Knee Function: Posterior Muscles

This week I’m writing about the anatomy and function of the knee. Today I’m writing about the posterior knee muscles.

There are more posterior muscles in the knee than in the anterior. Four muscles cross the hip and knee, while two cross the knee and ankle. They include both large, powerful muscles as well as small, weak muscles.

Biceps Femoris

The biceps femoris is the hamstring muscle.

The short head of the muscle is a knee flexor. This is the semimembranosus. The long head (which crosses both the knee and hip joint), is both a knee flexor and hip extensor. This is the semitendinosus.


The sartorius runs diagonally across the thigh and is the longest muscle in the human body. It has four movement functions: Three occur at the hip while one occurs at the knee.


This is a deep and very small muscle that attaches to the tibia and crosses the back of the knee. Given its size, it is a weak knee flexor.

The main benefit to the popleitis is that it draws the meniscus back, thus preventing pinching between the tibia and femur.


The plantaris has little power and is actually absent in 10 percent of the human population. Its primary function is knee flexion, but can also be a plantar flexor.

For interesting research on this muscle, see this: Plantaris in the mouse and rat.


The gastrocnemius is the calf muscle. It helps both the knee and ankle function properly.



AMRAP 12:00
10 Alternating Chair (or Box Step Ups)
20 Alternating Leg V-Ups
40 Plate Hops (or Line Hops)

Other Articles In This Series:
1. Knee Function: Four Bones, Two Directions
2. Knee Function: Anterior Muscles
3. Knee Function: Posterior Muscles

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