The Assessment of Practical Per-Cooling Targeting Peripheral Limbs During Exercise in Hot and Humid Environments

When excess body heat generation owing to the performance of exercise coincides with the heat dissipation limitations presented by hot and humid environments, the body’s ability to maintain thermal balance is compromised, and internal temperatures can rise to dangerous levels. Individuals who exercise in hot environments commonly look to acute cooling strategies to provide thermoregulatory assistance in order to avoid the health risks and performance decrements brought about by elevated thermal stress. Many cooling techniques aim to apply cold surfaces to large areas of skin on the torso, head, or neck to extract heat directly from core regions of the body. These locations, however, are often difficult to access without disrupting movement. In many exercise modalities including cycling, paddle sports, or wheelchair sports, however, peripheral regions such as the upper or lower limbs remain almost stationary, and may present a convenient location to apply cooling garments/equipment without disrupting required movements. The research studying the impact of practically applicable cooling techniques at these locations, however, is limited and inconclusive, prompting the present work. This document first outlines the quantifiable heat transfer principles that determine human thermal behaviour, and discusses the effects of thermal stress and acute cooling interventions. It then outlines practical considerations regarding the applications of cooling techniques, motivating the proposal of a novel technique that does not interfere with exercise performance by targeting the volar forearm skin of cyclists during exercise. The impacts of forearm cooling are then assessed experimentally during cycling ergometry exercise in a hot and humid environment. The cooling was observed to reduce the rate of core temperature rise by 0.43 ± 0.34°C/hr (p=0.002), while also eliciting significant reductions in heart rate drift and rating of thermal comfort. Computational modelling of the human thermal system was then employed to extend the experimental investigation and assess what impact the cooling may have during true cycling applications outside of the laboratory setting. Model outcomes suggest that the effects of the outdoor environment may reduce the effectiveness of the applied cooling slightly, but that the cooling will still be capable of providing quantifiable benefits. The impact of the cooling was also simulated across a range of ambient conditions, and the cooling was generally observed to be more impactful in hotter air temperatures and at higher ambient humidity levels