There are few works paying attention to the simulation of thermo-physiological responses of people exercising in the cold, where the bioheat status and exposure environments are much different from the scenes focused by previous models. For example, the body heat production by activities with middle or high intensity and heat-moisture transfer through multi-layer clothing. Also, basal metabolic rate and basal blood flow is found be affected by the difference of tissue temperature and its setpoint, and this temperature difference may be significant for those exposed to the cold environment for a long time. Clothing is a significant factor that affects human thermo-physiological responses by influencing heat and moisture exchange between the body and environment, especially in cold weather and with body's regulatory sweating. Various thermo-physiological models have taken into account the effects of clothing, a number of which simplify it by two parameters, thermal insulation and evaporative resistance. Given the complicated process of heat and moisture transfer through skin, air gap, clothing layers and environment, such a simplification can hardly explain the exact mechanism of the influence of clothing on human thermo-physiological responses. Some researchers have given further and microscopic insight in modelling the heat and moisture transfer in clothing by considering the processes of heat conduction, radiation, convection, moisture evaporation, diffusion, condensation and sorption. But these works are solely clothing models and cannot be directly utilized to calculate human thermo-physiological responses. However, most of these models only consider single layer clothing system or simplify the multi-layer clothing system as one layer. For those who exercise in cold environments, they usually wear multi-layer clothes with much different fabric properties of each layer. A simplified one-layer clothing model is not accurate enough to describe both the heat-moisture transfer process and the factors that may influence this process (e.g. the air gap between the adjacent layers). Wan and Wang proposed a multi-layer clothing model but their model was particularly applicable for clothing with PCM material and cooling fans used in normal or high temperature environments. Joshi et al. specifically studied the effect of air gap by considering its spatial heterogeneity, and then Joshi et al. developed a multi-layer clothing model considering the spatially heterogenous air gap coupled with a 3D thermoregulation model. But moisture sorption and pumping effect were neglected in their work, which is significant in the clothing of exercising people. Related research is still lacking for people exercising in cold, whose bodies sensible and latent heat dissipation are both significant and thus required to be properly modeled. In addition, a thermo-physiological model needs to be validated by human subject tests data. A number of models mentioned above are validated by experimental data in normal temperature conditions, while some researchers have conducted human subject experiments in cold environments to study thermo-physiological responses and provide model validation data. For example, Nielsen and Nielsen reported a test under a cool environment to explore the distribution of subjects' skin temperature and thermal sensation. Gavhed and Holmer conducted experiments in various cold environments to collect human thermo-physiological data to validate the Duration Limited Exposure Index. Male's thermo-physiological responses under extremely cold environments were studied by Wu et al. to test human responses in extreme weather conditions. However, the subjects in these experiments are all asked to keep rest or walk slowly dressed in cold protective clothing. Chen et al. conducted experiments to study the thermo-physiological responses of subjects exercising in various ambient temperature conditions. But local skin temperatures were not reported and air velocity, an important factor that affects people participating in cold weather activities, was not considered. In general, the experimental studies and dataset are still limited for thermo-physiological responses of subjects exercising in cold environment wearing specific activity suits. To address the prediction of thermo-physiological responses including skin and core temperatures of people exercising in cold environments, a multi-node thermo-physiological model based on Takahashi et al. work is presented in this paper, integrated with a proposed multi-layer clothing model and corrections considering exposure characteristics. The concept of net exercise efficiency is used to calculate the metabolic heat production during middle or high intensity exercise. The low temperature effects on the metabolic rate and blood flow are taken into consideration. The clothing model particularly considers the air gaps between the clothing layers to reflect the ventilation and air penetration effect affected by ambient wind.

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Regards,
Catherine
Journal Co-Ordinator
Annals of Biological Sciences