Tagami K (2025) Perspectives on Heatstroke Avoidance with Textiles and Fashions. Ann Sports Med Res 12(1): 1234.

Heatstroke must have existed before humans were aware of it. It is not difficult to imagine that humans have caused many casualties of this disease in Africa and beyond. They acquired clothing as a countermeasure, but now we are facing a crisis of what is called “climate change and global warming”. When we reached the space or the moon, we had to avoid the powerful heat source of solar radiation. This difficulty was handled by air conditioning inside the cabin of the spacecraft and space suit, so the role of the clothing and fashion world was limited on that occasion. How humans take against this new crisis of weather change? Countries and regions around the world have established their own guidelines for the heatstroke prevention and been trying to deal with it mainly from the perspective of treating patients. The act of finding patients, treating them, and returning them to life is important and worthy of respect. However, the almost citizens would like to see concrete measures to prevent their onset of the disease. In other words, we probably want the unknown cause of the disease to be identified so that they can eliminate it with their own hands.

The etiology of heatstroke has simply been explained as “heat accumulation”. Heat sources are heat generated inside the body, and environmental heat sources (radiant heat sources and high temperatures, etc.) flown into. The flow of heat in and out of the body is called heat exchange or balance, and the rate of heat exchange is called the amount of heat exchange. In heat exchange, there is a custom of using different terms depending on the direction of heat flow, with heat leaving the body being called “heat release or outflow” and heat entering the body being called “heat input or inflow”. There are four routes of heat exchange: conduction, convection, radiation, and evaporation, but in an active body, conductive heat exchange is often ignored because the contact area with solid materials is small. The only part of the body where heat exchange occurs is the respiratory organs, where heat is released directly from the body to the outside air, but all other dissipation occurs on the skin surface. Heat exchange on the skin surface is determined their direction and amount of flow by the gradient of temperature or water vapor partial pressure between skin surface and ambient air. The amount of heat exchange for each of the four routes follows different physical principles, so it is calculated using a different formula. The sum of these is the amount of heat exchange for an individual.

When measuring the amount of heat exchange (W/ m2) of the human body in the laboratory, it has been calculated by dividing the product of the change in body temperature (°C), specific heat and his or her mass (kg), which are indicators of state, by the body surface area [1]. Measurements of human subjects are often restricted from the perspective of research ethics, and thermal manikins have come to be used frequently [2]. Furthermore, today, heat flow meters are commercially available, and the amount of heat exchange has become a directly readable indicator. The author assembled a Surface Heat Exchange Measuring Device (SHED) in which a heat flow meter is attached to a Peltier element and adjusted to a temperature equivalent to skin temperature [3], and standardized it [4]. For example, the authors observed Exertional Heat Stroke (EHS) that occurred during running in cold weather and clarified through desk experiments why runners get overheated in the midwinter [3]. In this case, they interpreted that the runner, who produces 10 times more heat than at rest, is simultaneously facing two difficulties: difficulty in dissipating heat and the inflow of solar radiant heat. They concluded that the force causing this is a drop in skin temperature. In fact, the skin temperature measured by a marathon runner running in winter was below 20°C [5].

The calculation formulas for heat exchange by conduction, convection, and radiation are complex, but the elements and coefficients are simple and easy to understand. On the other hand, the calculation formula for evaporative heat exchange is complex and difficult with many elements. In particular, it is difficult to understand and feel the saturated water vapor pressure, which changes greatly depending on the temperature, and this cannot be explained by relative humidity (%). In addition, the relationship between heat stress and meteorological observations in runners during winter races was examined, and it was shown that they experienced a decrease in running speed accompanied by heat stress [6]. The cause of heat stress in runners running at a speed of 20 km/h is also a drop in skin temperature, and it is thought to be due to the inability to ensure a water vapor pressure difference between the outside air and the skin surface.

