Video: Overview of the muscles of lower limb

Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial on muscles of the lower limb. In today's tutorial, we'll be looking at the muscles of the lower limb and their functions. The lower limbs are built for support and propulsion. The muscles of the lower limb along with the muscle of the hip and gluteal regions counteract the load imposed on the lower extremity by supporting the whole body weight. These muscles also help maintain balance and stability.

There are many ways that muscles of the lower extremity can be classified either according to innervation, origin, function or topography. In this tutorial, we have classified the muscles according to regions and functional groups. The regions we're going to look at include the hip and gluteal region, the thigh, the leg and the foot. Now, generally, when talking about the lower limb, we might be inclined to use the term leg but we must be very careful when using this term as in human anatomy it refers to this region here. The leg does not refer to the entirety of the lower limb but only the portion between the knee joint and the ankle joint.

First we'll start by having a look at the muscles of the hip and gluteal region. These muscles are powerful movers and stabilizers of the femur during motion. The muscles of the hip can be divided into the muscles of the inner hip and the muscles of the outer hip. So let's start with the muscles of the inner hip. The first muscle we'll look at is the psoas major muscle which we can see here highlighted in green. This muscle is a stabilizer and flexor of the hip joint as well as a lateral flexor of the trunk.

The next muscle of the inner hip is the psoas minor muscle which contributes to the stabilization of the pelvis and the hip joint. In this illustration, we can see that psoas minor is located anterior to psoas major. The final muscle of the inner hip is the iliacus muscle which is the most powerful flexor of the hip joint. This muscle also plays a role in the overall stabilization and movement of the pelvis. It's important to note that the iliacus and the psoas major muscle act in union as the iliopsoas muscle to flex the hip joint.

Next let's have a look at the muscles of the outer hip. The first muscle we'll look at is the gluteus maximus which is the most powerful extensor and external rotator of the hip joint. The next two muscles we'll look at are the gluteus medius and the gluteus minimus. These muscles are the most powerful abductors and internal rotators of the hip joint. Another muscle of the outer hip is the tensor fascia latae which we can see here highlighted in green. This muscle facilitates abduction, flexion and internal rotation of the hip joint. Next we have the piriformis muscle which is another stabilizer of the hip joint followed by the obturator internus muscle which is an external rotator of the hip joint.

The next two muscles we're going to look are the gemelli muscles. First, we have the superior gemellus which we can see here followed by the inferior gemellus which we can see here. These muscles also act to stabilize the hip joint. The final muscle of the outer hip is the quadratus femoris muscle. This muscle is also a stabilizer of the hip joint. The piriformis, obturator internus, gemellus superior and inferior, and the quadratus femoris muscles are posterior muscles of the hip that work together to stabilize the pelvis and facilitate external rotation of the hip joint.

Although the adductor group of muscles are classified as hip muscles, these muscles are actually located on the medial side of the thigh. The first adductor muscle we'll look at is the obturator externus muscle. This muscle stabilizes the pelvis in the sagittal plane as well as facilitating adduction and external rotation of the hip joint. Next we have the pectineus muscle which we can see here highlighted in green. This muscle stabilizes the pelvis in the coronal plane and facilitates the adduction and external rotation of the hip joint as well as slight flexion.

Another muscle in this group is the adductor longus muscle. This muscle facilitates adduction and flexion of the hip joint as well as stabilizing the pelvis. Above adductor longus, we have adductor brevis. This muscle also facilitates adduction and flexion of the hip joint and stabilizes the pelvis. Next we have adductor magnus which not only facilitates adduction but also extension and external rotation of the hip joint along with stabilizing the pelvis. Then we have adductor minimus which facilitates slight flexion of the hip joint along with adduction and external rotation. Finally, we have the gracilis muscle which as you can see here is the most medially located muscle. This muscle facilitates the adduction and flexion of the hip joint and the flexion and internal rotation of the knee joint. So although these muscles are found in the thigh region, they are classed as hip muscles for functional reasons, that is, they mainly act on the hip joint.

Next we'll look at the muscles of the thigh which are divided into anterior and posterior thigh muscles. First, we'll look at the anterior muscles of the thigh starting with the sartorius muscle. This muscle is a flexor, abductor and external rotator of the hip joint and a flexor and internal rotator of the knee joint. As we can see in this illustration, the sartorius muscle runs lateral to medial as it crosses the anterior compartment of the thigh.

The next muscle we're going to look at is the quadriceps femoris muscle which is comprised of several muscles. The first is the rectus femoris muscle which facilitates flexion of the hip joint. Next is the vastus medialis muscle followed by the vastus intermedius muscle and the vastus lateralis muscle. All four parts of the quadriceps femoris muscle act to facilitate extension of the knee joint.

Now let's move on to the muscles of the posterior compartment. The first of which is the biceps femoris muscle which we can see here highlighted in green. This muscle extends the hip and stabilizes the pelvis in the sagittal plane and facilitates flexion and external rotation of the knee joint. Medial to the biceps femoris muscle, we have the semimembranosus muscle. This muscle facilitates flexion and internal rotation of the knee joint as well as extending the hip and stabilizing the pelvis. And, finally, we have the semitendinosus muscle which extends the hip, stabilizes the pelvis and facilitates flexion and internal rotation at the knee joint. These three flexor muscles of the posterior thigh are commonly referred to as the hamstring muscles.

Now let's look at the muscles of the leg which can be divided into the muscles of the anterior compartment, the lateral compartment and the posterior compartment. First we'll look at the muscles of the anterior compartment starting with tibialis anterior. This muscle facilitates dorsiflexion of the foot at the ankle joint. It also causes weak inversion. Next we have the extensor digitorum longus muscle which, along with facilitating dorsiflexion of the foot, also causes powerful eversion or pronation at the subtalar joint and extension of the metatarsophalangeal and interphalangeal joints of the second to fifth toes. Please note that the subtalar joint is the joint between the talus and the calcaneus. The metatarsophalangeal joints refer to the joints between the metatarsals and phalanges of the foot whereas the interphalangeal joints refer to the joints between the phalanges.

