Neuromuscular Responses to Unilateral and Bilateral Execution of Eccentric Exercises: A Multidimensional sEMG Study

Hamstring injuries are frequent in sports, often linked to eccentric overloading during sprinting. While eccentric strengthening, like Nordic curls and hip extensions, is common, the impact of exercise symmetry (unilateral vs. bilateral) on neuromuscular control remains unclear. This study aimed to investigate regional/task-specific neuromuscular strategies during unilateral and bilateral eccentric loading of the same exercises. Twenty-five healthy and physically active young men (age: 24.52 ± 3.82 years; height: 175.53 ± 5.44 cm; weight: 72.06 ± 7.44 kg) were recruited based on physical activity screening, with the exclusion criteria including recent lower limb injuries. Participants performed unilateral and bilateral curls and extensions with surface electromyography on hamstrings, gluteus maximus, and trunk stabilisers. Parameters like root mean square and median frequency were extracted and statistically compared. Unilateral execution generally elicited higher muscle activation, particularly in middle hamstring regions (30.65% to 38.38% in RMS, r = -0.84 to -0.77, p_FDR < 0.001). Frequency differences revealed region-specific neuromuscular strategies. Intra-hamstring comparisons revealed significantly higher median frequencies in the BF50 and ST30 regions at their respective anatomical locations (dz = -1.90 to 1.34, all p_FDR < 0.001). These findings suggest that exercise symmetry and anatomical specialisation jointly shape neuromuscular control, with implications for designing eccentric training to reduce injury risk.