The Abmat

The Abmat is an excellent training tool. It's purpose is to put or back int he correct position and ensure full range of motion during a regular sit up. I don't feel like giving it all the hype like they do on television and say that you'll get a six pack from using it, so I won't. What I will say is that this WILL help develop abdominal power and co-ordination at a low cost. (or free I will mention at the end)
as with the GHD sit up we have learned that we don't need to bring our sternum closer to our pelvic bone to create great "core strength" or mid line stabilization. There is a powerful set of movements you can do by keeping your back in a flexed position during the situp.
Opening your hips into a butterfly position will be even more powerful.
All of these movements will enforce a FULL ROM which is often cheated without even knowing it during a regular sit-up. I have personally felt the power of these helping to alleviate daily back pain, in combination with some other movements.
By cushioning the lumbar, the Abmat forces you to rely solely on abdominal effort to move your torso through the full range of motion. The opportunity to engage your hip flexors for that initial “umph” at the beginning of the movement is gone. Instead, your lower abs alone are left to do ALL of the work.

If something is injured it will require rest time, but at some time you will need to SLOWLY and gradually strengthen it again, so that you can avoid re-injury.

for more information here is an article from backbuilder.com click here
this article is a great break down of the mechanics during both traditional and abmat situps.

Free abmat:
The thickness is aprox 2 inches at the max height. I found folding and rolling a towel to be semi effective. With time and numerous reps you will have to re-adjust the folding and rolling, But a great substitute for no money. My towel has pushed me to purchase these for the gym... I suspect people will be asking me for them after a couple weeks.