Publications

Background: This study aimed to examine the immediate effects of the Nordic Hamstring Exercise (NHE) on the stiffness of the biceps femoris (BF) and semitendinosus (ST) muscles.

Methods: This parallel-group randomised controlled trial followed CONSORT 2025 guidelines. Twenty-four physically active adults (16 females, 8 males) were randomly assigned to an NHE group (n = 12) or a control group (n = 12) using 1:1 gender-stratified randomisation. The NHE group performed 3 sets of 10 repetitions of the NHE, while the control group remained inactive. Muscle stiffness of the BF and ST was assessed pre- and post-intervention using the MyotonPRO device.

Results: No significant overall changes in hamstring stiffness were observed within or between groups (p > 0.05). Within the NHE group, the ST tended to increase in stiffness (11.25 N/m, p = 0.057), while the BF showed a small, non-significant reduction (−12.00 N/m, p = 0.696). The difference in changes between BF and ST was significant (p = 0.039). Independent of group allocation, males demonstrated significantly higher baseline stiffness than females for BF (258.13 vs. 195.81 N/m, p < 0.001) and for ST (247.88 vs. 174.00 N/m, p = 0.003). Regression analysis showed that only height predicted the change in ST stiffness after NHE (R = 0.625, R2 = 0.39, p = 0.030).

Conclusions: A single NHE session did not alter overall hamstring stiffness but produced opposite, muscle-specific effects. More research with larger, uniform samples is needed to confirm these findings.

Keywords: injury prevention, lower limb, posterior thigh, sports injuries

This randomised controlled trial tentatively indicates that a single session of the NHE may produce distinct immediate mechanical responses across hamstring muscles rather than a uniform change in stiffness. Although overall hamstring stiffness did not significantly change immediately after exercise, the semitendinosus tended to increase in stiffness, while the biceps femoris appeared to become more compliant. Although these differences were modest, they reached statistical significance when comparing changes within groups, suggesting that eccentric loading through the NHE might shift mechanical stress towards the medial hamstring, likely because of its dominant activation during the movement. Nevertheless, these findings warrant cautious interpretation. The observed trends may merely indicate transient viscoelastic modifications of superficial tissues rather than authentic intramuscular mechanical remodelling, considering that stiffness was assessed using the MyotonPRO device, which predominantly detects superficial and tone-related characteristics. Furthermore, the limited sample size, mixed-gender sample, and brief measurement period constrain the broader applicability of these results.

Collectively, the findings do not endorse the notion of an immediate, uniform stiffening of the hamstrings following NHE; rather, they indicate a complex, muscle-specific mechanical response. This may contribute to a reduced risk of lateral hamstring strain injuries, particularly considering the vulnerability of the biceps femoris long head. Nonetheless, in the absence of long-term follow-up or concurrent electromyographic and elastographic validation, definitive causal inferences remain unwarranted. Future investigations involving larger, more homogeneous cohorts and employing multimodal stiffness evaluation methods (such as the integration of MyotonPRO, SWE, and EMG) are essential to ascertain whether the observed differential stiffness responses are transient mechanical phenomena, early indicators of muscle adaptation, or measurement artefacts.