Neuromuscular activation patterns of the hamstrings and trunk during eccentric exercise in athletes and physically active adults

BACKGROUND: Eccentric hamstring exercises are widely used in training and rehabilitation settings, yet how neuromuscular activation patterns vary with training status remains unclear. We aimed to compare hamstring and trunk neuromuscular activation patterns elicited by two commonly used eccentric hamstring exercises-the Inclined Nordic Hamstring Exercise (INHE) and Bilateral Hip Extension (BHE)-between trained athletes and physically active nonathletes. METHODS: Twenty-five healthy male participants (10 athletes and 15 physically active nonathletes) performed INHE and BHE in randomized order. Surface electromyography (sEMG) was recorded from hamstring and trunk musculature during the eccentric phase. Root mean square (RMS, normalized to %MVIC), median frequency (MF), and the biceps femoris long head to semitendinosus (BFlh/ST) activation ratio were analysed. Between-group differences were assessed using non-parametric statistics with effect size estimation. RESULTS: Athletes exhibited higher RMS values in the BFlh during BHE and a tendency toward BFlh-dominant activation (BFlh/ST ratios > 1), although between-group differences in the ratio were not statistically significant. Physically active nonathletes exhibited significantly higher MF values in several muscles and showed comparatively greater activation of trunk musculature under specific task conditions. They also demonstrated a comparatively greater reliance on the semitendinosus, with lower BFlh activation amplitudes and lower BFlh/ST ratios, as well as comparatively higher activation of superficial trunk muscles under specific task conditions. CONCLUSIONS: Distinct neuromuscular activation patterns during eccentric hamstring exercises were observed between athletes and physically active nonathletes, despite comparable overall activity levels. These findings should be interpreted as associative and descriptive and suggest that training status may be associated with differences in task-specific hamstring and trunk coordination strategies during eccentric loading.