I do these ab training sometimes to feel burn on my abs but these abs training can be too hard for somebody who has never done it. Always use a discretion and don’t do it if you feel in pain.
Stretch before or after?
Generally speaking, static stretching should be done after strength training. But if the stretch is related to certain movements for the sport such as gymnastics, it may be beneficial to stretch before the exercises.
It is so tough to do it on the floor. I started with using kettlebells. Keep your legs straight out and hold the position. You will feel “burn” on your abs right away. In order to progress, you can start with hanging crunch position and just hold. Get one leg straight alternatively to make this exercise slightly easier.
Pretty much the same as L-sit but this one you need to spread your legs. You will feel tensor fasciae latae working. I found it is very tough on that muscle and you need to get used to it over time.
Both L-sits require certain flexibility, especially straddle l-sit. You need to stretch your hamstrings often to be able to straddle l-sit.