Speed Matters in Nordic Hamstring Exercise: Higher Peak Knee Flexor Force during Fast Stretch-Shortening Variant Compared to Standard Slow Eccentric Execution in Elite Athletes.

Hamstring strain injuries are prevalent in many sports. Research has demonstrated that the Nordic hamstring exercise (NHE), a knee-dominant exercise addressing the posterior chain muscles, can aid in reducing the risk of hamstring injuries in athletes. However, most research on hamstring injury prevention has focused on performing the eccentric version of the NHE (NHE ECC ). In contrast, in sports, it is quite frequent for athletes to use an eccentric-concentric version of the NHE. Additionally, eccentric NHE is typically performed using a slow, controlled tempo. The effect of a fast stretch-shortening cycle NHE (NHE SSC ) compared to standard slow NHE ECC on peak knee flexor force has not been investigated. The aim of the study was therefore to investigate fast NHE SSC vs. standard slow NHE ECC . Our hypothesis posited that peak knee flexor force would be greater for fast NHE SSC compared with standard slow NHE ECC . The study involved 22 elite athletes (actively competing in both national and international events) consisting of female ( n = 10) and male ( n = 7) track and field athletes and male football players ( n = 5), aged 17-31 years. The participants performed maximum trials of slow NHE ECC and fast NHE SSC repetitions in which measurement of bilateral peak knee flexor force was conducted at the ankle with the use of a load cell. During the NHEs, a linear encoder was used to measure both the position where the peak knee flexor force was recorded and the average eccentric velocity. SSC contributed to an enhanced NHE performance, where bilateral absolute peak knee flexor force was 13% higher for fast NHE SSC vs. standard slow NHE ECC (822 vs. 726 N, p < 0.01, ES = 0.54). Participants achieved a 32% greater forward distance at the breakpoint stage during NHE ECC compared to the coupling phase for NHE SSC (54 vs. 41 cm, p < 0.001, ES = 1.37). Eccentric average velocity was more than three times higher for NHE SSC compared with NHE ECC (0.38 vs. 0.12 m/s, p < 0.001, ES = 3.25). The key findings of this study were that SSC contributed to an enhanced NHE performance, where absolute peak knee flexor force was 13% greater for fast NHE SSC compared to standard slow NHE ECC . The fast NHE SSC could therefore be an interesting alternative to the standard slow NHE ECC execution, as it may offer potential advantages for sprint performance, as well as hamstring injury prevention and rehabilitation.