Biowolf:
Side bends with dumbbells are classic exercise.
Here is the picture which shows how it is done
http://www.hardcorebodybuilding.com/sidebend.htm
If my lower back hurts, I would not do side bends with dumbbells either.
The waist twists I have described is what I do and I do not know anybody else who does.
Here are some alternatives.
(1) I have seen very good oblique machines which allow to add resistance to the waist twist movement, but my gym does not have one like that.
(2) People use barbell bars on their shoulders to do twists, the problem with it is that the only resistance you get out of it is because of the inertia of the bar and people end up doing jerky fast movements to get more resistance, this is not good and I find it not very effective.
(3) There are what is called Russian twists in which you lay on the floor and keep a plate (barbell plate) in front of you and twist the torso. You have to lift the torso a bit and this is not good if the lower back hurts.
What I do is simply what I have described, I use cables to get resistance in my waist twists, I make sure that the lower body is locked by kneeling all the way (so my butt touches my feet), i extend my arms fully in front of my torso and I grab the cable and rotate my torso using obliques pulling the cable. I will attach a drawing to this post which will show it.
This exercise works for me.
<IMAGE HOSTING WEB SITE IS DOWN, I WILL ATTACH PICTURE WHEN IS UP, OR WHEN I FIND A DIFFERENT ONE>
I hope this is clear, if something is not let me know.
As you know, I am not a pro trainer or anything like that.
jclayton: lets have mkgil better explain why. The fact is that I can find many links which say the opposite, that the abs area is mostly fast twitch fibers and that one need to go heavy and short sets.
I do long sets for abs, except for obliques, I believe more weight and more overload is better for the joints which will adapt to it and thus better for my spine.
Long endurance sets are great, but I find them not that great for my joints, short heavy sets (3-reps to 30 reps) with recovery time provide the best way for body adaptation to increase levels of stress/weight and their health.
Robert