Exploring the relationship between muscle activity, jaw behaviour and pain.

While muscle overload is commonly implicated in musculoskeletal pain conditions, real-time assessment of associated behavioural and physiological features is challenging. This study aims to investigate the relationship between self-reported awake bruxism using Ecological Momentary Assessment (EMA) and jaw muscle activity registered by surface electromyography (sEMG), and differences between individuals with and without temporomandibular disorder (TMD) pain. Seventy participants (38 women, 32 men), of which 31% reported pain, completed 3-day EMA using a smartphone application combined with a sEMG device only for day 1. Overload, defined as muscle activity exceeding 20% of maximum voluntary contraction (MVC), was evaluated for duration and area under curve (AUC). A strong correlation was observed between EMA-reported bruxism and sEMG overload duration (ρ = 0.62, p < 0.001). AUC showed a correlation with EMA only in the TMD group. Participants with TMD pain exhibited shorter high-intensity bursts (60-79% MVC, p ≤ 0.005) but prolonged low-intensity muscle activity (20-39% MVC, p < 0.001). Bruxism behaviour and stress levels were higher in women and in individuals with pain. The results suggest that combining EMA and sEMG provides valid assessment of musculoskeletal overload, capturing both perceptual and physiological dimensions. Incorporating EMA in pain management can identify pain-related risk behaviours, thus supporting tailored patient-centred interventions.