Originally posted by Griffith
Don't work them every day -- abs are like any other muscle and need rest.
They're not like any other muscle. They have much less potential to grow and recover much quicker.
You're safe working the abs every day as long as they're not sore. I hear about people injuring their arms, chest, legs, and shoulders from over-training all the time (and it's happened to me also, before I knew what I was doing). I don't think I've ever heard of someone hurting their abs. I certainly never have and I work them 5 times a week (would every day if I had time).
Also, I don't feel any burn when doing regular crunches. I'm pretty sure I'm performing them properly, but it seems like I can do them forever and not feel like I'm accomplishing much.
But if I do "bicycle" crunches, I tire out and feel the burn.
Do what works and mix it up so you don't get bored. I do bicycles, foot circles, flutter kicks, and scissor kicks (just like they sound - lie down with your hands under your butt and kick and move your feet). If you have a punching bag, wrap your legs tightly around it and jab/cross every time you do a sit-up. Go into pushup possition, but on your forearms instead - hold that possition for 1 minute. When this gets too easy, raise one foot. If you have a decline bench, do weighted crunches with that. Think of yourown.