Effects of Dose Response of Nordic Hamstring Exercise on Muscle Strength, Agility and Speed in Athletes

One of the most common injury in sports is the Hamstring injury, as hamstring is very susceptible to tears and strains. Hamstring muscle strain-type injuries are common in sports that involve high degree of speed, power and agility such as sprinters, soccer, basketball, tennis and football. Occurring in both recreational and professional sports, these injuries can result in substantial time lost from sport and commonly recur.

When sprinting, the hamstring muscles of the swing leg function concentrically as hip extensors to quickly swing the thigh back, whereas the same muscle group acts eccentrically as knee flexors to decelerate the forward swing leg. This last action is a probable contributing injury mechanism because of the increased peak hamstring musculotendinous stretch, activation, and active lengthening contraction of the hamstring muscles. The Nordic Hamstring Exercise (NHE) was previously termed the 'Russian hamstring exercise'. This is a partner exercise which can be performed easily on the pitch without special equipment. The NHE involves the player attempting to resist a forward-falling motion from a kneeling position, eccentrically contracting hamstring muscles and thought to replicate hamstring function during terminal swing phase. NHE is a preventive strategy which may reduce the incidence of hamstring injury, medical costs, and personal suffering of the injured player keeping in view the training exposure, training intensity, and compliance to preventive measures. Programs that include the NHE reduce hamstring injuries by up to 51%. The NHE essentially halves the rate of hamstring injuries across multiple sports in different athletes. Even in the face of promising NHE preventive effect shown by previous studies,adoption and implementation of the NHE programs is still low. Evidence show improvement in performance, agility and speed in athletes by NHE training but lowest dose of NHE required to enhance athletes' performance , agility and speed is yet to be found. This study attempts to investigate the lowest dose response of NHE by comparing the effects of high volumes of NHE with low volumes of NHE.

Literature review: Mjølsnes et al first demonstrated that a NHE program performed on the training environment of professional soccer players is more effective in developing maximal eccentric hamstring strength than a comparable program based on hamstring curl machine at the fitness center.

Three large prospective trials (two randomized and one non-randomized) reduced injuries by approximately 70% by implementing the NHE in a team's training regime. The results from the meta-analysis suggested that teams using the NHE (in isolation or as part of a larger injury prevention program) reduced hamstring injury rates up to 51%.

Brooks et al studied the effects of the NHE on the incidence and severity of hamstring strains among 546 professional rugby union players. The NH exercise group had a significantly lower hamstring injury rate and severity than the strengthening and the stretching/ strengthening group.