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What Muscles Are Included in the Hamstring & Quadriceps?

Overview

The two major muscle groups of the upper leg are the hamstrings and the quadriceps. The hamstring muscle group is in the back of the thigh. The quadriceps muscle group is the large bulk of muscle at the front of the thigh. The hamstrings are made up of three individual muscles, while the quadriceps is made up of four different muscles. These two muscle groups are antagonistic and you use them in nearly all ambulatory activities.

Biceps Femoris

The biceps femoris is a member of the hamstring muscle group. It is a large muscle that runs down the back and outside of the thigh. It runs from the pelvic bone all the way to the lower leg, crossing both the hip and knee joint. It is named “biceps” because it has two heads and “femoris” because it runs the length of the femur bone. The major action of the biceps femoris is to flex the lower leg.

Semitendinosus

The semitendinosus is another member of the hamstring muscle group. It runs down the middle back of the thigh. It runs from the pelvic bone all the way to the lower leg crossing both the hip and knee joint. It receives its name from the fact that it has a long tendon that attaches the belly of the muscle to the lower leg. The major action of the semitendinosus is to flex the lower leg.

Semimembranosus

The semimembranosus is the third member of the hamstring muscle group. It is a muscle that runs down the back and inner portion of the thigh. It runs from the pelvic bone all the way to the lower leg crossing both the hip and knee joint. It is called the semimembranosus because the muscle is wrapped in a membrane that connects it to its sibling, the semitendinosus. The major action of the semimembranosus is to flex the lower leg.

Rectus Femoris

The rectus femoris is a member of the quadriceps muscle group. It is a straight muscle that runs down the middle of the front of the thigh from the pelvic bone all the way to the lower leg crossing both the hip and knee joint. The term “rectus” refers to the straight shape of the muscle while the term “femoris” describes the fact that the muscle runs the length of the femur bone. The major action of the rectus femoris is to extend the lower leg but it also is responsible for hip flexion.

Vastus Lateralis

The vastus lateralis is a wide muscle that is part of the quadriceps muscle group. It runs down the front and outside of the thigh from the femur to the lower leg crossing only the knee joint. It is named “vastus” because it vast or wide and “lateralis” because it is the most lateral or outside of all the quadriceps muscles. The major action of the vastus lateralis is to extend the lower leg.

Vastus Medialis

The vastus medialis is another member of the quadriceps muscle group. This wide muscle runs down the front and inside of the thigh from the femur to the lower leg crossing only the knee joint. It is named “vastus” because it vast or wide and “medialis” because it is medial or to the inside of the leg. The major action of the vastus medialis is to extend the lower leg.

Vastus Intermedius

The vastus intermedius is the fourth member of the quadriceps muscle group. It is a wide muscle running down the middle of the thigh and under the rectus femoris. It extends from the femur to the lower leg crossing only the knee joint. It is named “vastus” because it vast or wide and “intermedius” because it is intermediate or in between of the other two vastus muscles. The major action of the vastus intermedius is to extend the lower leg.

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This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.