We appreciate the opportunity to respond to the letter by Professor Walsh and colleagues,1 regarding our article, ‘Effects of partial sleep restriction and subsequent daytime napping on prolonged exertional heat strain’.2 They suggested that daytime napping following partial sleep restriction might increase the risk of exertional heat-related illness because the participants who took a nap felt ‘less hot’ and ‘less fatigued’ than if they had not taken a nap. In this context, they assume that an underestimation of physical and thermal strain during exercise in a hot environment results in …