Optimal sets and reps: 3 to 4 sets of 15 to 30 reps As you come up in the traditional sit-up, twist your torso toward one side, bringing the opposite elbow toward the knee on the twisting side.

The main difference between sit-ups and crunches is the range of motion involved in each exercise. Sit-ups require you to lift all the way up, while crunches require a slight lift off the ground.