The video that I filmed today is a leg raise. Leg raises are done like the picture below and are an effective workout for your lower rectus abdominals. Leg raises can be done using a leg raise machine, but we can still do it just by lying down on the ground. In fact, if your deltoids are weaker than your abs, your deltoids and triceps might get worn out before your abs get stimulated, so if that is the case for you, you might want to do leg raises lying down first until your deltoid muscles get stronger.
Below is the video like. Enjoy!
Video Link: https://www.youtube.com/watch?v=G775jECBESM&t=2s