Effects of Unilateral Nordic Hamstring Training with a Sloped Platform on Biceps Femoris Fascicle Length in Athletes with a History of Hamstring Strain Injury

Research has yet to investigate the effects of unilateral Nordic hamstring training with a sloped platform (UNHT) on the fascicle length of the biceps femoris long head (BFlh FL) in previously injured legs. This study aimed to address this gap. A longitudinal pre–post design without a control group was used to examine the effects of 6 weeks of UNHT in eight young male athletes with a history of hamstring strain injury (HSI). Pre- and post-training measurements of middle and distal BFlh FL in the injured and uninjured legs were obtained using ultrasonography. At baseline, middle BFlh FL was significantly shorter in the injured leg than in the uninjured leg (86.0 ± 9.0 mm vs. 99.9 ± 7.6 mm, p < 0.001). Following UNHT, middle BFlh FL significantly increased in both the injured (105.8 ± 9.4 mm, p = 0.001) and uninjured legs (108.0 ± 10.3 mm, p = 0.596). Distal BFlh FL significantly increased in the injured leg (72.4 ± 7.1 mm to 85.7 ± 8.0 mm, p = 0.012), whereas the uninjured leg showed a smaller, non-significant change (72.8 ± 5.5 mm to 79.1 ± 7.5 mm, p = 0.069). These findings demonstrate that UNHT increased BFlh FL in previously injured legs. Because shorter BFlh FL and reduced eccentric strength are established risk factors for HSI, these adaptations may have implications for risk reduction; however, recurrence prevention was not assessed in this study.