Which Muscles Are Used in Sit-Up Exercise – Learn With Examples

The sit-up exercise is one of the most common bodyweight exercises aimed at strengthening the abdominal area. Is this information more than enough!

Sadly, many people stop at this stage itself and start doing sets after the sets of any exercise, including sit-ups.

Several muscles work in a team to build the motion we aim with sit-up exercises. 

Every exercise we perform involves primary and secondary muscles based on the role they play during the range of the motion of the exercise.


Here I am going to provide the details of muscles engaged in a sit-up. You will also gain knowledge about the sequence of their operation during the range of motion of sit-up.

I am sure; you would be mesmerized by the beauty of how the brain executes these movements. Don’t worry; I would keep this demonstration way too simple for grasping the idea in the first attempt.



So how muscles behave during sit-up exercise? Three kinds of muscles work during a classic sit-up exercise, namely – Rectus abdominis (abdominal muscles),  Illoposas (Hip flexors), and Rectus femur (front thigh muscles).  The abdominal muscles contract during the initial phase of sit-up exercise while the upper body is just lifting off the ground. The hip flexors and quadriceps start contracting in the final phases of the sit-up to move the upper back, even more, closer to the thighs.

Well, it is not that easy to understand the muscles this way. Several questions need to be answered, where they originate and end. What the hell hip flexors and quadriceps are doing in an abdominal exercise like a sit-up.


❝ Hi, I am Ravi, your companion and a passionate fitness athlete, cyclist, runner, gym enthusiast who just loves the concept of resistance bands for their extreme flexibility. I have been using resistance bands as one of my primary fitness equipment for the last many years ❞



Let us begin with the fantastic explanation –



The basic principle to be followed while examining sit-up exercise –

Here are the steps we need to take to explore the dynamics of sit-up exercise –

  1. Look for joints actively moving during the exercise
  2. Shortlist the joints, which are bearing the majority of the load.
  3. Analyze the muscles which are connected to that particular joint.
  4. Check for the behavior and role those muscles play while moving that main joint.

By the time we have completed the above steps, it is not hard to analyze the exercise for the kind of mistakes we are already doing and take corrective actions.



Joints actively participating in the sit-up exercise-

Before analyzing the movement of any exercise; Always come down to the active joints where all the noise is happening.

In case of sit-ups exercises, there are two joints which rotate actively during the sit-up exercise –

  • Hip joint
  • Shoulder joint

We turn our upper body around the hip joint, whereas the lower body is fixed in its position with feet landed firmly on the ground.  The shoulder joint moves to rotate the arms in line with the range of motion.

Quiet simple, Isn’t It!


Which joint is playing a majority of the role during the sit-up exercise!

The shoulder joint is only moving the arms through a small range. The movement is overall free, with only a load of arms.

The hip joint, in contrast, has to lift the complete upper body against gravity during the lifting/contraction phase of the sit-up exercise.

WINNER is the hip joint, which is taking the maximum pain and playing a lead role during the sit-up exercise.  

Now let us study the muscles which move the hip joint during sit-ups in the next section.


Know the muscles connected around hip joint (which plays some active roles in sit-up exercise)

Every joint in our body is connected to the muscles through the tendon. The tendon is an elastic and sticky white colored material that attaches every muscle to the skeleton.

There are three muscle groups connected around the hip area, which plays a vital role while executing the exercise.


A) Rectus Abdominis –

I won’t go into much depth as it won’t have much relevance for most of the readers in reference to sit-ups, at least. For curious people, there are kinds of abdominal muscles in our stomach area  – Rectus abdominis ( outer layer) and transverse abdominis (inner layer).

The rectus abdominis originates from the bottom of the rib cage and ends at the pelvis (hip bone).


? Amazing Fact


Every muscle we have in our body, only contracts ( reduction in length) from their original position when the brain sends it a signal to do so. Muscles never stretch from resting place. It is tendon (connecting muscles to the bone), which becomes stretchy with yoga and flexibility routines. 


B) Iliopsoas muscles –

The iliopsoas is the combined name given to the two muscles, which play a remarkably similar role. They behave like a twin baby, indeed.

Here are the two muscles which come under parent iliopsoas –


I) Iliacus muscles

These muscle originates from the hip bone and ends at the thigh bone whose scientific name is the femur.

When iliacus muscle contracts, they pull on the hip bone towards the thigh and vice versa. As a result, they are responsible for moving the upper body towards the upper legs or upper legs towards the trunk ( upper body).

In real life, when we wake up from the bed and lift our upper body to come in sitting position, these muscles play an active role.

They also assist in making the lateral movement of the upper body and thigh on the sides.


II) Psoas Muscles – 

These muscles work precisely similar to the iliacus muscles, with only difference in the origin. 

In contrast to the iliacus muscles, these muscles originate from the lower spine, which is technically named as the lumbar spine.

