What Muscles Do Sit-ups Work?

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Sit-ups work your core muscles but you may wonder which ones. Additionally, this exercise will work some of the muscles involved more than others.

First of all, a sit-up with good technique involves curling up your chest and bending your spine. This is important when it comes to what muscles you use.

With this technique, sit-ups mainly work your ab muscles but also your hip flexors in good amounts and oblique to some extent.

Especially the upper and middle parts (but also the lower part) of your ab muscles will have to work during sit-ups.

Keep in mind that if you want to see your bigger core muscles, your body fat percentage has to be low enough.

Sit-ups are not good for weight loss so to achieve this you will have to consider other exercises and lifestyle changes.

That aside, in theory, you can also do sit-ups in a way where you keep your spine straight. In this way, you would mostly engage your hip flexor muscles.

Muscles Worked With Sit-ups

Sit-ups muscles worked

If you look at how to do sit-ups, you see that this movement involves curling up your shoulders and then moving your upper body to your knees.

This mainly works your ab muscles and hip flexors but also your oblique muscles to some extent.

Ab muscles also known as the rectus abdominis

The ab muscles, also known as the rectus abdominis, are the muscles that run along the front of your body. If people say six-pack, they mean the ab muscles.

These muscles are responsible for bringing your chest toward your hips (and the opposite).

Compared to their relative strength, the ab muscles will typically have to work the hardest in the sit-up exercise.

Sit-ups target all areas of the abs to some extent but especially the upper muscle fibers. After that, the middle part will have to work a good amount.

Lastly, sit-ups do work the lower abs to some extent but not as much as alternatives like reverse crunches.

Hip flexors

Next, sit-ups also work the hip flexors which include the psoas, pectineus, iliacus, rectus femoris, and sartorius muscles.

In simpler words, these are the muscles that run between your thighs and your hips in the front of your body.

The hip flexor muscles are responsible for moving your thigh toward your hips and back.

In sit-ups, these muscles will have to work in the last part of the movement to lift your lower back off the ground so that your chest can move closer to your knees.

If you do sit-ups in a way where you keep your spine straight, you would mostly engage the hip flexors.

Oblique muscles

The obliques or external and internal obliques run along the side/front of your upper body.

These muscles are responsible for tilting your upper body sideways and rotating it.

The oblique muscles do not have to work that hard in sit-ups.

That being said, they do engage them to some extent to keep your upper body at the right angles.

Can you get bigger abs, hip flexors, and obliques from sit-ups?

Something important to keep in mind is that just doing resistance training exercises like sit-ups a few times is often not enough to see significant results.

You need to implement the right resistance, repetitions, sets, and rest time too.

How much weight, how many sit-ups, and how much rest this comes down to depends on details like your body and training goals. However, there are some general guidelines to get you started.

To build bigger abs, obliques, and hip flexors, you want to do around 3 to 6 sets of 6 to 25 sit-ups with a resistance where you are just able to complete these ranges.

Even if you don’t have the equipment to do sit-ups with weights, sets with up to 50 repetitions and potentially even more reps can work your muscles enough for growth too.

You do really want to push to muscle failure in these higher-repetition sets.

As you get stronger, you will have to increase the weight, repetitions, and/or sets in your sit-up routine to keep growing and strengthening your muscles.

Should you do sit-ups every day?

After working bigger muscles like for example your glutes, it is typically recommended to implement a rest day in between workouts. This is to make sure your muscles have enough time to repair and grow.

You can do this when growing your abs, obliques, and hip flexors with sit-ups too. However, because these are smaller muscles many people can do a routine like 100 sit-ups a day without m(any) issues.

Actual muscle growth aside, keep in mind that you may have to lose more body fat before you can see these bigger core muscles.

Muscles worked sit-ups vs crunches

There are a variety of core exercises but many people like to compare sit-ups and crunches because they are basically the most popular ones.

If you don’t know crunches, these are an exercise where you start similar to sit-ups but you raise your shoulders as much off the ground as possible while keeping your lower back on the ground.

This makes it so crunches mainly work the ab muscles. Especially the muscle fibers in the upper part.

On the other side, sit-ups also work the upper abs but focus just a bit more on the middle abs too.

Additionally, this movement works your hip flexors and obliques more.

In terms of muscles worked, sit-ups are not necessarily always better than crunches. Depending on your training goals, preferences, and capacities, you can choose one or the other.

Do sit-ups work lower abs?

Sit-ups do work your lower abs a good amount but the focus will be more on the upper and middle parts.

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Matt Claes founded Weight Loss Made Practical to help people get in shape and stay there after losing 37 pounds and learning the best of the best about weight loss, health, and longevity for over 4 years. Over these years he has become an expert in nutrition, exercise, and other physical health aspects.