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What Do Crunches Do for Your Body?

author image Brian Connolly
Based in the Appalachian Mountains, Brian Connolly is a certified nutritionist and has been writing professionally since 2000. He is a licensed yoga and martial arts instructor whose work regularly appears in “Metabolism,” “Verve” and publications throughout the East Coast. Connolly holds advanced degrees from the University of North Carolina, Asheville and the University of Virginia.
What Do Crunches Do for Your Body?
The abdominal crunch is a popular exercise for strengthening core muscles. Photo Credit: Wavebreakmedia Ltd/Wavebreak Media/Getty Images

The abdominal crunch is among the most common exercises for toning the core muscles. Typically performed while lying face-up on the floor with your knees bent, abdominal crunches tone and strengthen the rectus abdominus and surrounding core muscles, improving your posture and allowing you to lift and rotate your body more effectively.

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Abdominal crunches are a classic core exercise for defining the abdominal muscles. However, contrary to popular belief, crunches do not actually burn stomach fat. Instead, by toning the rectus abdominus and oblique muscles, your core muscles gradually tighten into the shape of the popular six pack. To create a sculpted appearance, however, you must combine your core muscle workouts with aerobic exercise to remove the fat covering your muscles.

The Physics of Crunches

As you lift your chest towards your knees, the rectus abdominus muscles contract and tighten, supporting the elevation of your upper body. The workout to your core muscles gradually increases as your body approaches a 45-degree angle to the ground, potentially causing your abdominal muscles to shake. By adopting a regular crunches regimen, your muscles strength and increase in mass and density, allowing you to perform more crunches each set.


A study performed by the American Council on Exercise compared various approaches to the abdominal crunch and determined 13 exercises that are cause high levels of activity in the rectus abdominus and oblique muscles. The vertical leg crunch, a combination of the abdominal crunch and the leg lift, was ranked in the top-five for both muscle groups, while the reverse crunch ranked in the top seven. If you find your regular abdominal crunch exercise is becoming less and less effective, boost your core muscle workout by performing a high-ranking abdominal crunch variation.

Safety Concerns

Like all exercises, the abdominal crunch carries the possibility for injury. Refrain from neck and spinal strain by crossing your arms over your chest instead of gripping behind your head. Also, tighten your abdominal muscles as you lift your upper torso off the ground to reduce the impact on your spine. Talk to your doctor if you are new to core exercises or are unsure how your body will react.

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