Build Core Strength and Endurance with Chair L-Sit The L-Sit on Chair is a challenging exercise that targets your core muscles, including your rectus abdominis, obliques, and transversus abdominis. It also strengthens your hip flexors and quadriceps. This exercise is a great way to improve your core strength, stability, and endurance. In this video, we will show you how to do the L-Sit on Chair safely and effectively. We will also discuss the benefits of this exercise and provide tips for gettin