GHD Sit ups:
I've used them off and on for over, I'd say, 20 years.
This issue is entirely with how they are performed. You see:
1. Too fast.
2. Too sloppy
3. Too much volume
4. Used for "met-con" purposes. Which relates directly to points 1 and 2. Using GHDs to elicit a rapid heart rate and large energy use is just stupid.
For me, 2-3 slower sets with me reaching down and touching the floor, for 10-12 reps was plenty of work. If you have to blast them with high reps, then it's not being programmed right.
Due to the positions, which can be precarious, it's got a big potential to hurt something. The suggestions Glassman wrote to help mitigate those are silly and useless.