More than 30 years have passed since major global sporting events were moved from autumn to mid-summer, but no country has taken effective measures to prevent their heatstroke of athletes. The organizing committee for the event plans to hold the event in the early morning or late evening. However, these plans cannot be a definitive solution because lower temperatures can be lowered vaper saturation and it promote difficulty of sweat evaporation. The heatstroke experienced by runners in mid-summer can be explained also by deducing the results of runners in midwinter. In other words, the only one cause of heatstroke experienced by runners during the day in mid-summer is the inability to raise the skin temperature to a temperature at which heat can be dissipated. It is said that the core body temperature of runners rises to around 40°C while running [7,8], but there is little knowledge about the skin temperature of runners during a race in midsummer [9]. A runner generates 10 times more heat than his/her resting. He/She must dissipate all of this heat, but the lowered skin temperature by cold ambient temperature avoids sweat evaporative and convective heat dissipation. If the skin temperature can be maintained even 1°C higher than the ambient temperature, it is possible to avoid heat retention in runners. In other words, as long as the temperature is not abnormally high, exceeding the runner’s core body temperature during their races, marathon races in midsummer are safe. Athletes from countries that have heat retention countermeasure technology that induces a higher skin temperature will have an advantage in the race. The possible technology will be existed in Textile and Fashion world.

What is the process that causes classic heat stroke, which occurs when the body’s metabolic heat production level is low? The process that leads to heat accumulation in classic heat stroke is no different from that in exertional heat stroke. If heat production has fallen to the level of basal metabolism, it is reasonable to assume that heat flows into the body from the air by convection and to use the structural materials of the house as a radiant heat source. It is important to suspect the presence of factors/ substances that lower the skin temperature of people with normal metabolic function in a high- temperature environment. Skin temperature rises by circulating high-temperature blood deep inside the body to the skin surface. At that time, the diameter of the capillaries in the skin is expanded to reduce blood circulation resistance. All factors/substances related to this work to suppress heat retention, while factors/substances with the opposite effect work to promote heat retention. In addition, the disappearance and excretion of each factor/substance from the body have the exact opposite effect. There should be many specific factors/substances, and we would like you to consider natural and artificial substances contained in foods, luxury items, medicines, cosmetics, daily necessities, etc. as candidates.

As explained so far, the only cause of heatstroke and heat retention, regardless of whether they are exertional or classical, is a decrease in the amount of heat released from the skin surface. Textiles and fashion are industries that have historically committed to skin heat dissipation, and should continue to lead the way in ensuring the safety of citizens and preventing heatstroke. A decrease in heat dissipation is caused by a decrease in skin temperature, so textile and clothing design can take advantage of fibers, fabrics, designs, and usage methods that do not lower skin temperature to prevent heatstroke. Outdoor work clothes for midsummer already cover the entire body, but we would like to entrust the realization of work clothes that apply the unprecedented concept of “increasing skin temperature to increase heat dissipation” to fabric and clothing engineers. Another important issue is reducing the solar radiation heat load on sunny days. Generally, fabrics block 50% of solar radiation heat. Increasing this to 70-80% will be a blessing for those who work outdoors or play sports. The solar radiation heat load around Tokyo is about 200W/m2, and the ground radiation heat in midsummer has an energy intensity comparable to this. In other words, when working on the ground on a sunny summer day, where both types of radiant heat are radiated, the radiant heat equivalent to the heat generated by the runner is applied. The contribution of heat shielding to the prevention of heat stroke is greater than one might imagine. If a fabric can shield 80% of the heat, it will reduce the radiant heat load from 400 W/m2 to 80 W/ m2, regardless of the temperature. The caps or hats are clothing that block the solar radiant heat from reaching the scalp. However, their structure has the disadvantage of avoiding heat dissipation from the scalp and increasing heat accumulation. The running cap has a structure that promotes heat dissipation from the scalp through convection and evaporation by taking in air and sending it out along the scalp. If a fabric with high heat shielding performance (80% or more) can be supplied for caps or hats, the technology can be called complete. We hope that such caps or hats will be supported by users at high risk of heat stroke.

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