Frequency and intensity of ab workouts?

Bunch of questions here...

- I have been doing abs 2-3 times a week. This is what the trainers at my gym say I should be doing. Supposedly I need to work my abs all the time. Is that necessary, or could I just hit them hard like any other muscle in my split routine with a "Abs and something else" day?

- As far as reps are concerned, everything I've heard is to keep my reps 15-20 on ab exercises. Why is this different than other muscles? Are abs more susceptible to injury if I increase the weight and lower the reps?

- The trainers say that if I lift too heavy with my abs I will 'lose definition and get a big block of abs'. Do the tendons that wrap over my abs tear/get covered up with muscle/get stretched out or something crazy --> causing a loss of 'definition'? Or is this just a bunch of BS from amateur college-student trainers?

- My goal with the rest of my routine is building muscle, and I want to do the same with my abs. A trainer told me that 'you can't really build your abs, just get them more defined'. I don't have a lot of body fat (~10%), and can see my abs sometimes. Shouldn't I be able to build my abs up to push out and be more defined?

from what i know you could train them twice a week, really hard/really heavy. I do cable pulldowns with my abs so that i can only do like 8 reps before my abs hurt like a bitch.

As for the block of abs... i've never heard that before in my life, and personally that sounds like a crock of shit.

I think your trainers are idiots. Your abs are just like any other muscle in your body. If you're looking to build size and strength, you're going to want to do 3x8 sets of weighted decline ab exercises. You can do it twice a week. For a trainer to say you 'can't build your abs, you can just get them more defined' ... you should demand that moron be fired immediately. Seriously, did he even go to more than a 1 hour company training session? That statement is so fucking stupid, I find it offensive.

How are you measuring your body fat? If you are at 10% ... you should see your abs clearly.

Rayns right, you can train your abs all year and still not have a six pack because its not visible on the top layer of fat. Work on the cardio more.

The gym I'm at has this little hand-held electrical-impedence thing to measure body fat (I think this is it (http://www.amazon.com/Omron-HBF-306C-Fat-Loss-Monitor/dp/B000FYZMYK/ref=pd_bbs_sr_1/103-0081145-1264679?ie=UTF8&s=hpc&qid=1186349384&sr=8-1)). I don't know how accurate it is, since it can only measure in the shortest path from one hand to the other, totally missing my stomach and lower body. It is consistent if i measure myself two days in a row. They don't have calipers.

I doubt the trainers really have much training at all. There is a pretty high turn over rate. Most of them are sales-types that spend their time trying to sell people tanning bed memberships and going to malls/public places aggressively recruiting new members.

All of the ab stuff i've been doing is just high volume. Is it possible that my abs aren't strong/big enough to be seen or is my bodyfat measure more likely off?

almost certainly your bodyfat

and those electrical impedence measurers are not accurate at all. Giving a consistent result only means it is consistently wrong.