Highly sensitive indicators of neck muscle fatigue derived from multimodal electrophysiological and metabolic coupling analysis

• Multimodal monitoring combining sEMG, NIRS, and 3D motion capture reveals dynamic coupling of muscle activation, metabolism, and motor control during neck fatigue. • Mean power frequency and muscle oxygen saturation decline significantly during sustained forward head posture, with metabolic changes preceding electrophysiological alterations. • The upper trapezius muscle fatigues earlier than the middle trapezius, indicating differential susceptibility to load. • Combined mean power frequency and muscle oxygen saturation metrics offer high sensitivity for early detection of neck muscle fatigue.