Objectives To evaluate how separate and combined climatic parameters affect peak core temperature during exercise in the heat using computer simulations fed with individual data. Methods The impact of eight environmental conditions on rectal temperature (T re) was determined for exercise under heat stress using the Fiala-thermal-Physiology-and-Comfort simulation model. Variations in ambient temperature (T a ±6°C), relative humidity (RH±15%) and solar radiation (SR+921 W/m 2) were assessed in isolation and combination (worst-case/best-case scenarios) and compared with baseline (T a 32°C, RH 75%, SR 0 W/m 2). The simulation model was fed with personal, anthropometric and individual exercise characteristics. Results 54 athletes exercised for 46±10 min at baseline conditions and achieved a peak core temperature of 38.9±0.5°C. Simulations at a higher T a (38°C) and SR (921 W/m 2) resulted in a higher peak T re compared with baseline (+0.6±0.3°C and +0.5±0.2°C, respectively), whereas a higher RH (90%) hardly affected peak T re (+0.1±0.1°C). A lower T a (26°C) and RH (60%) reduced peak T re by-0.4±0.2°C and a minor-0.1±0.1°C, respectively. The worst-case simulation yielded a 1.5±0.4°C higher T re than baseline and 2.0±0.7°C higher than the best-case condition. Conclusion Combined unfavourable climatic conditions produce a greater increase in peak core temperature than the sum of its parts in elite athletes exercising in the heat.

Eleven phase change materials (PCMs) for cooling humans in heat-stressed conditions were evaluated for their cooling characteristics. Effects of packaging material and segmentation were also investigated. Sample packs with a different type PCM (water- and oil-based PCMs, cooling gels, inorganic salts) or different packaging (aluminum, TPU, TPU + neoprene) were investigated on a hotplate. Cooling capacity, duration, and power were determined. Secondly, a PCM pack with hexagon compartments was compared to an unsegmented version with similar content. Cooling power decreased whereas cooling duration increased with increasing melting temperature. The water-based PCMs showed a >2x higher cooling power than other PCMs, but were relatively short-lived. The flexible gels and salts did not demonstrate a phase change plateau in cooling power, compromising their cooling potential. Using a TPU or aluminum packaging was indifferent. Adding neoprene considerably extended cooling duration, while decreasing power. Segmentation has practical benefits, but substantially lowered contact area and therefore cooling power.

The 2020 Olympics will take place in Tokyo. The expected heat and humidity will cause severe heat stress for athletes. To improve safety and performance of Dutch athletes during the Olympics the project “Thermo Tokyo – Beat the Heat” was started. This is a multidisciplinary project in which multiple universities, companies, sports organizations and sport innovator centers take part. Sailors are prone to heat issues because they are obliged to wear an insulating flotation aid. And they are not sheltered from the sun. The Sailing Innovation Center came with the proposition to design a cooling garment for Dutch sailors that are competing in the 2020 Olympics. The sailing context was analyzed. The best option for sailors is a cooling vest that can be applied underneath the flotation aid. Sailing regulations forbid wearing a cooling vest during a race because of the added weight around the torso. A cooling vest can still be worn before and in between races. According to literature, pre-cooling can have a possitive effect on exercise performance in hot and humid conditions. Using a Phase Change Material (PCM) is the best cooling technique for the sailing context. PCMs do not requires special equipment, only a freezer for recharging and a coolbox for transport are needed. Also, the cooling power of a PCM is independent from the environment. Project partner Inuteq provided PCMs for the project. Multiple PCMs were analyzed. A paraffin based PCM with a phase change temperature of 6,5°C is best for short and intense cooling. Combining ice with a thin layer of Neoprene is the best option if cooling duration is important. Laser sealing TPU sheets made it possible to create custom shaped cooling packs quick and easy. Multiple forms were tried. A raster of hexagons showed the right balance between flexibility and rigidity. Seven iterations of ideating, designing, prototyping and testing were executed. This lead to the design of a cooling vest that is easy to use at sea. It can be applied quickly underneath sailing clothing. And it can be stored in a medium sized coolbox. The design as proposed can not be produced on short notice by partner Inuteq. With some compromise the most imporant features of the design were transfered to a design that is producible well before the Olympics. The cooling power and duration of the vests is estimated by combining results from lab and exercise tests. The method used to make this estimation does not require a thermal mannequin. And it can be used for a variety of cooling vests. The vest is compared to other vests previously evaluated in literature. It is almost certain that the vest will have a positive impact on exercise performance in hot and humid conditions. It is hard to compare sailing to the exercise protocols used to measure the effect of cooling garments on sport performance. Nevertheless, it is likely that sailors can benefit from using a cooling vest during the 2020 Olympics if weather conditions are as expected.