Minimal Role of Hamstring Hypertrophy in Strength Transfer Between Nordic Hamstring and Stiff-Leg Deadlift: A Blinded Randomized Controlled Trial.

Morin, T, Doguet, V, Nordez, A, Caillet, A, and Lacourpaille, L. Minimal role of hamstring hypertrophy in strength transfer between nordic hamstring and stiff-leg deadlift: a blinded randomized controlled trial. J Strength Cond Res XX(X): 000-000, 2025-Strength transfer refers to the gain in strength in a nontrained exercise resulting from training another exercise. This study aims to determine whether whole and selective hamstring hypertrophy influences the magnitude of strength transfer between the Nordic hamstring exercise (NHE) and the stiff-leg deadlift (SDL). Using a blinded randomized controlled design, 36 resistance-untrained individuals were assigned to a control group (CON), an NHE group, or an SDL group. The 2 resistance training programs were performed 3 times per week for 9 weeks. Semimembranosus (SM), semitendinosus (ST), and biceps femoris (BF) hypertrophy was estimated from changes in the muscle volume using 3D ultrasound. Strength transfer was measured by changes in the 1RM of the nontrained exercise. After the resistance training programs, similar and significant whole hamstring hypertrophy was observed in both training groups (NHE: 11.4 ± 6.5%, and SDL: 7.0 ± 8.1%). The NHE group and SDL group presented a selective hypertrophy of ST (24.3 ± 10.8%) and SM (11.2 ± 12.7%), respectively. Conversely, no difference in strength transfer was observed between the NHE group (10.7 ± 8.5%) and the SDL group (20.7 ± 15.0%) (p = 0.06; 95% CI 0.3-20.4%, d = 0.87). Finally, nonsignificant correlations were found between strength transfer and both whole and selective hamstring hypertrophy (r ≤ 0.45), except for the BF in SDL (r = 0.60). We conclude that hamstring hypertrophy has a minimal role in strength transfer in resistance-untrained individuals. These findings suggest that, even with hypertrophy, coaches and practitioners should include both Nordic hamstring and stiff-leg deadlift exercises in the same training program to enhance hamstring strength in knee flexion and hip extension tasks, benefiting both performance and injury prevention.