Characteristics of Hamstring Electromyographic Activity and the Break-Point Angle during Nordic Hamstring Exercise at Different Ankle Positions

Nordic hamstring exercise (NHex) is well-known to reduce hamstring injury risk. However, the semitendinosus (ST) muscle is more activated than the biceps femoris long head (BFlh) muscle during NHex, though the BFlh muscle is more vulnerable to injury. It is important to investigate different NHex settings that may increase its effectiveness. This study aimed to examine the electromyographic (EMG) activity of the hamstring muscles and the break-point angle (BPA) during the NHex with the ankle joint positioned in plantar flexion (PF), dorsiflexion (DF) (neutral), and DF (neutral) with support. Twelve male volunteers without hamstring injuries in the four years preceding the experiment (age: 20.58 ± 0.9 years; body height: 171.1 ± 7.8 cm; body mass: 66.9 ± 12.2 kg) took part in the experiment. Participants randomly performed two sessions of the following exercise tests: NHex with ankle DF, NHex with ankle DF with sole support (DFS), and NHex with ankle PF. The EMG activity of the hamstring, BFlh, and ST muscles was measured for both the dominant and non-dominant limbs. The BPA was recorded using an IMU sensor. A repeated measures analysis of variance was conducted to assess hamstring muscle activity and the BPA. There was a significant main effect of EMG activity (p < 0.05) during the NHex under different ankle joint conditions for the BFlh in both the dominant and non-dominant legs. The findings indicated that EMG activity significantly increased during PF (p < 0.05) relative to DF and DFS for the BFlh in the dominant leg. Additionally, there were no significant differences in the BPA across different ankle positions (p > 0.05). This study demonstrated that the NHex elicited greater BFlh activity in PF than in DF and DFS.