Citius
Guest
I had a quick search, and BC seem to admit that it's anecdotal and "traditional". Certainly not science based advice: "If you adhere to traditional cycling thinking, you should not expose your knees in temperatures below 15˚C." Linky
I doubt if there is any actual 'science' behind any of it - if there was, Russian pensioners would not be jumping through holes in the ice, wearing just a pair of trunks in order to go swimming in the Volga on new year's day.
Nevertheless, BC academy advice remains pretty consistent.