I would love to hear the comments of more experienced runners on this graphic, which someone posted to my local parkrun page. I have no idea how authoritative it is and I realise many of us think in Centigrade and km rather than Farenheit and miles but is this in any way accurate? 80 to 85 Farenheit is 27 to 29 Celsius: for that, they say slow down by 2 mins per mile in low humidity or 5 mins per mile if it's humid. Those convert to 1'15" per km and 4'15" per km repectively, compared with temperatures below 55 Farenheit (13 Celsius). Experienced runners, is that over the top or realistic?
Slowing down in the heat - but how much? - Couch to 5K
Stats, correct or not... if it is this hot... slow right down and then some... ! Hydrate well.. every single day and do not push too hard!
Jeff Galloway says:
"You cannot run as fast when the temperature rises above 60F/14C. If you slow down 30 seconds a mile for every 5F increase above 60F, you can be the one who is finishing strong, passing other runners at the end. For every second you run too fast during the first half of a race on a hot day, expect to run 10 seconds slower at the end."
He also recommends NOT wearing a hat when it's hot, because most body heat is lost via the head.
In 2013, the authors of a scientific paper concluded, "This study demonstrates the importance of the head for evaporative heat loss"
Eur J Appl Physiol. 2013 Mar;113(3):735-41.
Quantification of head sweating during rest and exercise in the heat.
O'Brien C1, Cadarette BS.
I've not found any publications contradicting what you claim is a myth. Would be interested to see them if you have some citations to hand.
I loathe hats in any weather, and only grudgingly wear one if it is well below freezing.
It may be the lateness of the hour but as far as I can see the figures given in the abstract you cite do not suggest that more heat is lost from the head than from the equivalent unclothed body surface area anywhere else. It's just that other parts of the body are more likely to be clothed. Also the article is not about sports but about environments where protective clothing is needed: it's intended to inform the design of crash helmets and the like. As the Guardian article above puts it, if the myth were true going without a hat in cold weather would be as bad as going without trousers.
Unfortunately, I cannot find the actual research on which the people cited by the Guardian base their claims.
I certainly would not reach conclusions on the basis of a statement mediated by a newspaper reporter, be he from the Guardian, Express or Sun
Anecdotally, I am aware of a massive difference when I do or do not succumb to wearing a hat in very cold weather, so by reverse analogy I think having the head uncovered in very hot weather is equally beneficial.
Whether "most" or "some" heat is lost via the scalp, I'm happy to let it relieve me of as much heat overload as it can in current temperatures.
Not arguing with that, I'd rather not wear a hat either but in strong sun I have to or I'll get burnt. I just quibble with the assertion that 'most' heat is lost through the head. The figures in the article you cited actually suggest the opposite insofar as I can understand them. It says heat loss through the head is important but it does NOT say it is any more important than any other part of the body. The fact that I don't wear a hat is probably more than offset by the fact that I wear long joggers rather than shorts. It's also why wicking fabrics make a difference because they impede heat loss by evaporation much less than conventional fabrics.