What precautions should I take when doing biceps curls?

Keeping the arm in a mechanically correct position during biceps curls fatigues the biceps muscles more quickly and with lighter weight. However, pushing past fatigue in order to reach a predetermined number of repetitions or lift heavier weight, the elbow compensates by rocking forward and back. When the elbow moves back, the head of the arm bone at the shoulder joint moves forward, often pulling the shoulder blade with it or stressing the tissues in the front of the shoulder. Over time this can create a host of mechanical problems in the shoulder joint. Biceps fatigue during curls is good pain because it indicates that the muscle is being stimulated to strengthen and grow. This is what we are shooting for when performing strengthening exercises. We want muscle stimulation and therefore improved strength and control of the bone or joint in question. In the biceps curl example, ignoring this fatigue to squeeze out a few more reps or allow you to lift more weight can cause shoulder joint problems. Become comfortable with and even rejoice in the fact that the muscle you are targeting is fatiguing. It is better to strengthen the muscle group incrementally rather than compensate your form -- and your healing process -- to squeeze out a few more repetitions. This is where bad pain comes in.