The L-sit Chin-up is a killer exercise with a movement that is borrowed from gymnastics. It helps strengthen the abdominal muscles, hip flexors, shoulders, back, biceps, and builds up your entire “core”. Your core strength involves all of the muscles of your abdominal region and back, and they are critical for supporting your spine and keeping your body stable and balanced during many different exercises and weightlifting movements. The stronger your core is, the better you will become at lifting weights and body weight exercises; plus you will reduce your risk of injury.
In order to be able to perform an L-sit Chin-up, you do need to be comfortable doing chin-ups and have enough abdominal and core strength to hold your legs straight out in front of you. You can work up to this by, obviously, doing a lot of chin-ups and pull-ups to build up your arm and shoulder strength. To build up your hip flexors and abs for this movement, work on knees-to-elbows (see video here) and toes-to-bar (learn more) ab exercises while hanging from a pull-up bar.