effective ab core exercise

those are pretty much advanced i can't even lift my butt a centimeter off the floor!

Haha. I've always been able to do the L-sit ever since I was young, without even training towards it, just a natural I guess. The other things I had to work hard towards though, probably about 3 months to handstand really well and etc. Before doing those advance things I used one of those inflatable exercise balls, those are great for your core. Just do some crunches on them, do some roll ins, do some side-planks, and leg raises. A great one is when you hold a pushup plank, but you support yourself on your forearms, then move your hips side to side. That last one is pretty much all you need to do, it is unbelievable how much it works. I used to only do it for about 3.5 minutes, and I would have sweat dripping down my arms and face by the end, and I rarely work up a sweat with any other exercises. I am kind of a fitness nut ;).

i tried plank and i find it really great, but i was only able to hold my position for like 5 seconds? i am really not into building muscles but i want it toned, and because of the nature of my work (medical editor), sitting in front of the computer 8 hours a day 6 days a week, i really have no exercise at all.

situps are the most popular but it gives me backache after a few reps.