Roll-Up (Be careful! Go slowly with awareness)
This exercise is great for strengthening the abs, but dangerous for weak backs. Be careful,don't overdo it, or maybe just skip it.
Lie on your back with your knees up. Anchor your lower back to the floor. As you inhale, raise your arms over your head, by your ears. As you exhale, slowly arc your arms toward your legs and begin to lift your head and shoulders off the mat. Always maintain awareness of your lower back: keep it pressed against the mat. Inhale as you roll down. For beginners, that is all.
Harder: As you come up, grab your thighs and pull yourself up a little higher. If that is easy, try this: Without grabbing, as you bring your arms forward, slowly roll yourself all the way to sitting. That is a roll-up. Don not use momentum to throw yourself forward; curl up with slow control. Keep your tummy tucked in (scooped).
Harder: do it with your arms crossed over your chest. Harder: Fingertips behind your ears, elbows back. Try it with your legs straight or soles of the feet together.
Start with five repetitions. Stop if your back hurts at all. Keep breathing. Enjoy.