Characteristics of facial electromyography during cold exposure and feasibility of evaluating thermal comfort

A comfortable building environment plays a vital role in enhancing both the physical and mental well-being of its occupants. In recent years, the assessment of building thermal environments has gained significant attention. The assessment methodology is shifting from subjective evaluations to more physiological assessments. However, the exploration of facial muscles in this context has remained largely uncharted territory. The primary objective of this research was to investigate the characteristics of facial electromyography (fEMG) in a cold environment and examine its potential for assessing thermal comfort. The experiment was divided into two parts. The first part focused on understanding fEMG characteristics in the time domain, frequency domain, and phase during activities like speaking, expressing emotions, and exposure to cold conditions. The second part aimed to study the recovery process of fEMG after cold exposure, achieved by increasing clothing insulation and raising air temperature. The findings revealed significant distinctions in fEMG characteristics when subjects engaged in speaking (notably in the low-frequency component of the anguli oris muscle), expressing emotions (with a prominent low-frequency component in the zygomatic muscle), or experiencing cold conditions (highlighted by the high-frequency component of the masseter muscle). Interestingly, augmenting clothing insulation in the body region posed challenges in improving facial muscle electrical activity, while raising air temperature effectively alleviated facial muscle tension. This study represents the pioneering application of fEMG in indoor thermal comfort evaluation. It offers a physiological foundation for assessing thermal comfort based on facial skin temperature and facial expressions. Furthermore, the research contributes valuable data that can support the advancement of wearable devices and smart building systems.