Researchers used electronic sensors to track the muscle contractions of 16 volunteers while they performed traditional crunches, as well as other abdominal exercises using popular equipment like the Ab Roller, Ab Wheel, and Ab Coaster. Compared to the machines, the crunches were far more effective at working abdominal muscles.  But before you lose the equipment and commit yourself solely to sit-ups, know this: Crunches alone won’t give you a fully toned core. “There’s no single exercise that challenges all of the muscles in the abdominal region,” says Cedric Bryant, ACE’s chief science officer. All the crunches in the world won’t target your obliques, the muscles that run along the sides of your torso and help you rotate and bend, and they also won’t work your transverse abdominis, which stabilizes your lower back and helps pull your belly in.  Your best bet? “Do crunches in combination with various types of planks,” Bryant says. “A front plank and a side plank would compliment the crunch or curl type of exercise.” More from Prevention: Have You Signed Up For Our 28-Day Challenge Yet?