“The L-sit is performed by supporting the body entirely by the arms and holding the legs straight out in front. The legs’ posture in the L-sit places an enormous, if not unbearable, moment or torque about the hip that must be counteracted by the abdominals to keep both the legs up and the spine from hyperextending. The exercise is isometric; i.e., it involves no joint movement. Being isometric, we quantify its performance not in reps but by time. As for efficacy, the L-sit may have no peer among abdominal exercises. We make this claim not on the basis of our position on abdominal muscle functionality but on the simple observation that athletes who have developed their L-sit to the point where they can hold it for three minutes subsequently find all other ab work easy. The gymnasts’ unrivaled capacity at hip and trunk flexion is in large part due to their constant training and practice of this exercise.”
—Greg Glassman, from “3 Important Ab Exercises,” May 2003.