Machine Crunches

Sit on the machine and adjust the seat so that the chest pad is at the level of your upper chest and, if available, buckle the seat belt (some machines will require you to cross your arms on the pad and others require you to lie in the machine hooking in your feet and arms).
 
Slowly curl your upper body towards your hips; return to the starting position.
 
The entire motion should be done in a smooth, controlled manner that lasts about 3 seconds, with the downward movement no faster than the upward.