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Will My Abs Know the Difference Between Crunches and Sit-Ups?

My brain certainly doesn’t

I’d lived with sit-ups as the only tool in my arsenal for training my midsection until my first day of organized weight training for the high school swim team. It was at that point that I was introduced to the crunch as a replacement movement. As Coach Harding demonstrated his expectations for what constituted an acceptable crunch, and then explained that we should perform as many as we could in the 30 seconds he was allotting us before we switched movements, my teenage brain interpreted his instructions as an invitation to sloppily sprint my way through as many reps as I possibly could until he blew the whistle to signal the switch. 

At some point in my brief high school athletic career, I decided that crunches were just lazy sit-ups, and while everyone else on the team may have been content to do regular crunches, I had to take it upon myself — as a self-appointed leader and example-setter for the team — to do full sit-ups as a way of showcasing that I demanded better of myself, and therefore they should have done so as well. After all, sit-ups involved far more movement than crunches, and to my way of thinking, that automatically made them more difficult, and therefore a better showcase for my brawn. 

So here’s the question: Was I right? Are sit-ups better than crunches? Does all of that extra movement equate to sit-ups being a better overall exercise? Or was I an unwitting victim of my own desperate desire to look like a hero?

That’s a lot of questions! First of all, what’s the difference between a crunch and a sit-up?

Knowing the differences in form and function between crunches and sit-ups is very beneficial to you as you walk the precarious path to fitness knowledge, because you can apply it to several other muscles, and you’ll understand why some exercises are more optimal than others depending on what you’re training for.

Crunches emerged by that name in the late 1970s and early 1980s as an exercise that was alternatingly described as “advanced” or “basic” depending upon who was offering the description. Until it gained widespread recognition, the crunch was often appended in such a way that it was referred to as a “sit-up crunch,” a “crunch sit-up,” or even a “quarter sit-up” or a “half sit-up.” It was well into the 1990s before crunches were sufficiently recognizable as a movement all their own and were able to fully distinguish themselves from sit-ups.

The basic movement of a crunch involves keeping your lower back on the floor, and contracting your abdominal muscles in such a way that it causes you to bend just below your sternum as you push your chin, shoulders, chest and everything above the midline skyward. When you release the contraction, your shoulder blades slowly return to the floor. Done properly, the crunch will allow you to repeatedly contract the muscles of your abdominals, pumping blood into them, and shaping them in a way that will leave them looking well-defined and shapely, but not particularly large. 

Ideally, the initial motion of the sit-up would mirror the entire crunch movement. However, the sit-up goes an additional step of recruiting your hip flexors to pull your upper body completely off the ground. Depending on the position you’re in and how your feet are anchored, you may even find yourself leaning forward to such an extent that your abdominals cease to contract. 

Regardless, sit-ups can be clumsily defined as crunches with additional recruitment from the hip flexors, which may be of beneficial assistance if you’re hoping to use a sit-up as a literal training tool to condition yourself to move from a supine position to a seated position before you rise and lift yourself up from the ground.

So which exercise should I do?

I hate to say this, because I absolutely adore sit-ups, but there are compelling, logical arguments to be made that no one should ever do sit-ups under any circumstances. Straight out of the gate, sit-ups promote excessive curvature of the spine, so executing them runs the risk of damaging discs in your back. 

Every time you perform a sit-up, you overload your spine with unforgiving compressive forces that can ultimately lead to serious spinal damage. Also, there are far safer ways to train your hip flexors in general, including several different leg exercises. There are even ways to train your hip flexors in conjunction with your abdominals that are far safer, including leg raises, and hanging leg raises. Again, I wish this wasn’t the case, but sit-ups are virtually impossible to execute safely.

The good news is, sit-ups aren’t an essential training movement. Crunches are simpler, safer and arguably more effective when it comes to building the sort of abs you’re looking for. So even if crunches did ironically start off being defined as 25 percent of a sit-up, they’ve proven themselves to be 100 percent superior for the long-term health of your back.