The hamstrings are a muscle group located at the back of the thigh. Dysfunction in the hamstrings can affect the mechanics of the pelvis, lower back and knee. The hamstrings are divided into three distinct muscles; the biceps femoris which has both a long head and a short head, the semitendinosus, and the semimembranosus.
The top of the hamstrings attach to the ischial tuberosity, commonly known as the sit bone as it is the bony protrusion comprising part of the pelvis that we sit on. The long head of the biceps femoris is located on the outside of the posterior thigh and shares a common attachment point at the pelvis with the semitendinosus. The short head of the muscle attaches half way down the shaft of the thigh bone with the combined muscles predominately attaching to the head of the fibula as well as the back of the knee joint on the tibia. The majority of hamstring injuries occur in the biceps femoris, mainly at the muscle-tendon junction.
The semimembranosus travels down the inside part of the posterior thigh attaching to the tibia. The semitendinosus sits on top of the semimembranosus with its tendon wrapping around and attaching to the front of the knee. A portion of this tendon is commonly harvested and used as a graft in the reconstruction of an injured anterior cruciate ligament.
The hamstrings assist in both extending the hip joint and bending the knee. In addition to these movements the biceps femoris has the ability to laterally rotate the thigh and the two inside hamstrings can rotate the thigh inwards. Due to the hamstrings acting upon two joints concurrently, it is susceptible to injury. This is the case particularly in sports and activities that require a high degree of speed, acceleration, power, agility and kicking such as sprinting and the football codes.
Hamstring injuries account for approximately 15% of all injuries in the AFL and 12% of injuries in British football. Additionally, hamstring injuries have the highest recurrence rate of all injuries with a recurrence rate of 34% in AFL and 12% in British football. Risk factors for hamstring strains include previous injury to the area, an imbalance between quadriceps and hamstring strength, an imbalance between the strength of the hamstrings between legs, increasing age of participant, fatigue, and an inadequate warm up. Contrary to popular belief, there has been no correlation found between flexibility and the rate of hamstring injury occurrence.
During maximal sprinting, the hamstrings become highly active as they work to decelerate the swinging leg. At this point the hamstrings are maximally activated and are approaching peak length. It is at this point that the hamstrings are most at risk of failure. An appropriate strength training regime can prepare the hamstrings to cope with these explosive demands. In addition to correct exercise prescription, physiotherapy can help to address any scar tissue formation as a result of a recent hamstring strain, and assess if tightness or dysfunction in the hamstrings are affecting lower limb mechanics or contributing to low back pain.