Weakness of hamstring muscle produces a significant loss of knee flexion strength. Weakness in knee flexion in the erect posture produces little disability. However, weakness of the hamstrings may produce more functional impairment at the hips, where the hamstring muscles provide a substantial part of extension strength. The superimposed weight that creates a flexion moment at the knee during a squat produces a flexion moment at the hip. That flexion moment is resisted by a muscular extension moment generated at least in part by the hamstring muscles. Consequently, weakness of the hamstrings may result in significant difficulty in bending and lifting.

EFFECTS OF TIGHTNESS:-

Hamstring tightness is the inability to stretch the muscle through full range of amplitude. Muscle is a prime mover and stabilizer of body that contains muscle spindle, as its functional unit and golgi tendon organs plays important role in determining the length and function of muscular components. Hamstrings are the long and powerful group of muscle that span the back of the thigh. Tightness of this muscle can play a role in sport related injuries, lumbar spine disorder and general low back pain.

Hamstring tightness is a common condition found in both symptomatic and asymptomatic subjects. The hamstrings are example of muscle group that have a tendency to shorten (Turner et al,1988).Lack of hamstring flexibility was the single most important characteristics of hamstring injuries in athletes. Tightness of the hamstrings results in limitations in knee extension ROM when the hip is flexed. Large amount of hamstring tightness can produce knee flexion contractures, an inability to reach full knee extension. A tight hamstring causes increased patella femoral compressive force, which may eventually lead to patella femoral syndrome. Poor hamstrings flexibility has been associated with low back pain in cross- sectional studies in both adolescents and adults.

PREVALENCE OF HAMSTRING INJURIES

Prevalence ranges from 8 to 25 %, depending upon the sport. The timing for return to sport ranges from as early as two weeks to never, depending upon injury severity and the sport in question. One observational study reports a single-season prevalence rate greater than 50 percent among elite soccer players. Recurrent hamstring injuries develop in more than 30 percent of athletes, with most occurring during the ensuing sporting season. High incidence of hamstring muscle strains are associated with sports that involve stretch shortening cycle activities such as Sprinting, High-intensity Running, Stopping, Starting, Quick change of direction, Kicking.

Athletes with a history of hamstring injury have significantly less hamstring flexibility than their uninjured counterparts and are prone to reoccurrence of hamstring injuries. Therefore, the identification of simple therapeutic regimens capable of increasing hamstring flexibility may reduce the chance for injury of athletes with low levels of hamstring flexibility or a history of hamstring injury.