Author(s): FROUIN, A., LE SANT, G., BARBIER, L., JACQUEMIN, E., MCNAIR, P., ELLIS, R., NORDEZ, A., LACOURPAILLE, L., Institution: NANTES UNIVERSITY , Country: FRANCE, Abstract-ID: 1177

INTRODUCTION:
The hamstring muscles play an important role in many sports, and hamstring muscle strengthening is needed to improve performance and prevent injuries (1). Hamstring strengthening programs are commonly composed of hip extension-oriented (e.g., stiff-leg deadlift) and/or knee flexion-oriented (e.g., leg curl) exercises. It is well known that a similar magnitude of muscle hypertrophy can be achieved across a wide spectrum of loading ranges from 30% to 80% of 1-RM. In recent years, low load training has been combined with blood flow restriction (BFR) to promote muscle hypertrophy (2) and enhance strength (3). However, the effect of such loading combined with blood flow restriction on the distribution of hypertrophy within the hamstring muscle group has not been investigated.
METHODS:
A parallel randomized controlled trial design was implemented to compare the effect of a nine-week of High Load (HL) or Low Load-Blood flow restriction (LL-BFR) resistance training on the distribution of hamstring muscle hypertrophy. Participants were randomly allocated to one of three groups: HL, LL-BFR and control (CON). Two training sessions were composed of (a) stiff-leg deadlift and front squat and (b) a bi-set of bilateral seated leg curl and seated leg extension. They were alternated over the duration of the training program. Muscle volumes were assessed the week before and after the training program with freehand 3D ultrasound (3DUS) measurements (4).
RESULTS:
Notable hypertrophy was observed for the ST (+26.5%) and SM (+17.1%) (all P values <0.01) during HL, while no changes were found for BF (+4.0%; P=1.0). LL-BFR group exhibited significant hypertrophy for SM (+21.6%), BF (+14.6%) and ST (+12.2%) (all P values <0.01).
CONCLUSION:
Although LL-BFR and HL improved hamstring muscle volume to a similar extent, its distribution differed between SM, ST and BF. The hypertrophy was most in ST and SM for the HL group while it was balanced across all muscles for the BFR-LL group, the magnitude of which varied greatly among participants. These results provide new findings for optimizing training, prevention, and rehabilitation programs that aim to induce a selective hypertrophy among the hamstring muscles.

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3. Lixandrão ME, Ugrinowitsch C, Berton R, et al. Sports Med. 2018;48(2):361–78.
4. Frouin A, Guenanten H, Le Sant G, et al. Ultrasound in medecine and Biology. 2023;49(6):1457–64.