The glute-ham developer (GHD) sit up is an oft misunderstood exercise. It is actually an explosive movement and should not be done slowly. Watch this video to see the difference between a badly executed GHD sit up and one done properly.
Point of instruction:
- Sitting in the proper place on the seat pads
- Proper positioning of the neck
- Bigger range of motion
- Explosive movement and involving the legs on the way up