Sunday, March 21, 2010

Hamstring strains

Hamstrings strains are a very common running injury. These can be serious injuries, slow to heal. Nearly one third of these injuries return in the first year. The high chance for re-injury may be the result of the failure to identify several factors such as the underlying muscle imbalances, weakness, mobility and faulty movement patterns.


The hamstring consists of the semimembranosus, semitendinosus, and the biceps femoris muscles. The long head of the biceps femoris is the most often injured.
These muscles originate at the back side of the pelvis off of the ischial tuberosity. The ischial tuberosity is the part of the pelvis that we sit on. The semimembranosus, semitendinosus insert on the inside of the lower leg and the biceps femoris inserts on the outside of the lower leg.

Function and mechanisms of injury:

When most of us think of the hamstring function we think hamstring curl or bending the knee to bring the foot toward the buttocks (knee flexion) and bringing the thigh backwards (hip extension). However, with movement (walking and running) the hamstring primary function is not knee flexion. Think of the hamstring in terms as reigns of a horse. With movement, the primary function of the hamstring is to decelerate the lower leg as it swings forward. The hamstring is contracting but lengthening(eccentric contraction). This is when most hamstring injuries occur with running. In other words, the hamstring is not strong enough to handle the velocity of the lower leg before the next heel strike.

Other severe injuries, such as partial or full ruptures, may occur with sudden hip flexion with the knee extended. This commonly happens with water skiing when the skier falls forward over the skis. Dancers, yoga enthusiasts and gymnasts also often rupture the hamstring with an extreme stretch.

Signs and symptoms:

When a hamstring is injured a "grabbing" sensation is felt, followed by pain, which may limit activity. A normal stride may not be possible. When the injury is near the ischial tuberosity (sit bone)it usually indicates a severe injury which is very slow to heal. With sitting the injured hamstring will tighten up and often body weight is shifted off the injured side. If excessive ecchymosis (bruising), severe tenderness to touch and significant loss of range of motion are present, the hamstring may be fully or partially ruptured. However, even in the absence of these signs, hamstring strains are very difficult to heal and shouldn’t be taken lightly. Even after rest, normal everyday activities such as kneeling, squatting and walking may be limited and may easily re-strain the hamstring.

Risk factors:

Age and prior history of hamstring injuries
Hamstring eccentric weakness with fatigue
Muscle imbalance
(very strong quadriceps to weak eccentric hamstring and glutes)
Lack of mobility
Hip flexor tightness with lower abdominal weakness

In my next post I will discuss the recovery process.

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