Improvement of thermal perceptions and physiological responses using torso heating under short-term cold exposure

Short-term cold exposure (<1 h) may adversely affect human thermal comfort and health. Few studies have investigated the effectiveness of body heating in providing thermal protection to the torso against sharp temperature decreases, as well as the optimal operation modes of torso heating equipment. In this study, 12 male subjects were acclimatised in a room at 20 °C, then exposed to a cold environment at -2.2 °C, and finally returned to the room for recovery; each phase lasted 30 min. During cold exposure, they wore uniform clothing with an electrically heated vest (EHV) operated under these modes: no heating (NH), stage-regulated heating (SH), and intermittent alternating heating (IAH). Variations in subjective perceptions, physiological responses, and temperatures set for heating were recorded during the experiments. Torso heating mitigated the adverse effects of the large temperature down-step and continuous cold exposure on thermal perception and decreased the occurrence of three symptoms: cold hands or feet, running or stuffy noses, and shivering during cold exposure. After torso heating, the same skin temperature of the non-directly heated parts corresponded to a higher local thermal sensation, which was attributed to an indirect effect of the improved overall thermal state. The IAH mode could achieve thermal comfort at a reduced energy level, and it outperformed SH in subjective perception enhancement and self-reported symptom relief at lower heating temperatures. Additionally, under the same heating setting temperatures and power capacity, it could achieve an approximately 50 % longer usage time than SH could. The results suggest that intermittent heating protocol can be an efficient way to achieve thermal comfort and energy savings for personal heating devices.