Abstract
Hamstring strain injuries (HSIs) remain a prevalent and costly concern in professional rugby union, often linked to short biceps femoris long head (BF_LH) fascicles and poor eccentric knee flexor strength. This study evaluated the efficacy of a modified Nordic Hamstring Exercise (mNHE) protocol—incorporating a progressive hip flexion angle—on BF_LH architectural adaptations and eccentric strength. Thirty professional rugby union players were randomized into either an mNHE training group (n = 15) or a traditional NHE control group (n = 15) for an 8-week intervention during the pre-season. BF_LH fascicle length was assessed via B-mode ultrasonography, and eccentric knee flexor strength was measured using a NordBord dynamometer at baseline and post-intervention. The mNHE group demonstrated a significantly greater increase in BF_LH fascicle length compared to the control group (14.2% vs. 5.1%, p < 0.01) and a superior improvement in peak eccentric torque (18.6% vs. 8.4%, p < 0.01). These findings suggest that introducing hip flexion during the NHE enhances architectural remodeling by promoting sarcomerogenesis and greater eccentric strength gains. Incorporating the mNHE into rugby conditioning programs may offer superior protection against HSIs by targeting key modifiable risk factors more effectively than the traditional protocol.
