Electromyographic activity of hip extensor muscles during Nordic hamstring and razor curl exercises on leveled and inclined shanks

Background Changes in electromyographic (EMG) activity of hip extensor muscles and knee flexion angles at peak biceps femoris long head (BFlh) EMG activity by different shank angles during razor curl (RC) exercises are unknown. Aims We investigated the changes in EMG activity of hip extensor muscles and knee flexion angle at peak BFlh EMG activity with different shank angles during RC and also compared the Nordic hamstring (NH) and RC exercises in the EMG activity of hip extensor muscles. Methods Twelve male university students randomly performed two repetitions of NH and RC with the lower leg slope angle set at 0° (NH0, RC0) and 40° (NH40, RC40). The EMG activity of hip extensor muscles was measured at the BFlh and related muscles. EMG activity was calculated based on the peak value of the root mean square, normalized as a percentage of the maximum voluntary isometric contraction. Results The BFlh EMG activity of NH0 was higher than that of RC0 ( p = 0.002) and RC40 ( p = 0.008). The knee flexion angle at peak BFlh EMG activity of NH0 was larger than that of NH40 ( p = 0.003) and RC40 ( p = 0.002), and RC0 was larger than that of NH40 ( p = 0.002) and RC40 ( p = 0.002). Conclusion NH40, the BFlh EMG activity equivalent to NH0, might be more effective for preventing recurrence of hamstring injury because the knee flexion angle at peak BFlh EMG activity remains within 30°, combined with a high BFlh EMG activity.