The biceps femoris muscle is located at the back of the thigh and forms part of the hamstring group of muscles. There are two parts to the biceps femoris and only one of these is included as part of the hamstrings. This part of the muscle is known as the long head. The short head part of the muscle starts on the outer hip. Primarily, both heads of the biceps femoris muscle help to flex the knee.
The two heads of the muscle differ in origin. The long head starts toward the bottom of the lower back and joins via a tendon, which it shares with another muscle called the semitendinosus. This is known as the long head as the point of attachment is much higher and further away from the insertion than the short head. Another purpose of the long head biceps femoris is to laterally rotate the hip when there is flexion of the knee.
In contrast to the long head, the short head attaches to the thigh bone. It therefore is much shorter than the long head although it still provides the same function — flexion of the knee joint. Both the long head and short head insert at the same tendon on the lateral side of the knee.
The biceps femoris muscle forms part of one of the largest muscle groups in the body — the hamstrings. Generally the name hamstrings is given to any of the three muscles located on the back of the thigh but is also used to describe tendons in the same location. The other two muscles that make up the hamstrings are the semiteninosus and semimembranosus.
Hamstring injuries are common among athletes due to the large amount of strain that can be transmitted through this muscle. Injuries are often more common in tall people who have naturally tight hamstring muscles. Hamstring injuries are notorious for being difficult to overcome as it can be hard to avoid re-injuring the muscle during day-to-day activities.
One of the most effective ways of avoiding hamstring muscle tears is to regularly stretch the muscles. This can be performed in a number of different ways although the stretcher should be careful to avoid overstretching. An example of a hamstring stretch is to use a towel or long exercise band to raise up the straight leg while lying in a supine position. Stretches should be held for a minimum of 20 seconds.