Finally, we have the extensor hallucis longus muscle which facilitates dorsiflexion of the foot. It also facilitates eversion and inversion depending on the initial position of the foot as well as extension of the metatarsophalangeal and interphalangeal joints of the big toe.

Before we continue, I'd like to mention that we'll cover several muscles containing the term "hallucis". This refers to hallux which is Latin for big toe. Therefore, if a muscle has hallucis in its name, then it must facilitate movement of the big toe.

So now let's move on to the lateral compartment of the leg where we can see two muscles. The first is fibularis longus which we can see here highlighted in green. This muscle facilitates plantarflexion and eversion or pronation of the foot as well as supporting the transverse arch of the foot. The second muscle of the lateral compartment is fibularis brevis which also facilitates plantarflexion and eversion or pronation of the foot.

So far we've looked at the muscles of the anterior and lateral compartments of the leg. Let's now look at the muscles of the posterior compartment. These muscles can be further divided into superficial and deep muscles. The superficial muscles of the leg are the triceps surae and the plantaris muscles. The triceps surae is a three-headed muscle and is composed of the soleus muscle which we can see here and the gastrocnemius muscle.

As we can see in this illustration, the gastrocnemius muscle is superficial to the soleus muscle. These muscles both end in a common tendon which is known as the Achilles tendon that attaches to the posterior calcaneus. The triceps surae muscle facilitates plantarflexion at the upper ankle joint and inversion at the subtalar joint. The gastrocnemius contributes to a small extent during flexion at the knee joint. The function of the plantaris muscle which we can see here is somewhat negligible, however, it may help to prevent compression of the muscles of the posterior compartment of the leg during knee flexion.

The next group of muscles of the posterior compartment we'll look at are the deep muscles. The first muscle we'll look at is the tibialis posterior muscle which facilitates plantarflexion and inversion of the foot. It also acts to support the transverse and longitudinal arches of the foot. Next we have the flexor digitorum longus muscle which also facilitates plantarflexion and inversion of the foot. This muscle also facilitates plantarflexion at the metatarsophalangeal and interphalangeal joints of the second to fifth toes.

Another deep muscle of the posterior compartment is the flexor hallucis longus which we can see here highlighted in green. This muscle supports the medial longitudinal arch of the foot, facilitates plantarflexion and inversion of the foot, and plantarflexion of the metatarsophalangeal and interphalangeal joints of the big toe. The last muscle of the posterior compartment is the popliteus muscle. This muscle stabilizes the knee joint and facilities flexion and internal rotation at this joint.

Now let's move on to look at the muscles of the foot which can be divided into dorsal and plantar muscles of the foot. We'll start with the dorsal muscles of the foot. The first of which is the extensor digitorum brevis muscle. This muscle facilitates extension of the metatarsophalangeal joints and the proximal interphalangeal joints of the second to fourth toes. The other dorsal muscle of the foot is the extensor hallucis brevis muscle. This muscle facilitates extension at the metatarsophalangeal joint of the big toe.

Now that we've discussed the dorsal muscles of the foot, let's go on to look at the plantar muscles of the foot. These muscles can be further divided into the medial, lateral and central muscles of the foot. On the medial aspect of the sole of the foot, we have the abductor hallucis muscle. This muscle acts to facilitate flexion and medial abduction of the big toe as well as supporting the longitudinal arch. Next, we have the adductor hallucis muscle which as you might guess adducts the big toe. It also flexes the first metatarsophalangeal joint. The transverse head of this muscle supports the transverse arch of the foot while the oblique head supports the longitudinal arch. Finally, we have the flexor hallucis brevis muscle which flexes the metatarsophalangeal joint of the big toe.

Let's move on to the lateral aspect of the sole of the foot. The first muscle is the abductor digiti minimi muscle. This muscle facilitates flexion of the metatarsophalangeal joint of the little toe and abducts the little toe. Next we have flexor digiti minimi brevis. This muscle facilitates flexion of the metatarsophalangeal joint of the little toe. Finally, we have the opponens digiti minimi brevis muscle – a muscle which is not found in all human bodies.

Now let's look at the central aspect of the sole of the foot. First we have the flexor digitorum brevis muscle. This muscle facilitates flexion of the metatarsophalangeal and the proximal interphalangeal joints of the second to fifth toes. It also supports the longitudinal arch of the foot. The next muscle we'll look at is the quadratus plantae muscle. This muscle doesn't move any joints but instead redirects and augments the pull of the flexor digitorum longus muscle increasing the effectiveness of the plantarflexion of this muscle.

Next we have the lumbrical muscles of the second to fifth digits. These muscles facilitate flexion of the metatarsophalangeal joints of the second to fifth toe. They also facilitate extension of the interphalangeal joints of these toes and the adduction of these toes towards the big toe. Then we have the plantar interossei muscles of the third to fifth digits. These muscles facilitate flexion of the metatarsophalangeal joints of the third, fourth and fifth toes. They also facilitate extension of the interphalangeal joints of the third to fifth toes and abduction of these toes towards the second toe.

Finally, we have the dorsal interossei muscles of the second to forth digits. These muscles facilitate flexion at the metatarsophalangeal joints of the second to fourth toes. They also facilitate extension at the interphalangeal joints of these toes as well as abduction of the third and fourth toes away from the second toe.

Now that we've discussed the muscles of the foot, that brings us to the end of this tutorial on muscles of the lower limb. I hope you enjoyed it and thank you for listening.

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