Many cultures swear by the benefits of a hot bath. But only recently has science began to understand how passive heating (as opposed to getting hot and sweaty from exercise) improves health. At Loughborough University we investigated the effect of a hot bath on blood sugar control (an important measure of metabolic fitness) and on energy expended (number of calories burned). We recruited 14 men to take part in the study. They were assigned to an hour-long soak in a hot bath (40˚C) or an hour of cycling.