A crunch is kind of a beginner's sit-up. In the crunch the exerciser lays on their back on the floor and bends their knees to place their feet bottoms flat on the floor - just like when preparing for a sit-up. And the arms are either crossed over the chest or bent so the fingers rest lightly against the back of the head, and once again you do not lift with the hands, you ONLY lift using the abdominal muscles, however, it differs from the sit-up in how far you lift.

For a crunch you only lift your shoulders from the floor, hold, and return to the start position. Do not lift toward the knees as you would in a sit-up, just lift shoulders from the floor and return to the start.

This same basic position and abdominal focus makes the crunch a great way to start strengthening the abdominal muscles for learning to do a sit-up.