Just like, iliacus muscles, they are responsible for flexing (rotating) the hip joint for bringing thighs and upper body closer to each other. They are also accountable for twisting of the torso around the hip.

There are many more technicalities involved in the description I gave for these muscles.  However, the information provided here must be more than enough as far as the scope of this article is concerned.


C. Rectus Femoris

The rectus femoris is one of the four pieces of front thigh muscles which originates from the pelvis ( hip bone) and ends at the tibia (lower leg bone) through the patella (knee cap). 

Whereas the other three muscles originate from the femur (thigh bone) and end at the tibia ( lower leg bone).

As above, it is only rectus femoris, which is connected with the hip out of the group of quadricep muscles. That is the reason, rectus femoris is mentioned here while explaining the working of sit-up exercise. 


How the above muscles behave during sit-up exercise and who plays a final stroke –

This section of this article is the most crucial and equally much more enjoyable. Let us break down the sit-up exercise into the two parts to explain to you the role of the muscles I just described.

The sit-up exercise can be divided into two sections depending upon the kind of muscle groups that gets activated during the range of motion.

  1. The curl up section
  2. The hip lift section

Let us discuss each part of the sit-up exercise and look into the function of muscles behind the scene.


I) The curl up section-

This section of the sit-up exercise refers to the initial lifting/contraction phase of the exercise. It is the time when we are engaging the abdominal muscles (rectus abdominis) and contracting them to pull the rib cage towards the hip joint.


Here, the spine on the back starts curling up in the direction of the exercise. The main muscles which act predominantly during this phase are rectus abdominis muscles. 

All the loading work to lift the spine and the weight of the upper body parts are done through abdominis muscles.




During this section, there is no inward rotation/flexing of the hip joint at all except the curling up of the spine with the help of abdominal muscles.




II) The hip lift section-

The name given to this section does not mean that we are going to lift our hip to execute the rest of the portion of the sit-up exercise.

Here, we execute the final lifting left out after the rectus abdominis muscles have done their part to bring the back to a maximum possible height.

Now the only option left to the body to lift our upper body towards the thigh is to employ the hip flexors, i.e., iliopsoas muscles.

As we read in the earlier parts of this article, the iliopsoas muscles are connected from the lumbar spine and pelvis to the femur (thigh bone).

So, instead of further pulling the abdominal muscles from the rib cage towards the hip joint, the body employs the hip flexors to pull the upper body through the lower spine area.

It is also the time when the quadriceps muscles (rectus femur) also contracts to pull the hip towards the knees.



What are the significant risks associated with the curl-up and hip lift section of the sit-up?


During the hip lift section, our long spine/back has to take lots of pressure due to the force developed by the flexors acting on only the lower side of the back. Whereas, the bodyweight of the upper body parts tries to pull the chest, shoulders, and head towards the ground due to gravity.

The only way left to keep back safe and stable during this movement is to keep rectus abdominis muscles (abdominal muscles) contracted isometrically.


? What do we mean by isometric contraction?

The isometric movement of muscles refers to the activation of muscles without a change in length. That means the abdominal muscles are still playing an active role in stabilizing mode without further contraction.

So, to avoid the upper spine from bending towards the ground in contrast to the lower spine, the abdominal muscles have to work hard to keep the curve maintained in the spinal area. 

If we summarise the above discussion, we may conclude that the hip flexors, along with quadricep muscles, play an active role in pulling the body a step further towards the thigh. The abdominal muscles (rectus abdominis) acts as stabilizing muscles to maintain the posture of the upper body.


? Pro-Tip-


The people who have weak abdominal muscles, should not go for sit-ups. Instead, they should try for other variations of the sit-up exercise along with other abdominal workouts.

The resistance bands can also come handy to assist you while doing sit-ups. For tough guys who have been training for a few years, resistance bands can also be used to make this exercise even harder.

? For more details/insights into the mistakes, we do unintentionally while doing sit-ups, along with the exact step-by-step instructions for doing sit-ups with resistance bands. Do visit this article- Correct Ways To Do Sit-Ups With Resistance Bands – Assisted | Resisted.


My final words- 

I love the way body engages skeleton bones and muscles to produce the movements with few triggers through our brain.


Such behind the scene working of muscles and bones not only surprises us but also takes muscle-mind connection during the workout to a new level.

When we know exactly how the muscles behave during the range of motion, we learn to listen to our bodies and adjust workouts to avoid injuries.



If you do not have enough abdominal strength, avoid sit-up exercises for few months and focus on strengthening and stretching the flexors, abdominal muscles, and the quadriceps through several other isolated exercises like crunches, leg extension, leg raise, et cetera. 

Adding resistance bands for assistance during the learning phase of sit-ups can be an excellent method to grasp the technique without injuring the backbone of the body.

? To learn more about the potential of resistance bands in doing sit-ups and several other exercises right within the home premises, visit this fantastic article – Benefits of Resistance Bands – With Unique Visual Insights.




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