughout the workout by drinking plenty of water, even while not thirsty; thirst is a sign that the body is already dehydrated. Sportspeople are advised to drink about 7 imperial fluid ounces (2.0 dl) every 15 minutes while exercising, and about 80 imperial fluid ounces (2.3 l) throughout the day. Under most circumstances, sports drinks do not offer a physiological benefit over water during weight training.
Insufficient hydration may cause lethargy, soreness or muscle cramps. The urine of well-hydrated persons should be nearly colorless, while an intense yellow color is normally a sign of insufficient hydration.

Straps and belts
A lifting belt is sometimes worn to help support the lower back.
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 is safe. In addition, the stabilizer 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 some of the weight directly to the wrist instead of through 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, and can place potentially harmful stress on the bones of the wrist.

Avoiding pain
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. Muscle fatigue and soreness, contrary to popular belief, is not caused by lactate buildup but by the acid byproduct generated by glycolosis metabolism and the corresponding drop in pH. 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.