Your “abs” are actually one muscle called the rectus abdominus. It’s a sheath that runs from your chest bone to your pelvis. The reason a six-pack looks like six separate muscles is because tendons run horizontally across the sheath, cutting ravines into the muscle.
The muscle tapers as it runs downward: It’s much wider up top near your ribs than it is down by your hips. You just don’t have much muscle to work with in your lower abs.
But with a very precise exercise, you can target the lower part of your rectus abdominus to make it grow, according to a column Schoenfeld wrote in the May 2016 issue of Muscular Development magazine.
The best exercises for muscle growth are ones that cause a muscle to shorten and lengthen, Schoenfeld says. Isometric exercises like planks do build strength and size, but they keep the muscle contraction static. There’s something about a dynamic contraction that has a bigger impact on muscle growth, he says.
So how do you make the lower part of your six-pack muscle shorten and lengthen? You have to tilt your pelvis in toward your belly button, Schoenfeld says.
You can do that with a reverse crunch - but not the way most people perform the exercise.
Instead of lifting and lowering your legs, focus on tucking your pelvis in toward your belly button and back to neutral.
That forces the lower portion of your rectus abdominus to shorten and lengthen while lifting the weight of your lower body. Check out Men’s Health Fitness Director B.J. Gaddour perform the exercise in the video above.
Try it - you’ll notice way more of a burn in your lower abs than you do with the traditional reverse crunch.
DO THIS: Lie face up on the floor or a bench. Bend your hips and knees 90 degrees. Tilt your pelvis forward toward your belly button. Return your pelvis to a neutral position. That’s 1 rep.
To challenge your lower abs even more, try a hanging knee raise that focuses on tilting your pelvis.
DO THIS: Grab a pullup bar with a shoulder-width, overhand grip and hang from the bar with your knees slightly bent and feet together. Tilt your pelvis in toward your belly button. Return your pelvis to a neutral position. That’s 1 rep.
This article originally appeared on Men's Health