Curl-up vs. Sit-up: which one is better?

Curl-up vs. Sit-up: which one is better?

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Thousands of people do sit-ups by the hundred, hoping to get six-packs. This article will show you which muscles you actually use for sit-ups and it will also reveal whether curl-ups or sit-ups are better for building your abs


Curl-up or sit-up - the eternal battle

Sit-ups are the first thing on most people’s minds when they hear the expression “abdominal exercise”. This is kinda burned in our subconscious and cannot be erased. Most of the people who start doing their abs will most likely start doing sit-ups. This is what they made us do in PE classes back then, and this is what the media keep pushing into our faces.Sit-up “to rule them all”. But if you have ever delved into the kinesiologic or anatomic aspects of workout, or you simply have the mind-muscle connection while doing an exercise, you might have noticed that there’s something fishy about this whole sit-up thing.

And you might be right. 

Always focus on the muscles you are targeting.

Easier said than done, I know, especially because sit-ups will bomb your abs, too. I never said they wouldn’t. But it’s worth examining which muscles are doing most of the work during the different phases of a traditional sit-up. 

When do your abs contract? When you are crunching your rib cage towards your pelvis by curling up your spine. So, lay on your back now to test how far you can curl up your spine. In other words: how far can you “sit up” by curling your spine ONLY. Remember: you should only go to a point where you can still curl your spine up, but no further!

I’m telling you: the most you can lift up from the ground will be your shoulder blades. And this is the point where you couldn’t go any further without actually snapping your spine in two (fortunately, this is not much likely to happen :)). Hold this position for 10 seconds and you will feel that your abs could not be contracted any further.

So, where are we now? Your shoulder blades are lifted up from the ground; your abs have reached the peak-contracted position; and you still haven’t sat up! It’s starting to get fishy, isn’t it?

Now start to sit up slowly from this position. (You’d better anchor your feet somewhere.) And look now: where are you feeling muscle contraction? Alright, your abs are contracted as they should, to keep your trunk stable, as this is very important in order to avoid overloading the sacral vertebrae. 

So, which muscles are contracted now? Strange as it may seem, but you will feel “some muscles” working in your thighs and at your hips. And you are right: these are the hip flexors. After your abs have reached their peak-contracted position, you will perform the upper phase of the sit-up using these hip flexor muscles. In the below pictures you can see exactly which muscles are involved in this job. You see any abs?

Curl-up vs. sit-up: sit-ups work auxiliary muscles, too Sit-ups work the thigh muscles, too Hip flexors are also helping while doing sit-ups

No. Instead, you can see the Rectus femoris, theSartorius, the Tensor Fascia Lata, Psoas major and minor and the Iliacus. These muscles have little to do with six-packs. Are you sure you want to work them?

But what’s wrong with that? My abs are still working, aren’t they?

Sure, they are. And a bunch of other muscles as well. Plus, as a consequence of the nature and the load angles of the sit-up exercise, the lumbar vertebrae will be exposed to a considerable amount of stress. Moreover, if your abs are already worn-out but your hip flexors are still holding on, you will most likely overload your sacral vertebrae, too, if you go on doing more sit-ups. This happens when your abs can no longer stabilize your trunk, but the hip flexors can still lift your spine. 

Anyway, it is unnecessary to perform an exercise in which the targeted muscles are only working through half of the range of motion, while the other half is probably useless for you.

Here is the best related video you can find online.

Does that mean I shouldn’t do sit-ups at all?

Well, if your goal is to develop spectacular abdominals (“six-pack”), curl-ups are definitely more useful for you. But if you intend to improve the stabilizing function of your abdominals and hip flexors, you should do sit-ups. But remember to perform this exercise in a slow and controlled manner; your back should never be bent over 180 degrees backwards and you should hold the core muscles of your trunk tight all along to reduce the stress on your spine to the minimum. 

But if your goal is a six-pack, go for curl-ups and don’t waste your time on sit-ups.


(To avoid confusion: ab workout will build your abs but nothing more. Workout in itself may only make your abs look “nice” under the (thicker or thinner) layer of fat covering them; but it won’t reduce the amount of fat. To get a real six-pack, you have to diet – editor’s note).

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