Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: Implications for injury prevention

The architectural and morphological adaptations of the hamstrings in response to training with different exercises have not been explored. PURPOSE - To evaluate changes in biceps femoris long head (BF LH ) fascicle length and hamstring muscle size following 10-weeks of Nordic hamstring exercise (NHE) or hip extension (HE) training. METHODS - Thirty recreationally active male athletes (age, 22.0 ± 3.6 years, height, 180.4 ± 7 cm, weight, 80.8 ± 11.1 kg) were allocated to one of three groups: 1) HE training (n=10), NHE training (n=10), or no training (CON) (n=10). BF LH fascicle length was assessed before, during (Week 5) and after the intervention with 2D-ultrasound. Hamstring muscle size was determined before and after training via magnetic resonance imaging. RESULTS - Compared to baseline, BF LH fascicles were lengthened in the NHE and HE groups at mid- (d = 1.12 – 1.39, p 0.05). BF LH volume increased more for the HE than the NHE (d = 1.03, p = 0.037) and CON (d = 2.24, p < 0.001) groups. Compared to the CON group, both exercises induced significant increases in semitendinosus volume (d = 2.16 – 2.50, ≤ 0.002), however, only the HE group displayed increased semimembranosus volume (d= 1.57, p = 0.007). CONCLUSION - NHE and HE training both stimulate significant increases in BF LH fascicle length, however, HE training may be more effective for promoting hypertrophy in the BF LH and semimembranosus than the NHE.