I'm looking for some serious advice on how to do sit-ups. Even as a kid, I was never able to do them. Training advice is to do 10-15, break, another 10-15, break and so on. The trouble is, I struggle to get 8, after which I strain but don't move at all, even after resting. It seems that no amount of repetition increases this number. Been trying about 5 times per week for the last 4 weeks and still no better. I managed to get 20 during the PFT, but 12 of these were achieved by rebounding off the rubber mat. It's been suggested to me that I try strengthening my stomach muscles by doing leg lifts. This is no problem to me - any number, any duration, any speed - so I don't really think that the muscles are the problem. I'm wondering if it's a function of spine shape. When I lie on my back, I can easily get my hand underneath the small of my back - In fact, I can get most of my forearm under. And I can't force my spine onto the floor, the gap remains, no matter what. Also, trying sit-ups without a firm anchor on my feet just results in leg-lifts. Am I inadvertantly locking my spine into the opposite direction to that needed to do sit-ups? Any advice will be gratefully received, especially as I can't find any posts that suggest that other people have trouble with sit-ups.