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Functions and anatomy of the gracilis muscle shown with 3D model animation.
Hi everyone! This is Joao from Kenhub, and on this tutorial, we will look at the functions of the gracilis muscle, which is the one you can see now isolated on the screen. Before we begin talking about all the movements the gracilis is responsible for, let me show it to you more clearly and put this muscle into some context so you become more familiar with it.
Here is the gracilis muscle again but seen head-on from a medial view of the thigh. As you can see from its location, the gracilis is one of the seven muscles of the medial compartment of the thigh. Six of these muscles belong to what is known as the adductor group which is mainly responsible for, well, you guessed it, adduction of the thigh. Just to avoid any confusion, this is A-D-D, so adduction, and not A-B-D, abduction. It’s very easy to mix these two up.
This means that contraction of these muscles pulls the thigh medially bringing it closer to the midline of your body. Thanks to your adductors, you are able to cross your legs, remain balanced while walking, swim especially the breast stroke, and not accidentally split your legs when ice skating. That certainly sounds quite painful, so take a minute and thank your adductors for doing an amazing job.
Now let’s get back to the gracilis and find out more about it.
Here it is once again isolated on the screen, the gracilis through and through. As you know, a muscle can’t perform its functions without a proper nerve supply and the gracilis is no exception. This muscle is supplied by the obturator nerve which you can see highlighted in green on the screen. This nerve forms part of the lumbar plexus and arises from the second, third, and fourth lumbar segments.
The gracilis is the weakest member of the adductor group and the most superficial muscle of all of them. This means that it is closest to the surface of your body with no other muscles covering it. This aspect also makes it the most medial muscle of the thigh.
According to our friend here on the screen, the gracilis is a long strap-like muscle that originates from the inferior pubic ramus and joins the pes anserinus with the two other adductors. In turn, this common tendon inserts into the superior part of the medial surface of the tibia.
Let’s rotate the model so we can see the gracilis from the front, and here are the same attachments once again but seen from the frontal perspective – the inferior pubic ramus, the pes anserinus, and the superior part of the medial surface of the tibia.
Now that you’ve seen where the gracilis begins and ends, I am sure you can name the joints moved by this muscle. That’s right. There are not just one but two joints involved – the hip and the knee. The hip joint is a ball-and-socket joint capable of a large degree of movement and it is where the head of the femur meets the acetabulum of the pelvis. The knee is a hinged joint capable of limited movement and it is where the femur of the thigh and the tibia of the leg meet.
Now let’s take a closer look at the movements of the hip and knee joints that the gracilis is involved in.
It is involved in flexion and adduction of the thigh around the hip joint together with flexion and internal rotation of the knee – so four distinct movements altogether. As there are a quite a few of them, let’s take them one by one and use the model on the screen to visualize each movement.
The easiest way for you to see the first one which is thigh flexion is to tell our friend on the screen to perform an action that you are doing on a daily basis which is climbing stairs. When you take a step onto an elevated surface or over an obstacle, the adductor muscle group including the gracilis contracts allowing you to move your thigh as you see right now on the screen.
Let’s continue now with the second movement the gracilis is involved in around the hip joint. In order to see the second action the gracilis is responsible for, I’ll tell the model to abduct or raise its thigh laterally until an angle of forty-five degrees give or take. As you already know by now, the gracilis is part of the adductor group of the thigh, hence as the name suggests, when these muscles contract as you see now, the gracilis is involved in bringing the thigh closer to the center or midline of your body. This is known as thigh adduction and happens every time you cross your legs.
So there you have it, the two movements the gracilis muscle is involved in at the hip joint – adduction and flexion.
Now we’ll move on to the next set of movements which happen around the knee joint. I’ll move the model towards the left-hand side of the screen so you have a full view of the action and don’t miss anything. As you are aware by now, the gracilis inserts into the superior part of the medial surface of the tibia just below the knee, therefore, when the gracilis contracts as you can see now, the leg is brought backwards in a movement known as knee flexion.
It is important for you to note that the gracilis is not the sole flexor of the knee. It works in unison with other major knee flexors like the hamstring muscle group when performing this action.
Now we’ll take a look at the fourth and final movement that the gracilis is involved in. Now, bear with me. We’re almost, almost done here. The best way to see this action is to place the model in a sitting position and look at it directly from the front – like we see now. Hope he’s not too angry with us because we’re asking for him to move a lot. What you see now on the screen is what it would look like if you were sitting on a chair. When the knee is flexed like it is now, contraction of the gracilis leads to internal rotation of the lower leg which involves moving it towards the midline of your body.
So, there you have it – the functions of the gracilis muscle. Before we wrap up this tutorial, let’s quickly recap them and see the movements one more time since there are quite a few.
The gracilis acts on two joints – the hip and the knee – being capable of producing four movements in total – two at each joint. We saw that it is capable of producing thigh flexion by bringing your thigh up and in front of your body, similar to climbing a stair, and also thigh adduction by bringing the thigh closer to the midline of the body. We also learned that the gracilis takes part in knee flexion which involves bending the knee backwards and in internal rotation by moving the lower leg towards the midline of your body.
This is it for now. I hope you enjoyed learning about the functions of the gracilis muscle, and I will see you on the next tutorial.