Burrows, AP, Cleather, D, Mahaffey, R, and Cimadoro, G. Kinetic and electromyographic responses to traditional and assisted Nordic hamstring exercise. J Strength Cond Res 34(10): 2715-2724, 2020-The Nordic hamstring exercise (NHE) is performed to increase hamstring strength, elicit morphological changes, and reduce injury risk. However, to date, the NHE assisted by the means of an external resistance has not been investigated. Thus, this study compared the eccentric knee flexor strength, rating of perceived exertion (RPE), and electromyographic responses of the biceps femoris (BF) and semitendinosus (ST) when performing the NHE under assisted or unassisted conditions. Sixteen professional soccer players (aged 19.4 ± 2.2 years) performed 5 sets of 3 NHE unassisted and with assisting loads (5-20% of the body mass) using the Keiser machine. Eccentric knee flexor strength was measured from the subjects' dominant limb. Peak surface electromyography (sEMG) of the BF and ST was recorded from the dominant limb; the ratio was also calculated. Subjects rated the intensity of each condition of the NHE on a ten-point RPE Borg scale. All assisted conditions displayed significantly lower (p < 0.05) absolute and relative eccentric knee flexor strength than unassisted conditions. Rating of perceived exertion for each loading condition was significantly lower (p < 0.05) as the assisting load increased except for the difference between the 10 and 15% assisted conditions. Surface electromyography of the BF and ST was not significantly lower (p < 0.05) during all assisted conditions compared with the unassisted NHE, neither there were significant between-muscle differences or sEMG ratios. Our findings suggest that the assisted NHE reduces the load and difficulty of the exercise. Practitioners can use the assisted NHE to manipulate intensity and difficulty if that is appropriate for their programming.