Twisting Crunch

The twisting crunch adds rotation to trunk flexion, which is the combination that actually reaches the obliques. A straight crunch trains the rectus abdominis almost alone; turning the torso as you rise brings in the internal and external obliques, the muscles responsible for rotating and stabilising the trunk in nearly every athletic movement. Reaching the arm across toward the opposite knee gives the rotation a target and keeps the range consistent from one repetition to the next. Speed is what usually ruins it. Performed quickly, momentum carries the torso across and the obliques barely contract, so move deliberately and pause briefly at the point of maximum rotation. Keep the arms extended and the chin off the chest rather than leading with the head. Reaching with the arm rather than the shoulder is the other common error: the hand should follow the torso across, not lead it, or the rotation happens in the shoulder joint and never reaches the trunk at all.