Did you know the thigh is the part of the lower appendage proximal to the knee? The muscles of the thigh move the leg at the knee. This lesson will identify the major muscles involved in flexion and extension of the leg at the knee, including the hamstrings and quadriceps femoris groups.

Thigh Muscles

I grew up playing backyard football. It was great fun and certainly a lot of exercise. Every now and then, my buddy would pull the ball away just as I was about to kick it. Sound familiar? I would get mad and everyone would laugh as I fell on my backside. Among others, we will discuss the muscles used to kick that football in this lesson.

The two groups of the large thigh muscles
Thigh Muscle Types

It is anatomically correct to refer to that part of the lower appendage proximal to the knee as the thigh and distal to the knee as the leg. In general, muscles located in the hip region will move the thigh, and muscles located in the thigh will move the leg. Most of the thigh muscles are contained within two large groups of muscles referred to as the quads, which extend the leg at the knee and the hamstrings, which flex the leg at the knee. These muscles are innervated by the sciatic, femoral, and tibial nerves. Sciatica is a condition resulting from compression of the sciatic nerve. A person experiences lower back pain, leg pain, and leg weakness in association with sciatica.

Leg Flexors

We did what we called butt kicks in track practice to get faster. This exercise required us to flex our legs so our heels would actually kick our buttocks.

The semitendinosus is medial to the biceps femoris.
semitendinosus

Let’s start with the hamstrings group. The hamstrings group is composed of three muscles, all of which produce flexion of the leg. These muscles are located in the posterior compartment of the thigh, which is the back side. The biceps femoris is a double-headed muscle, hence the prefix bi. The long head originates from the pelvic girdle, while the short head originates from the femur. Both heads insert on the fibula and tibia of the leg.

If we look medial to the biceps femoris, we can see what we call the semitendinosus, which originates from the posterior pelvic girdle and inserts on the tibia. Deep to the semitendinosus, we can see the semimembranosus, which originates from the pelvic girdle and inserts on the tibia as well. Here’s a hint to help remember the names: the semimembranosus is broad like a membrane, while the semitendinosus is narrow like a tendon.

The anterior location of the sartorius muscle in the thigh
Satorius Muscle

In addition to the three hamstrings, which we just talked about, the sartorius muscle helps to flex the leg as well. The sartorius is unique in that it is located on the anterior surface of the thigh, as opposed to the back side. This muscle originates from the anterior-superior iliac spine, runs at an angle across the thigh and inserts on the medial surface of the tibia. Now, what about this anterior-superior iliac spine? You can actually feel it if you take your thumb and press it up against the front side of your hip. That point right there is the anterior-superior iliac spine. Due to its attachment, the sartorius flexes the leg at the knee and laterally rotates the thigh. This happens when we cross our legs.

Leg Extensors

Now, let’s move on to leg extensors. My daughter loves to play soccer. Let’s take a look at some of the muscles she uses when she kicks the ball. She extends her leg at the knee as she drives in a goal for a score. The quads, or quadriceps femoris, are a group of four muscles responsible for extension of the leg at the knee. These muscles are located in the anterior compartment of the thigh, and they’re deep to the sartorius, which we just talked about.

The patellar ligament connects the patella to the tibia.
Patellar Ligament

The rectus femoris originates from the anterior-superior iliac spine and inserts on the tibia via what we call the patellar ligament. Now, let’s stop here for a minute. Recall that a ligament attaches bone to another bone, whereas a tendon attaches muscle to a bone. So, the patellar ligament attaches the patella to the tibia. Rectus means straight and femoris refers to the femur, which helps us to remember this muscle’s fiber arrangement and its location.

A collection of three vastus muscles originates from the femur and insert on the tibia via the patellar ligament as well. These muscles are named vast because they attach along much of the femur’s length. Medial to the rectus femoris, we can see the vastus medialis, lateral to the rectus femoris is the vastus lateralis. Make sense? Deep to the rectus femoris, between the vastus medialis and lateralis, we can see the vastus intermedius, which I think makes sense as well.

The vastus intermedius is between the vastus medialis and vastus lateralis.
vastus intermedius

Lesson Summary

In summary, most muscles in the anterior compartment of the thigh extend the leg, while muscles in the posterior compartment of the thigh flex the leg. The hamstrings are leg flexors, and include three muscles located in the posterior compartment. They are the biceps femoris, semitendinosus and semimembranosus. In addition, the sartorius muscle in the anterior thigh helps to flex the leg. The quadriceps femoris, or quads, include four muscles in the anterior compartment that serve to extend the knee. The quads are made up of the rectus femoris, vastus medialis, vastus lateralis and finally the vastus intermedius.

Learning Outcomes

After this lesson, you’ll be able to:

  • Differentiate between the anterior and posterior thigh muscles, as well as between the leg and the thigh
  • List the muscles of the hamstrings and describe their function
  • List the muscles of the quadriceps femoris and describe their function
  • Explain the location and function of the sartorius