Last week, our HUUB funded PhD student Philippa Jobling graduated from Nottingham Trent University. The final title of her thesis was 'Aerodynamic and thermoregulatory optimisation of tri-suit design for triathlon', which has shown fabrics perform optimally at different temperatures. It has little to do with how light or thin the fabric is and is governed by physics. HUUB prides itself on being the first to implement a multi-disciplinary approach to product innovation, where we have identified the critical importance of optimising the trade-off between aerodynamics and thermoregulation.
A triathlon consists of a swim, bike and run all completed in immediate succession. Events are either short (sprint) distance consisting of a 750m swim, 20km bike and a 5km run to long distance such as the world renowned Ironman races that consist of a 3.8km swim, a 180km bike and a 42.2km run. The rules and clothing differ across the varying distance disciplines. Due to the short, technical and draft legal nature of the sprint distance, very little consideration is given to materials in terms of their impact on athlete thermoregulation and aerodynamics even in warm weather as it will probably have little to no impact on performance, where it is common for competitors to wear sleeveless, all in one racing suits. However, when it comes to the longer distances, the non-draft legal rule means competitors gain no aerodynamic advantage from each other and have to rely on their own position and clothing design to make their cycling most efficient. For a half-ironman, triathletes usually wear all in one suits with rough fabrics incorporated into the long shoulder fabric that covers the arm down to the elbows, to aid aerodynamics. Over this long distance, triathletes push high power outputs for prolonged periods of time, resulting in concomitant high heat production. Therefore, it is important that the avenues of heat loss, either before or during the race, provide the athlete with sufficient cooling to prevent excessive heat strain and negative performance effects, especially when competing in high environmental temperatures. Performance benefits have been observed with multiple pre-cooling methods including ice-vests and cold water immersion, whilst many beneficial per-cooling methods are just too impractical to be adopted during a race. During the cycling phase, the largest avenue of heat loss is through convective cooling however, this may be inhibited by the aggressive aerodynamic positions adopted by triathletes. During this phase there becomes an important trade-off between improving aerodynamic efficiency whilst also maintaining sufficient heat loss. One way heat loss can be practically optimised is by smart fabric selection in the triathlon suits. By improving the movement of heat away from the body through increased conductivity, more efficient wicking and evaporation of sweat, could help maintain performance or allow triathletes to maintain a more aggressive aerodynamic position without such detriment to heat loss. Although it is difficult to select fabrics without first characterising them in terms of both their thermal and aerodynamic properties, which can be very costly, time-consuming and usually involves the use of a thermal manikin, hot plate methods or a wind tunnel. At present, little is know as to what extent the differences in fabric properties impact an athletes thermo-physiological response whilst cycling in environmentally stressful conditions where an optimised suit would be considered most beneficial.
Therefore, the aim of this research was to test the reliability of a new, faster method of measuring thermal conductivity and thermal effusivity of sports performance fabrics using a C-Therm device (Chapter 2), characterise performance fabrics currently used in elite sporting garments in terms of their thermal and aerodynamic properties (Chapter 3), understand how differences in thermal conductivity and thermal effusivity impact both thermo-physiology and thermal perception (Chapter 4), investigate whether the aerodynamic data collected is applicable in a field setting (Chapter 5) and finally to investigate how direct fabric manipulations designed to increase the efficiency of sweat evaporation impacts thermo-physiology and thermal perception when cycling in the heat (Chapter 6).
Several findings emerged including: 1) When using the C-Therm to measure the k and 𝜀 of a fabric intended to be worn as a single layer on the body, only 5 single layers of fabric are needed. Although the multi-layer vs single layer methods of testing fabrics cannot be used interchangeably, a linear regression can be used to derive results from one method to another. 2) Differences were observed in the thermal properties of the smooth fabrics and differences were identified in the aerodynamics properties of both smooth and rough fabric. This allowed for fabric selection for specific triathlon suits based on the cycling speed of the athlete for which it is intended to be used. 3) The magnitude of differences in thermal conductivity and effusivity measured were not enough to significantly impact thermo-physiology or thermal perception in an ambient temperature of 28°C and 65% relative humidity and in this instance aerodynamics should be prioritised. Individual differences should also be taken into account. 4) Differences in the main body fabrics of a triathlon suit can improve CdA without a change in position. Unless a significant thermoregulatory or perceptual benefit can be demonstrated in a fabric, the most aerodynamic fabric should be chosen over one optimised based on its thermal characteristics. 5) The findings of this thesis guides researchers and athletes as to how performance fabrics can be tested in the most valid, reliable and time efficient way possible whilst also providing an initial environmental threshold whereby the importance of aerodynamics outweighs the importance of thermoregulation.