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Hamstring strain injuries (HSIs) remain a burden with high prevalence rates. The Nordic Hamstring exercise (NHE) has been found to be effective in preventing HSIs. However, the preventive mechanisms are not fully understood. Changes in stiffness are postulated as a possible protective mechanism. Surprisingly, the effect of the NHE on the stiffness of different hamstring muscles has never been investigated before. Therefore, the aim of this Randomised controlled trial was to investigate the impact of a 10-week NHE programme on the eccentric strength and the shear wave velocity (proxy of stiffness) of the hamstrings. Thirty-six soccer players were randomly assigned to either the control or the experimental group. The experimental protocol consisted of the incorporation of a 10-week NHE programme within the normal training routine. The hamstring stiffness and eccentric strength were assessed before and after. Within-group analyses showed a significant increase in strength, only for the experimental group. However, no significant effect of the NHE was found on the stiffness of each hamstring muscle. A 10-week NHE programme does not affect hamstring stiffness, despite an increase in eccentric strength, indicating that the preventive mechanism of the NHE is probably not (co-)explained by alterations in hamstring muscle stiffness.
Pieters et al. (Fri,) studied this question.