Lying Dumbbell Curl

The lying dumbbell curl is performed flat on a bench with the arms hanging at the hips, which places the upper arm slightly behind the line of the torso. That position puts the long head of the biceps on stretch before the repetition begins, and a muscle trained from a lengthened position responds in a way that partial ranges do not reproduce. Rotating the wrists from a neutral start to a supinated finish adds the second function of the biceps, turning the forearm palm-up, so the contraction at the top is stronger than in a curl that only bends the elbow. Because the bench fixes the back and shoulders, there is no momentum available and the weights will be lighter than on a standing curl. That is the point rather than a drawback. Time the rotation so it finishes as the dumbbells reach the top rather than starting it at the bottom, and let the arms hang fully at the end of each repetition.