The hamstrings are located on the back of the thigh just under the gluteus maximus. There are three muscles that make up the hamstring muscle group: biceps femoris, semimembranous and semitendinous. Taken together, this muscle group assists in flexing the knee, extending the hip and decelerating while running and walking.
Biceps Femoris
The biceps femoris contains two heads: short and long. The biceps femoris is located on the outer back thigh. The long head of the biceps femoris originates from the ischial tuberosity, which is the part of the hip bone that often aches after sitting on hard surfaces for long periods. The short head originates on the upper inner portion of the femur called the supracondylar line. Both long and short heads of the bicep femoris come together across the back of the knee and attach to the head of the fibula.
Semimembranous
The semimembranous is located between the semitendinous and biceps femoris. The semimembranous also originates on the ischial tuberosity. This muscle extends down the inner thigh and attaches to the back portion of the medial condyle of the tibia. This muscle is called semimembranous for its upper one-third portion, or origination, consisting of membranous tissue.
Semitendinous
The semitendinous rests next to the semimembranous and originates on the ischial tuberosity of the hip. The semitendinous travels down the back of the femur, and its long rounded tendon attaches to the front of the medial condyle of the tibia. You can feel the semitendionous during knee flexion by placing your hand behind the inner part of your knee.
Actions
The hamstring group extends the hip and flexes the knee. Each muscle has one or more actions. The biceps femoris is involved with flexing and laterally rotating the lower leg at the knee and externally rotating the hip. Both semimembranous and semitendinous flex and medially rotate the lower leg at the knee, and also internally rotate the hip
Hamstring Strains
Hamstring strains typically occur in running or sports like soccer. The hamstring becomes overstretched and cannot handle the load placed on it. Some factors that can cause hamstring strains are inflexibility of the muscle group, muscle imbalance and fatigue.
References
- "Primary Anatomy"; John V. Basmajian; 1998
- AAOS: Hamstring muscle injuries
