Introduction
Participation in cold-water immersion (CWI) such as outdoor swimming and ice baths has increased in popularity over the last few years.1 These activities result in exposure to cold water in addition to the potential of low air temperatures and high winds when undertaken in seas, rivers or lakes. Due to this increase in participation, safety during immersion and the post-immersion period known as rewarming remains vital. The physiological responses to initial and prolonged CWI such as cold shock response and hypothermia are well documented.2 3 However, less research has been conducted on rewarming following CWI.
After CWI, a phenomenon known as afterdrop can occur, where there is a continued drop in deep body temperature during the rewarming phase.4 The afterdrop is thought to occur from cold blood returning to the core from the periphery of the body and is a serious complication of CWI and in extreme cases can lead to ventricular fibrillation. Current recommendations for rewarming include consuming a hot drink, relocating to a warmer environment and changing into warm/dry clothing.5 However, despite the potentially dangerous impact of CWI and the rising popularity of open water swimming and other water-based sports,1 6 little to no research has examined different types of clothing after CWI and the impact on physiological and perceptual responses.
A previous study has shown that woollen blankets were less efficient at preventing heat loss than foil blankets; however, this was an in vitro study and therefore making extrapolation of the findings to humans is difficult.7 Two previous studies have also investigated different clothing options to passively rewarm participants after placing them in wet clothing and concluded that the combination of an insulative layer with a vapour barrier is more effective at preventing heat loss and produces higher ratings of thermal comfort compared with single-layered options.8 9 This suggests the clothing worn after CWI to improve rewarming should be a combination of an insulative and vapour barrier layer. However, both of these abovementioned studies placed participants in wet clothing but did not immerse them in cold water.8 9 Therefore, to date, no study has yet specifically investigated the effect of different clothing options following CWI, in particular the comparison of single and dual-layered clothing.
A dryrobe is a commercially available garment that has been designed to support the rewarming phase following CWI.10 The dryrobe has a synthetic lambswool lining and a nylon waterproof outer shell.10 The garment was originally designed to improve on the existing option of a towel, and other alternatives such as the foil blanket which are used after races or during emergencies to rewarm humans. Theoretically, the dryrobe garment could provide a viable solution to improve rewarming post-CWI in humans; however, the efficacy of the garment in this situation has yet to be investigated.
Therefore, this study aimed to assess whether there were any differences in physiological (ie, deep body temperature, skin temperature or heart rate) or perceptual (ie, thermal sensation or thermal comfort) responses to wearing a dryrobe compared with a towel or foil blanket following 30 min passive CWI (14°C). It was hypothesised that the dryrobe would be the most effective option to improve physiological and perceptual variables during the rewarming phase.