[b said:
Quote[/b] ([xeno]Julios @ June 07 2003,2:40)]is it important to keep your back completely straight, and maintain the arch?
Julios,
Actually, you want just the opposite. Here is a pic of rectus abdominis, the muscle responsible for Cal's nice 8-pack.
Rectus Abdominis
Please note that the muscle is attached to the lower part of the pelvic girdle and the bottom of the rib cage. It's "job" is to flex the lumbar spine. Your lower back should be bending and unbending with each repetition.
Many people work their abs isometrically with leg lifts and sit ups with very little motion in their lower back. However, to work this muscle properly, you need to treat it like any other muscle... you bring the two attachments together in a controlled motion against resistance while forcing said muscle to perform the job it was "designed" to perform.
Try this to get a feel for what I am saying: Lie on your back on the floor with your knees bent.
Slowly press your back into the floor and picture your spine curling up one segment at a time as you squeeze your hips and ribs together.
Don't throw yourself up and don't be in a hurry to get there... using momentum takes the resistance
off the targeted muscle. I like to tell my clients to picture a rolly-poly or pillbug if you've seen one of those... As you slowly lower yourself back to your starting postion, try to feel the abs resisting. At the bottom of the motion you should be able to slide a hand between your lower back and the floor.
Doing this motion on the floor is fairly simple once you get a feel for it. It's a lot tougher to keep this motion going while on a machine, because it's a lot easier to allow the "wrong" muscle to do the job for you.
I'd recommend you do some good old fashioned crunches on the floor as a warm up to train proper motion in the abs (in the massage biz we call this neuromuscular reeducation) and then try to reproduce it while doing weighted work.
Once you 've got the form and progression figured out, do remember this. The two best exercises to perform to really bring those abs out? Putting down the fork and moving away from the table.

Past a certain point it really
is about diet.
Kate