Hamstring

What is the Hamstring Muscle Group

The hamstring is a group of three muscles in the posterior compartment of the thigh, located between the hip and knee joints. These muscles play a vital role in the movements of the lower limb.

The term “hamstrings” comes from Old English “ham,” meaning the bend of the knee, and “string,” referring to the tendons at the back of the knee. All three muscles are attached to the knee joint via long, thin tendons.

Characteristics of the Hamstring Muscles

All hamstring muscles have several common  structural and functional characteristics, including:

• They originate from the ischial tuberosity
• They cross both the hip and knee joints
• They are innervated by the tibial division of the sciatic nerve
• They insert into the tibia and/or fibula
• Their function includes extending the hip and flexing the knee

Names of the Hamstring Muscles With Location & Anatomy

Here is a list of the muscles that make up the hamstring group, along with their locations in the posterior thigh and basic anatomical details. From lateral to medial, the hamstring muscles are:

Name	Origin	Insertion	Innervation	Blood Supply
Biceps femoris
— Long head	Lower inner surface of the ischial tuberosity	— Lateral surface of the proximal fibula — Lateral tibial condyle	Tibial nerve (L5-S2)	Perforating, inferior gluteal, and popliteal arteries
— Short head	Linea aspera, and lateral supracondylar line of the femur	Same as the long head	Common fibular nerve (L4-S3)	Perforating arteries
Semitendinosus	Same as the long head of biceps femoris, forming the conjoint tendon of the hamstring	Medial surface of the proximal tibia (via pes anserinus)	Tibial nerve (L5-S2)	Inferior gluteal and perforating arteries
Semimembranosus	Superior lateral surface of the ischial tuberosity	Posterior surface of the medial tibial condyle	Tibial nerve (L5-S2)	Perforating arteries

As shown in the table above, the short head of the biceps femoris lacks some characteristics of a true hamstring muscle. It has no attachment at the ischial tuberosity, meaning that it does not participate in hip extension. Additionally, it has a different source of innervation from the common fibular nerve. As a result, the short head of biceps femoris is often excluded from the group of true hamstrings.

The “hamstring part” of the adductor magnus also originates from the ischial tuberosity. However, it inserts into the adductor tubercle of the femur instead of crossing the knee joint. As a result, it does not assist in knee flexion and is not considered a true hamstring muscle.

Functions of the Hamstring Muscles

As mentioned earlier, the hamstring muscles act on both the hip and knee joints. 

Extending the hip: With their attachment at the ischial tuberosity, when the hamstring muscles contract, they cause extension of the thigh at the hip joint. This action allows you to get out of a chair and stand straight.

Flexing the knee: The hamstrings insert onto the lower leg bones, the tibia and fibula, enabling them to flex the knee joint and bend the leg. This action makes them vital in everyday activities, including walking, running, climbing stairs, and jumping.

Rotating the knee: The long head of the biceps femoris assists in lateral (external) rotation of the tibia when the knee is flexed. The semitendinosus and semimembranosus assist in medial (internal) rotation of the tibia. These rotational actions are especially important during pivoting or changing direction, such as in sports like football or basketball.

These muscles also play an important role in stabilizing the knee joint.

The hamstrings are among the most commonly injured muscles in sports, especially those involving sprinting and sudden changes in direction, like soccer and track events. This is due to the high demands placed on the muscles during rapid hip extension and knee flexion.

Antagonists

The quadriceps muscle group, including the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis, is the primary antagonist of the hamstring muscles. It performs the opposite actions: extending the knee joint (opposing hamstring flexion) and flexing the hip joint (opposing hamstring extension).