Just like the bottom position of the military press, the bottom position of a curl is very stressful to the shoulder. I recommend hitching at the waist and leaning slightly forward then extending your hips and cheating the weight the first couple inches out of the bottom.This doesnt mean you heave the weight up and get sloppy. Quite the contrary. Just use the momentum to initiate the movement and then keep maximal tension on the biceps throughout by squeezing and contracting them as hard as you can. On the eccentric actively contract your triceps by imagining doing a pushdown.Using this cheat technique can extend the life of your shoulders and elbows greatly.