Heat And Moisture Transfer In Knitted Fabrics And Its Influences On Human Physiological Health During Exercise

Clothing offers as an active media between the human body with tightly thermoregulated core temperature and the surrounding environment. Heat exchange between human body and the environment depends on the status of human body and the ambient climate conditions (temperature, relative humidity and wind), but also modified by the physical properties of clothing in different level. As clothing is an layer between surrounding environment and human body, which form a microclimate between human body and surrounding environment. "It is important to realize that the clothing is not just a passive cover for the skin, but that it interacts with and modifies the heat regulating function of the skin and has effects which are modified by body movement."The heat and moisture transfer of textile materials is a very complex procedure. The heat transfer and moisture transfer and distribution interact and vary with the condition (temperature, humidity, heat and moisture transfer process) changes, modified by the physical properties of the textile materials. With the advance of textile technology, in order to meet and even exceed consumers' needs and expectation, functional textile materials have been developed to use in sportswear, where comfort, movement, and performance are emphasized.Human body is an open, adaptive organic system with great flexibility. The heat production and releasing, heat stress, cardiovascular responses and nervous system responses of the human body are highly related during exercise. During which, increased muscular activity causes an increase in heat production in the body, due to inefficiency of the metabolic reactions, which must be dissipated to prevent a deleterious increase in body temperature. The most effective means which man posses for equalizing heat production and heat loss under hot conditions is sweating to create a latent heat flux by the evaporation of sweat at the skin. The heat and moisture transfer properties of clothing is decisive at a certain extent in whether the increased inner heat and liquid sweat of the human body can be successfully transferred to the clothing outside and dissipate to reduce human heat stress as well as enhance comfort sensation, especially under hot environment.In the present research project, different knitted fabrics, featuring in different liquid water transfer and distribution properties, were designed and produced by selecting and matching fiber of different hygroscopicity, and yarn of different surface energy as well as moisture management design in a double-surface knitting structure.Wear trial was carried out to investigated the different influences of the clothing made of the fabrics mention above respectively by measuring and recording the microclimate temperature and humidity, mean skin temperature, ear canal temperature, heart rater, blood pressure, heart rate variability, and urine catecholamine of the wearer as well as collecting the wearers' subjective perception of heat, moisture, comfort and tiredness. The systemic comparison and analysis together with detailed discussion and interpretation was developed based on these results in terms of influences of fiber hygroscopicity, yarn surface energy and fabric moisture management respectively.Via factorial analysis and linear correlation analysis, the relationship between fabric heat and moisture transfer properties and human body physiological responses, and wearer's subjective thermal, moisture and comfort perceptions were revealed.Comparing with previous research in related area, the set point and research methodology of the present study is different and novel. It is the first time that the different controlling of liquid water transfer and distribution within fabrics in three dimensions was systematically realized by fiber, yarn and fabric structure selecting and matching; the influences of fabric heat and moisture on human physiological responses during exercise and recovery in hot and dry environment condition was firstly investigated; the relationships between fabric liquid water transfer properties and human physiological responses as well as subjective sensations were firstly revealed. The main findings are as follows:(1) The influences of fiber hygroscopicity on human physiological responses vary under different liquid water transfer and distribution (LWTD) circumstance: under hydrophilic circumstance, cotton clothing was better than polyester clothing to reduce heat stress but caused higher cardiovascular drift, lower physiological stress, stronger thermal, moist, discomfort and tiredness sensations because cotton fiber has higher hygroscopicity with much great extent to absorb moisture vapor and liquid sweat; under hydrophobic circumstance, the heat is mainly released by evaporation at clothing outer surface and polyester clothing is better than cotton clothing in terms of moisture permeability, which caused the wearers in lower heat stress, higher cardiovascular drift, lower stress, weaker thermal perception; under moisture management circumstance, polyester clothing caused lower heat stress, cardiovascular drift, lower stress and weaker thermal perception; under reversed moisture management circumstance, cotton fabric caused higher thermal stress, cardiovascular drift and strong thermal and moist perception.(2) The surface energy of fabric had different influences on cotton fabrics and polyester fabrics. For cotton fabrics, hydrophilic cotton clothing has advantage than hydrophobic to reduce heat stress, but caused stronger cardiovascular drift, lower physiological stress, and stronger thermal and moist sensation, weaker tiredness sensation. For polyester fabrics, hydrophilic polyester fabric caused lower heat stress, and tended to caused stronger cardiovascular drift and stronger thermal perception and weaker moist perception.(3) The moisture management capacity of fabric had different influences on cotton fabrics and polyester fabrics too. For cotton fabrics, moisture management (MM) cotton clothing has advantage than reversed moisture management (RMM) cotton clothing to reduce heat stress, but caused stronger cardiovascular drift, lower physiological stress, and stronger tiredness sensation in the end of trial. For polyester fabrics, moisture management had no significantly different influences on thermophysiologcial responses but caused stronger cardiovascular drift and stronger moist perception in the trial end.The results systematically and clearly show that the different liquid water transfer and distribution properties of the clothing, due to different fiber hygroscopicity, yarn surface energy and fabric moisture management capacity matching of the fabrics, caused different changes in human-clothing microclimate in different extent, which further affected the heat and moisture balance between the human body and the surrounding environment as well as the cardiovascular responses and subjective sensations in different level. All these results and findings are of great significance for sportswear design and choosing subject to different wearing condition and exercise intensity in order to decrease heat stress as well as increase performance. And they are also valuable for fabric, textile materials, and clothing designing targeted for sports consume market.