Ya it's gonna sound corny, but I think that my long torso is the issue. See every time I've wanted to do situps, I've either had to kick or have my feet pinned to do it. Now this seems odd, since almost all the people I know can do situps from the regular position. Originally I reasoned that it was because I was out of shape, (and this might contribute to the difficulty anyway, but it should only disrupt the number of situps I can do.) But sitting there thinking about it, I realized that it was all one big lever problem. In a basic situp, the objective is to take and bend your body 90 degrees at the waist. I'm not sure about "normal" people, but this is an easy task. I can do that no problem. However, when I contract my abdominal muscles, my legs lift up and my torso only lifts slightly. Now why I would be different that a normal person in this regard makes since if normally legs are slightly more dense than torsos and heads (which I would expect to be true based on the density of muscle and the amount of muscle required to walk and jump and the like.) Couple that with an equally sized torso and legs and you get the counterlever needed to do a situp when dealing with normal people.
In my case however, I have about 8" of extra torso. This means that I also have 8" less leg to act as a counter balance. This means that the total effect is like having 16" of extra body tacked onto a normally proportioned person. Now, it's not exactly 16" worth of mass since it is actually 8" of leg density material and 8" of torso density material. But the ultimate effect should be obvious: my torso exhibits more gravity torque on the pivot point than my legs do. This means that when I attempt to do a situp, I apply the contracting force to try and bring together my legs and torso and my legs are the part that move, not my torso. So my feet come up and satisfy the basic objective of bending 90 degrees, but unfortunately don't exactly do what you'd expect from a situp.
This is, however, no excuse for my poor total situp count; well, it could be reasoned that by having extra torso, when I do a legs pinned situp, my torso exerts a larger gravity torque on the system than a normally proportioned person, but I feel that if I have more torso, then that's all the reason I need to be able to lift it. ^^ But it does explain why I need to pin my feet when I do situps and helps to ease my issues with not being able to do a normal situp.
Jim's Super-Ego: This is all just a rationalization and you know it!
Jim: I know that, but you don't have to remind me!
Jim's Super Ego: Quit rationalizing and goto bed. You have work in the morning!
Jim: Ya, ya, no need to get pushy.
Jim: I know that, but you don't have to remind me!
Jim's Super Ego: Quit rationalizing and goto bed. You have work in the morning!
Jim: Ya, ya, no need to get pushy.
Mood: Sleepy and Justified