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

Strength transfer refers to the gain in strength in an untrained exercise resulting from training another exercise. This study aims to determine whether whole and selective hamstring hypertrophy influence the magnitude of strength transfer between the Nordic hamstring exercise (NHE) and the stiff-leg Deadlift (SDL). Using a blinded randomized controlled design, thirty-six resistance-untrained individuals were assigned either to a control group (CON), a NHE group, and a SDL group, the two resistance training programs being performed three times per week for nine weeks. Semimembranosus (SM), semitendinosus (ST), and biceps femoris (BF) hypertrophy was estimated from changes in the muscle volume. Strength transfer was measured by changes in the one-repetition maximum (1RM) of the non-trained exercise. After the resistance training programs, similar and significant whole hypertrophy was observed in both training groups (NHE: 11.4{+/-}6.5%, and SDL: 7.0{+/-}8.1%). The NHE group and SDL group, however, 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). Finally, non-significant correlations were found between strength transfer and both whole and selective hamstring hypertrophy (r[≤]0.3), except for the BF in SDL (r=0.6). We conclude that hamstring hypertrophy has a minimal role in strength transfer in resistance-untrained individuals. These findings suggest that, even in presence of hypertrophy, prevention and rehabilitation programs should include both Nordic hamstring and stiff-leg Deadlift exercises in the same training block to increase hamstring strength across both knee flexion-oriented and hip extension-oriented tasks.