Hamstrings muscle dynamics during the Nordic hamstring exercise and high-speed running.

The Nordic hamstring exercise (NHE) and high-speed running are widely used training modalities to prevent hamstring strain injuries, yet the differences in the muscle lengths, forces, power, work, and impulse between these training modalities remain unclear. Thus, in this study, we compared model-estimated dynamics of the most frequently injured hamstrings muscle, biceps femoris long head (BFLH), for 14 participants (8 male and 6 female) performing the NHE and running between 4 and 8 m/s. We collected motion capture data to drive musculoskeletal simulations to estimate muscle fiber lengths and velocities, and muscle-tendon unit force, power, work, and impulse during the NHE and running. We found that peak estimated muscle-tendon unit forces were greater during high-speed running (≥ 7.5 m/s) than the NHE (p < 0.05), and that high-speed running (≥ 6 m/s) also featured higher muscle fiber lengths and lengthening velocities (p < 0.05). Estimated negative muscle-tendon unit work was significantly greater during the NHE compared to running at all speeds (p < 0.001) because of the greater change in muscle fiber lengths during the NHE (p < 0.001). In contrast, estimated peak negative muscle-tendon unit power was significantly lower during the NHE compared to running at 5 m/s and above (p < 0.01). In addition, estimated muscle-tendon unit impulse was significantly greater during the NHE compared to running at all speeds (p < 0.001). Our simulations revealed marked differences in the biomechanical demands of the NHE and running on the BFLH.