Categories:

The Posterior Compartment: Gastrocnemius, Soleus, And The Plantaris

Gastrocnemius And Soleus Muscles

Our lower leg muscles often don’t get as much attention as the quadriceps and hamstrings of our thigh. That is, they don’t get our attention until something starts to hurt. But we use these muscles for running, jumping, walking, and for simply standing upright. In this article, let’s take a look at our posterior lower leg muscles, their attachments, and their actions.

What is the posterior compartment?

The lower leg is typically divided into three main muscular compartments. Those are the anterior, lateral, and posterior compartments. Sometimes anatomists include a fourth compartment. They divide the posterior compartment into the superficial and deep posterior compartments. Those compartments are divided structurally by intermuscular septa. Those are areas of fascia between the muscles. The superficial posterior compartment is the section of the back of the lower leg that is closer to the surface. It’s separated from the deep posterior compartment by the posterior intermuscular septum.

What are the key muscles of the posterior compartment?

The muscles of the superior posterior compartment form what we think of as our “calf muscles.” The main muscles that the compartment includes are the gastrocnemius and soleus muscles. There is also a small, thin muscle called plantaris that is part of this section. However, it’s very small, mostly tendinous, and absent in about 10% of the population. When anatomists reference to this group of muscles, they sometimes refer to them as the “triceps surae.” This is a more technical name for the group of these three muscles.

Muscle attachments

Gastrocnemius

The gastrocnemius is the most superficial of the muscles in the posterior compartment of the leg. At the proximal (top) end, it has two heads. The medial head attaches to the medial condyle of the femur (the thigh bone). The lateral head attaches to the lateral condyle of the femur. From there the two heads join to become one muscle. At the distal end, they become the Achilles tendon, which attaches to the heel bone (called the calcaneus).

Soleus

The Soleus is located deep to (underneath) the gastrocnemius. At its proximal end, it attaches to a bony ridge called the “soleal line” on the tibia and to the proximal end of the fibula (the smaller of the two leg bones). At its distal (lower) end, it joins with gastrocnemius to become the Achilles tendon which attaches to the calcaneus.

Plantaris

The small plantaris attaches at its proximal end to a bony ridge on the femur called the supracondylar line. The tendinous portion of this muscle then runs between the gastrocnemius and soleus. It joins those two muscles at its distal end to become part of the Achilles tendon and attach to the calcaneus.

Muscle actions

The gastrocnemius crosses two joints. It crosses and acts on both the knee and ankle joints. At the proximal end, the gastrocnemius could be thought of as “holding hands” with the lower fibers of the hamstrings. They work together to flex the knee joint. At its distal end, it works with the soleus to do plantarflexion of the foot at the ankle. 

In functional movement, one job of the gastrocnemius and soleus muscles is to work with the quadriceps to coordinate our leg and foot movements during the swing phase of gait. They also help maintain our static posture when we’re standing. The little plantaris crosses both the knee and ankle joints as well. If it’s present, it assists in both flexion of the knee and plantarflexion of the foot at the ankle.

Conclusion

Our posterior lower leg muscles are an important group for running, jumping, and walking. They’re important muscles for creating power behind those movements, particularly when we’re going uphill. They sometimes get overshadowed by the more popular thigh muscles, like our quadriceps and hamstrings. But, they’re just as important. In this article, we reviewed their location, attachments, and actions.

References

Bordoni B. and M. Varacallo. 2023. Anatomy, Bony Pelvis and Lower Limb, Gastrocnemius Muscle. [Updated 2023 Apr 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532946/

Myers, T., 2014. ‘Calf x Fascia: The compartments of the lower leg’ In The Anatomist’s Corner: Issues in Structural Anatomy. Pgs.171-177.

Latest Posts