What is diagonal curl-up (arms extended)?

Diagonal curl-up (arms extended)

1. Lie on your back with your knees bent and your feet flat on the floor. Your arms can rest at your sides.
2. Slowly tighten your belly muscles and raise your head and shoulder blades off the floor. At the same time, reach to one side with both arms. Keep breathing normally and don't hold your breath.
3. Keep your neck straight and don't press your chin to your chest.
4. Hold for 1 to 2 seconds. Then slowly lower yourself back to the floor.
5. Repeat 8 to 12 times.
6. Repeat these steps, reaching to your other side.