There's no sense in trying to lift a big amount of weight if you shorten your limbs in the process. Although many of their claims are unsubstantiated, such substances can be marketed without the FDA review of safety and effectiveness. Although some supplements may confer beneficial effects, most are associated with various adverse side-effects. You should remain skeptical when considering nutritional supplement use. Sometimes you concentrate so much on doing it correctly that you forget to let your body do its natural things, like breathing.
Proper breathing is very important.
Exhale during the exertion stage of each repetition and inhale during the return stroke. Never hold your breath, holding your breath can raise your blood pressure and, if you hold it long enough, cause fainting. Always use collars on the bars when you're working without a spotter. During a lift, the bar may begin to lean imperceptibly toward the weaker side of the body. Use collars if you don't want a red face or something more serious.