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 to 1.39, p < 0.001) and post-training (d = 1.77 to 2.17, p < 0.001) and these changes did not differ significantly between exercises (d = 0.49 to 0.80, p = 0.279 to 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 to 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.
Reproduced with permission from the BMJ Publishing Group.

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