Author(s): YOU, Y., HIROSE, N., Institution: WASEDA UNIVERSITY, Country: JAPAN, Abstract-ID: 845

INTRODUCTION:
Eccentric hamstring exercises are widely used in injury prevention and performance training, and exercise- and region-specific differences in hamstring activation have been reported. However, how neuromuscular activation is continuously modulated across the joint range of motion, and whether such modulation differs between eccentric exercise tasks and muscle regions, remains poorly understood. Therefore, this study examined angle-dependent hamstring activation patterns during two eccentric exercises and assessed task- and region-specific modulation.
METHODS:
Twenty-five healthy, physically active males performed eccentric hip extension (HE) and incline Nordic hamstring exercise (INHE). Surface EMG was recorded from the biceps femoris long head and semitendinosus at proximal and distal regions during the eccentric phase, synchronized with joint angle data. EMG amplitude was normalized and analysed using linear mixed-effects models, with joint angle treated as a continuous predictor. Fixed effects included joint angle, exercise task, muscle region, and their interactions, with participant as a random effect.
RESULTS:
Across exercises and muscle regions, hamstring activation increased progressively with joint angle during the eccentric phase (β = 0.042 %MVIC·deg⁻¹, p < 0.001). However, significant task- and region-specific modulation was observed. A significant Angle × Task interaction indicated a steeper overall activation–angle relationship during INHE compared with HE (β = 0.011 %MVIC·deg⁻¹, p < 0.001). Importantly, this modulation differed by muscle region. During INHE, distal regions of both muscles demonstrated markedly steeper angle-dependent increases compared with proximal regions (e.g., distal biceps femoris: Δβ ≈ −0.115 %MVIC·deg⁻¹ relative to HE, p < 0.001), whereas regional differentiation was attenuated during HE. Significant three-way interactions (Angle × Task × Region, all p < 0.001) confirmed that exercise-specific neuromuscular control strategies emerged primarily at larger joint angles.
CONCLUSION:
Eccentric hamstring exercises are characterized by distinct, task-dependent and region-specific neuromuscular control strategies across the joint range of motion. The pronounced distal activation observed during INHE at increasing joint angles suggests exercise-specific demands on regional hamstring function, potentially reflecting greater lengthening requirements and joint torque demands as the movement approaches end range. These findings extend previous task- and region-based comparisons by demonstrating how hamstring activation patterns evolve dynamically across movement, providing a mechanistic link between exercise selection and joint-angle–specific loading. From a practical perspective, such angle-dependent regional modulation may be relevant for optimizing eccentric exercise selection and progression in injury prevention and performance-oriented training.