Powerful exercise for upper and lower abs.
Lie on the floor on your back with your legs straight and arms extended straight back behind your head.
As you exhale, slowly raise your arms and legs, as if you try to touch your feet with your your hands at the top. (but position your hands parallel to legs).
As you inhale return to the starting position.
Do this exercise slowly to prevent injuries in your lower back.
If the exercise is too dificult for you, you can bend your knees instead of keeping them straight.