Knee Flexor Activation during Nordic Curl Hamstrings Exercise with Varying Load Assistance

Purpose: The Nordic curl hamstrings exercise (NHE) is a widely adopted training technique used to reduce hamstring injury occurrence.NHE can be difficult to perform and often results in substantial fatigue and exercise-induced muscle damage.To reduce this burden, NHE can be performed with counterweight assistance to reduce mechanical and neuromuscular load.The aim of this pilot study was to compare muscle activation -measured via surface electromyography (sEMG) -during NHE repetitions performed with 25% and 50% of bodyweight assistance.Methods: Twelve healthy adults with experience performing NHE performed three sets of three NHE repetitions, either unloaded or with assisting counterweight (25% or 50% of bodyweight) using a plate-loaded Nordic curl bench.Average sEMG amplitude was captured from biceps femoris throughout the eccentric phase of each NHE repetition.Results: Muscle activation was reduced with 25% assistance compared to unloaded condition (p < 0.001 [95% CI: -7.95,-2.17]),and with 50% assistance compared to 25% assistance (p < 0.001 [95% CI: -15.79,-10.06])and to unloaded condition (p < 0.001 [95% CI: -20.87,-15.09]). Conclusion:Knee flexor muscle activation during the eccentric phase of NHE repetitions demonstrated a dose-dependent decrease as counterweight assistance was increased to 25% and to 50% of bodyweight.These preliminary findings can support sport and exercise practitioners seeking to reduce the mechanical and neuromuscular load associated with NHE and inform future research investigating the assisted NHE.