What Is a Hamstring Muscle?

The hamstring muscle group makes up the back of the upper leg. It is sometimes referred to as the leg biceps because its curling action is similar to the biceps of the upper arm.

Actions

The hamstring extends the thigh, flexes the knee and medially rotates the leg.
Hamstrings are comprised of three muscles.

Biceps femoris

The most lateral (outside) of the three originates at the ischial tuberosity and inserts into the head of the femur and lateral condyle of the tibia.

Semitendinosus

Positioned medially (inside) the biceps femoris, it originates in the ischial tuberosity and inserts in the medial condyle of the tibia.

Semimembranosus

Inside and under the semitendinosus, it originates in the ischial tuberosity and inserts into the medial condyle of the tibia.

Trivia

The name hamstrings refers to the old butcher's practice of hanging hams while they were smoked.
A pulled hamstring, a common athletic injury, is due to muscle imbalance because the hamstrings are often weak compared to the opposing thigh muscles.

References

• Human Anatomy and Physiology seventh edition c 2007 Elaine m. Marieb and Katja Hoehn