The machine crunch is a machine-based exercise targeting the abdominal muscles. It involves sitting upright in the machine and curling the torso down against a pre-set level of resistance. On some machines, the knees also curl up toward the torso. Crunch machines usually use extra resistance in the form of selectorized weight stacks or plate loading, and are often performed for moderate to high reps, such as 8-12 reps per set or more, as part of the ab-focused portion of a workout.
Works the rectus abdominis or "six-pack" muscles
Allows for progressive overload in ab training
Machine makes it difficult to cheat form
Weighted ab training can help the core muscles grow and look more defined