Biceps femorisSemitendinosusSemimembranosus
The hamstring muscles are important for standing, walking, running, and jumping. Common problems that involve the hamstrings are strained muscles, flatback syndrome, spinal disc injury, and sacroiliac (SI) joint dysfunction.
This article covers the anatomy of the hamstring muscles, their functions, common injuries, and how they’re treated.
While the hamstrings can produce both movements at the same time, they can’t do so to their full capacity. It’s one movement or the other if you’re looking to go all the way with a hamstring muscle contraction.
The biceps femoris has two heads—a long and a short. At the hip, both the long and short heads rotate the thigh outwardly and extend it backward. At the knee, they flex and laterally rotate the joint. Of all the hamstring muscles, the biceps femoris is the biggest contributor to hip extension.
The long head of the biceps femoris originates on the inner side of your sitting bones, which are little knobs of bone that are technically called the ischial tuberosities. The ischial tuberosities are located on the underside of your pelvis. (You likely can feel them when you sit down.)
The short head of the biceps femoris originates on three places on the femur (i.e., your thigh bone) that are located more towards your knee than your hip. Note that the short head of the biceps femoris is the only part of the hamstring muscle group that does not cross two joints. For this reason, some experts don’t consider it to be a hamstring muscle at all. It’s actually missing in some people.
Both the long and short head of the biceps attach on the lower leg, also in three places: The head of the fibula bone, the outer (called lateral) condyle of the tibia bone, and the fascia of the leg. The multitude of attachment sites on the lower leg may make for more tears here than in the other hamstring muscles.
As with the other hamstring muscles, the semitendinosus muscle crosses the knee. It attaches at the upper part of your tibia bone (the shin bone) on the inner, or medial side. It also attaches on the deep fascia of the leg. The semitendinosus, along with the satorius and gracilis muscles, is one of three muscles that come together to form the pes anserine tendon that terminates on the anteromedial (the area to the front and side of the tibia).
Although many anatomy books don’t show this, the semitendinosus is divided into two sections by a visible ridge of tendonous tissue called a raphe.
At the hip, the semidendinosus extends the thigh back and also helps or assists with medial rotation of the thigh. At the knee, this muscle bends and medially rotates the joint.
At the hip, the semimembranosus extends the joint, and helps with medial rotation (i.e., turning the lower extremity inward). It also flexes the and medially rotates the knee.
Flatback syndrome Spinal disc injury SI joint dysfunction Strained muscles
Flatback Syndrome
If you look at a spine from the side, you should see two curves—a backward curve (lordosis) where it connects to the pelvic bone, and a forward curve (kyphosis) where it connects to the ribs.
In flatback syndrome, you lose one or both curves. In cases involving lordosis, a possible cause is tight hamstring muscles that keep the pelvis tilted too far forward.
This interferes with a healthy posture, can make it difficult to walk and perform other basic tasks, and cause significant pain.
Treatment for flatback syndrome may involve:
Exercises/physical therapyPain medicationEpidural steroid injectionsSurgery
Spinal Disc Injury
As with flatback syndrome, tight hamstring muscles that alter the tilt of your pelvic bone can cause painful problems with your spinal discs. This happens because the change in angles causes too heavy a load on some discs.
The result can be:
Herniated disc Degenerative disc disease (DDD)
Treatments for a herniated disc and DDD may include:
Temporarily decreasing activity Anti-inflammatory medications Epidural steroid injections Physical therapy Surgery, if other treatments fail
Sacroiliac Joint Dysfunction
The SI joints are small, relatively inflexible joints at the base of your spine. Their main purposes are to provide stability and transfer your weight from one leg to the other when you walk.
Tight hamstrings can cause this by putting undue strain on the area. Treatment typically involves:
Physical therapyChiropractic adjustmentsAnti-inflammatory medications
Strained Hamstring Muscle
Hamstring muscle injuries are often caused by muscle overload, which is when the muscle is stretched too far or suddenly takes on too high a load. This is often the result of an activity such as sprinting.
Treatment for strained hamstring muscles is often:
RICE (rest, ice, compression, elevation)Immobilization (splint or brace)Physical therapySurgery
