Context: Different resistance exercise determinants modulate the musculotendinous adaptations following eccentric hamstring training. The Nordic Hamstring Exercise (NHE) can be performed 2-fold: the movement velocity irreversibly increases toward the end of the range of motion or it is kept constant.
Design: This cross-sectional study aimed to investigate if the downward acceleration angle (DWAangle) can be used as a classification parameter to distinguish between increasing and constant velocity NHE execution. Furthermore, the kinetic and kinematic differences of these 2 NHE execution conditions were examined by analyzing the DWAangle in relation to the angle of peak moment.
Methods: A total of 613 unassisted NHE repetitions of 12 trained male sprinters (22 y, 181 cm, 76 kg) were analyzed.
Results: The majority of analyzed parameters demonstrated large effects. NHEs with constant velocity (n = 285) revealed significantly higher impulses (P < .001; d = 2.34; + 61%) and fractional time under tension (P < .001; d = 1.29; +143%). Although the generated peak moments were significantly higher for constant velocity (P = .003; d = 0.29; +4%), they emerged at similar knee flexion angles (P = .167; d = 0.28) and revealed on average just low relationships to the DWAangle (Rmean2=22.4%). DWAangle highly correlated with the impulse (Rmean2=60.8%) and δ (DWAangle-angle of peak moment; Rmean2=83.6%).
Conclusions: Relating DWAangle to angle of peak moment assists to distinguish between significantly different NHE execution, which will potentially elicit different musculotendinous adaptations. These insights are essential for coaches and athletes to understand how to manipulate eccentric hamstring training to change its purpose.
Keywords: eccentric resistance training; hamstring strength; kinematic analysis; movement velocity; time under tension.