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

Background 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 (BFLH) fascicle length and hamstring muscle size following 10-weeks of Nordic hamstring exercise (NHE) or hip extension (HE) training. Methods 30 recreationally active male athletes (age, 22.0 +/- 3.6 years; height, 180.4 +/- 7 cm; weight, 80.8 +/- 11.1 kg) were allocated to 1 of 3 groups: (1) HE training (n= 10), NHE training (n= 10), or no training (control, CON) (n= 10). BFLH fascicle length was assessed before, during (Week 5) and after the intervention with a two-dimensional ultrasound. Hamstring muscle size was determined before and after training via MRI. Results Compared with baseline, BFLH fascicles were lengthened in the NHE and HE groups at mid-training (d= 1.12-1.39, p < 0.001) and post-training (d= 1.77-2.17, p < 0.001) and these changes did not differ significantly between exercises (d= 0.49-0.80, p=0.279-0.976). BFLH 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 with the CON group, both exercises induced significant increases in semitendinosus volume (d=2.16-2.50, <= 0.002) and these increases were not significantly different (d= 0.69, p=0.239). Conclusion NHE and HE training both stimulate significant increases in BFLH fascicle length; however, HE training may be more effective for promoting hypertrophy in the BFLH.