Full Sit-Ups vs Crunches

Full sit-ups are used by both the United States military and the American public school system to measure muscular endurance in the abdominals. However, a closer look at the exercise and you’ll see that you may want to incorporate other core exercises if you’re primary focus is to isolate and build definition in your abdominals.

Full Sit-Up Technique

In the traditional sit-up, an individual lies on their back on a mat with their knees bent and feet flat on the floor. They can place their hands behind their head or across their chest, and they bend forward at the waist, bringing their entire torso up off the floor until they’re sitting straight up. The major muscle in the abdominals, or the “six pack” muscle, is the anatomically called the rectus abdominis.

Rectus Abdominis Muscle

It originates at your pubic bone and then runs up the front of your torso and inserts at your sternum. When it contracts, it causes your spine to flex, or bend forward. During the beginning of the traditional sit-up, just as you curl up off the floor, your spine is flexing, meaning your abdominals are primarily handling the force production for that movement to occur.

As you near the midpoint on your way up, however, you stop performing spinal flexion and instead you start bending forward at the waist, performing hip flexion. During this time, your abdominals are isometrically contracting to prevent your spine from collapsing backwards, but it’s your hip flexors that assist in the second half of the pathway of movement and bring you to a full sitting position.

Proper Crunch Technique

A crunch is performed by getting in the same starting position as a sit-up, but you raise your head and shoulder blades just inches up off the floor before returning them to starting position. Therefore, crunches differ from traditional sit-ups in that they stop where the hip flexors come into play, which in turn means they more effectively isolate the abdominals.

Sit-Ups vs Crunches – Conclusion

In the battle of sit-ups vs crunches, does that mean that crunches are superior? That depends on your fitness goals. If you’re trying to develop that muscular tone of a “six-pack,” then you’re going to want to choose exercises that specifically and effectively isolate your rectus abdominus. Thus, you would do better with incorporating crunches into your workout. If you’re looking to improve your physical function, however, and be able to actually sit up from a lying down position with more ease, then a full sit-up would be a much more functional and effective exercise to complete.

Plus, it’s important to note that in a full sit-up, although your abdominals are being assisted by your hip flexors, your abdominals don’t ever get to take a time out. As noted previously, your rectus abdominis is still isometrically contracting throughout the entire movement in order to prevent your spine from collapsing backwards. Therefore, unlike during crunches, in a sit-up, your abdominals have to handle both concentric contractions during the first half of the movement, and isometric contractions during the second half. This more closely mimics the types of work that your abdominals have to handle in real life.

Note on Crunches

If you are working towards developing a “six pack,” you can further isolate your abdominals by tweaking your crunch technique. Even during a crunch, your hip flexors are assisting to a small degree. However, if you were to pick your feet up off the floor and rest them on a chair of exercise ball, you would place your hip flexors in an ineffective position and require your abdominals to do nearly all of the work.

About The Author

Kim Nunley - Article AuthorKim Nunley has worked in the health and fitness field for over 10 years. She received her Master’s of Science Degree in Kinesiology from California State University, Fullerton and is a Certified Strength and Conditioning Specialist (C.S.C.S.) through the National Strength and Conditioning Association. She has been a personal trainer, strength and conditioning coach, physical education instructor and athletic coach, and now works as a freelance writer. She also writes short and feature-length screenplays.

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