Several variations on the biceps curl transfer some of the load from the biceps to other flexors of the elbow, thus enabling a person to use bigger weights without causing an injury. One group of variations involves postures that hold the elbows in front of the trunk, shortening the biceps and forcing the brachialis to do more work. Variations on this theme include the preacher curl where the elbows rest upon a sloped bench, the concentration curl where the elbow is braced against the inside of the knee, and the prone incline curl performed lying prone on an inclined bench, where the force of gravity holds the upper arms in front of the trunk. There is also spider curls which uses the preacher bench but uses the other side as so you are curling with a 90 degree angle. -Wiki-
