Eccentric Hamstring Torque Production and Muscle Activity in Unassisted Versus Assisted Nordic Hamstring Exercises

The aim of this study was to compare hamstrings eccentric torque production and muscle activities during one maximal repetition of conventional unassisted (CNHE) and assisted (ANHE) Nordic Hamstring Exercise. Twelve participants randomly performed 5 different NHE variations at maximal intensity. We calculated maximal hamstring eccentric torque production (Tmax), torque time integral, root mean square at Tmax, and electromyography integral for 7 muscles during exercises. CNHE resulted in lower Tmax and torque time integral (P < .05) compared with ANHEs. Moreover, it exhibited lower electromyography integral for the biceps femoris, semitendinous, gastrocnemius lateralis, and gastrocnemius medialis (P < .05). Unilateral ANHE simulating the late-swing phase of the step cycle (ANHELSU) demonstrated greater Tmax compared with bilateral and unilateral ANHE (P < .01), whereas root mean square at Tmax was lower during ANHELSU than bilateral ANHE (P < .05). The increased eccentric torque production and higher muscle activities during ANHE could be attributed to greater muscle length at the end of the movements and a longer time under tension. Our results suggest that (1) ANHE increases hamstrings torque production and muscle activities of the knee flexors compared with CNHE, and (2) ANHELSU is the only variation specific to the injury kinematics that maximizes overall eccentric torque production.