Hamstring muscle strains are common injuries in sports that require maximum sprinting, kicking, acceleration, and change of direction. A significant amount of time is lost from competition and training (18 days on average) after a hamstring strain injury which can be devastating for athletes and sport teams.
A major problem with hamstring strains is that coaches and athletes must deal with the frustration of persistent symptoms and a high percentage (12–31%) of reinjuries. In contact team sports, especially those that involve kicking, the anatomy of the hamstring muscle places it in a vulnerable position.
The hamstring muscle is a bi-articulate muscle, meaning it crosses two joints and has two major actions, hip extension and knee flexion. This also means that the hamstrings are stretched with hip flexion and knee extension. As the lower leg swings forward during the late swing phase of running, the hip flexes and the knee extends simultaneously. Thus, the hamstring muscle becomes actively lengthened to greater than normal lengths.
Simultaneous hip flexion and knee extension also occur when kicking a ball placed on the ground or in the air. Kicking while running or running on an incline puts the hamstrings in an even more vulnerable position because of a forward trunk lean.
According to numerous recent studies, almost two-thirds of hamstring injuries might be prevented by increasing eccentric strength of the hamstring (muscle lengthening). One of the more popularized modalities of eccentric strengthening is the Nordic hamstring exercise. The exercise in some cases has seen athletes reduce their risk of hamstring strains by 51%.
The below graphic demonstrates the protocol for the Nordic hamstring exercise:
1. After ensuring your muscle tissue temperature is high, kneel on the ground with a spotter securing your ankles from behind.
2. Then, lean forward so that your chest begins to approach the ground.
3. Utilize your hamstrings to resist gravity, ensuring you move as slowly and smoothly as possible.
4. Put your arms out to break your final fall, allowing your chest to gently touch the ground, before pushing yourself upright to repeat the exercise.
It should be noted that significant fatigue can be induced after only one set of five repetitions of this exercise. Therefore, be cautious of prescribing any sets and repetitions prior to training. Instead, consider prescribing the exercise after training, as it may reduce potential risks for inducing hamstring strains during training.
Holistic hamstring health should involve not just the Nordic hamstring exercise. Instead, strength, running and flexibility training modalities are all important components of any comprehensive hamstring strain injury prevention programmes.
Thelen, D, Chumanov, D, and Hoerth, M. Hamstring muscle kinematics during treadmill sprinting. Med Sci Sports Exerc38: 108–114, 2005.