A biomechanical monitoring framework for supine sleep: continuous muscle state assessment using sEMG-JASA synchronized with interface pressure mapping

Sleep quality is fundamentally linked to health, and prolonged static postures during sleep can induce muscular fatigue, discomfort, and musculoskeletal risk. A critical gap exists in understanding the continuous relationship between muscle state dynamics and body-mattress interface pressure throughout sleep, which is essential for developing ergonomically adaptive sleep systems. Ten healthy adults maintained a supine posture on a standardized mattress equipped with a high-resolution pressure array. Surface electromyography was recorded from the trapezius, erector spinae, gluteus medius, and biceps femoris muscles. Muscle states were classified using the joint analysis of EMG spectrum and amplitude (JASA) method across three hours of sleep. Regional pressure parameters were calculated for the shoulder, waist & back, hips, and thigh. Muscle states exhibited distinct regional and temporal patterns: trapezius activity remained stable (recovery/force decrease), erector spinae progressively shifted toward fatigue, gluteus medius transitioned from fatigue toward recovery, and biceps femoris showed increasing fatigue. Interface pressure was highest at the shoulder and hips. Statistically significant negative correlations were identified between muscle fatigue and regional pressure, most strongly between gluteus medius fatigue and hips pressure distribution (Kendall's<i>τ</i>= -0.723,<i>p</i>< 0.01). Reduced interface pressure in partially suspended body regions appears to elicit compensatory muscle activation, leading to fatigue accumulation. The JASA method effectively discriminates muscle states during prolonged supine posture, providing a biomechanical basis for real-time, pressure-modulating interventions aimed at improving sleep recovery and comfort.