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The idea of cyclists competing in 40-plus-degree heat might invoke images, for better or worse, of sweaty riders wearing fluorescent lycra.
But Tour Down Under (TDU) doctor Mark Fisher says it's the cyclists who aren't sweating that get his attention, because it's a sign of heat stress and a "confused body".
Dr Fisher has been on alert for the past two days as the TDU endures the best of Adelaide's summer weather — temperatures above 40C and a dry wind.
He follows the peloton in a tour car and, as well as being ready to act on accidents and injury, is on the lookout for the tell-tale signs of heat stress.
"It's usually a combination of starting to feel unwell, with headaches and a little bit of disorientation," Dr Fisher said.
"And often you sweat less because the body starts to get confused.
"You don't feel well. You don't feel right. And it's over and above the normal feeling of being hot and sweaty."
He said another sign, which could only be measured after the race, was weight loss.
In temperatures such as Friday's forecast 41C, cyclists can drink up to six litres of fluids during a race of up to four hours as they work to remain hydrated.
"If you lose weight from the beginning to the end of the race, invariably, that is fluid loss," Dr Fisher said.
"So that gives you a bit of an idea as to whether they are hydrated.
"For every kilogram of weight loss, that's at least a litre of fluid, so if they end up one or two kilograms lighter, that's a good sign they need urgent rehydration."
Thursday's stage of the race was shortened by 26 kilometres in response to the hot conditions, while Friday's 128km stage from Norwood to Uraidla was rescheduled to start one hour earlier to avoid the hottest part of the day.
The community challenge, in which enthusiasts pay to ride the same route as competitors, was cancelled by organisers, although it didn't stop hundreds of defiant riders from completing the route anyway.
Keeping core temperature down the key
Dr Fisher said the hydration of tour competitors was well-managed so they were "fed" plenty of fluids and electrolytes throughout the race from support cars.
"The concern often is their core temperature," he said.
"In hot conditions it can rise, and if they get too high they can start to suffer from significant heat stress.
"Fortunately, with all the changes in race conditions like shortening the race and allowing extra [fluid] feeding from cars, you can usually keep that under reasonable control, but you can never be absolutely certain that everyone's going to get through."
Dr Fisher has been the tour doctor for seven years and said he'd never had a cyclist come to him with issues during a race.
He did, however, need to respond to one cyclist who felt unwell at the hotel after Wednesday's stage two.
"You push the fluids. You make sure they are well fed with plenty of energy products so the body allows recovery. They all have massage and they often have cooling in the baths back at the hotel.
"The majority of them recover in a couple of hours. We've never had to send any of them off to hospital for emergency medical care.
"Really, they are well prepared for [the heat] and the majority seem to cope fairly well.
"But I wouldn't be recommending this sort of activity to an average cyclist who hasn't been conditioned or trained for it."
'Professionals will cope'
Brothers Wes and Ricky Swindale travelled from Queensland for the TDU in their sixth year watching the event.
Having competed at a lower level in the past, Wes said they arrived to "ride around watching the pro riders and to do a bit of cycling ourselves".
He said he believed the cyclists were "professionals who would cope" with the heat, and pointed out it was a dry heat and not humid.
"Sure, some of them will be a bit warm, and the British guys might find it a bit tough," he said.
"We saw them icing their helmets this morning before the start but I think they'll be alright."
"They're not going to go out there and forget to drink for three hours," Ricky added.
"They're going to be drinking every few minutes. They've got their directors who are going to be giving them water right throughout the race, so I think they'll be completely fine.
"It's a part of coming down here to Adelaide and you know what you're in for."
Topics: sport, cycling, human-interest, adelaide-5000, sa