The incline biceps curl with supination is one of the best exercises for the biceps muscle mid-range development. The reason for this is that it is the only exercise that allows you to work the biceps in its two actions: elbow joint flexion and supination. Both of these actions are executed against the pull of gravity.
When you execute a biceps curl using very heavy weights, it is impossible to initiate the exercise with your arms held straight. However, heavy weights are necessary to produce maximum intensity for strength, mass and biceps peaking. Because of this, you should begin the exercise with your elbows slightly flexed as usually seen in the incline or standing biceps curl with supination, preacher curls, concentration curls, low pulley curls, and on most biceps curls machines. These are very effective exercises, but do not do them to the exclusion of straight-arm exercises or you will produce excessive shortening of the muscles.
The incline dumbbell curl can also be done using a supinated or neutral grip. Both of these grips are effective for development of the elbow joint flexors, and the biceps in particular. Most effective, however, is the incline dumbbell curl with supination to work the biceps in its two major actions.
