Quantifying the Physiological and Biophysical Time-Course of Human Heat Adaptation

The present thesis builds on existing work done in the field of human thermoregulation, with a specific focus on the impact of repeated heat exposures to a natural (acclimatisation) or artificial (acclimation) environment on physiological adaptation and heat stress risk. The aim of the experimental study presented in chapter 3 was to model the independent influence of different environmental and personal parameters on predicted acclimatisation status throughout a representative year in Australia. Chapter 4 aimed to quantify the time course of changes in ωmax throughout 7 consecutive days of heat acclimation. Finally, chapter 5 aimed to develop a novel, non-invasive method to assess changes in physiological heat acclimation status in an at-home setting

Sweat

Over the last years continuous and non-invasive measurement techniques to gain insight in health and performance have become popular. These continuous and non-invasive biochemical measurement techniques are commonly manifested in wearable sensors for which sweat is the most preferred bodily fluid to use due to its easy and continuous accessibility and rich biomarker content. Currently sweat sensor developments are largely technology driven while the scientific foundations for the monitoring of health and performance via sweat often are lacking. In the current thesis we aimed to contribute to knowledge on how sweat composition is affected and how to measure sweat in a reliable way. Direct relations between blood and sweat are often assumed. For many components in blood it has already been established how their concentrations relate to specific diseases or sports performance. We have shown that during submaximal exercise relations between blood and sweat sodium, chloride, potassium, lactate, ammonia and glucose were non-significant. Therefore, it may be more relevant to establish what information is in sweat itself and how it varies within individuals. Subsequently, we observed that sweat becomes less salty during heat acclimation. In this way, sweat composition could provide information about the physical state of the body (in this case heat acclimation). By obtaining such knowledge, we hope that athletes and/or healthcare could be eventually be provided with meaningful feedback about physiological parameters based on sweat

Oral application of L-menthol in the heat: From pleasure to performance

When menthol is applied to the oral cavity it presents with a familiar refreshing sensation and cooling mint flavour. This may be deemed hedonic in some individuals, but may cause irritation in others. This variation in response is likely dependent upon trigeminal sensitivity toward cold stimuli, suggesting a need for a menthol solution that can be easily personalised. Menthol’s characteristics can also be enhanced by matching colour to qualitative outcomes; a factor which can easily be manipulated by practitioners working in athletic or occupational settings to potentially enhance intervention efficacy. This presentation will outline the efficacy of oral menthol application for improving time trial performance to date, either via swilling or via co-ingestion with other cooling strategies, with an emphasis upon how menthol can be applied in ecologically valid scenarios. Situations in which performance is not expected to be enhanced will also be discussed. An updated model by which menthol may prove hedonic, satiate thirst and affect ventilation will also be presented, with the potential performance implications of these findings discussed and modelled. Qualitative reflections from athletes that have implemented menthol mouth swilling in competition, training and maximal exercise will also be included