Preacher Curl with Dumbbells When performed correctly, this exercise has the same action as the concentration curl. The concentration curl is the primary distinction between the two lifts. While the preacher coils on the pad, your upper arm rests on the inside of your leg. You cannot use your body to assist with the lift in either exercise. Instead, focus on pulling the weight through your forearm until it reaches your bicep. The preacher curl is used primarily for its appearance in a bodybuilder's chest. Since your upper arm is resting on your thigh, more muscle can be used to create a bigger look. This is not usually recommended during regular training because it limits the amount of weight you can use. Concentration curls are done using only one arm at a time. With this type of lift, all the muscles involved in the movement help to control the weight being lifted. Your body provides resistance, so less muscle means less strength. This is why most people only have enough concentration to lift 1-2 pounds. Preaching allows for more muscle usage and thus looks better (although this is also limited by weight). It is believed by some that preaching helps to strengthen the shoulder joint. Although this is true, it is not the main purpose of the exercise. There are two types of curls that involve only one arm at a time: concentric and eccentric.