Doha - Women's marathon runners were rushed for medical attention, faces contorted in pain while other competitors hobbled off the track in the inaugural road race of Doha's World Athletics Championships.
Humidity of more than 73 percent and temperatures of almost 33 degrees Celsius (91 degrees Fahrenheit) dogged the race, specially started at midnight to avoid peak heat, as it meandered along a course on Doha's Corniche coast road.
"You see somebody down on the course and it's just, extremely grounding and scary," said Canada's Lyndsay Tessier, 41, who was one of those to finish, coming in ninth. "That could be you in the next kilometre, the next 500 metres."
"It was just really scary and intimidating and daunting. So that was enough to hold me back."
Around two dozen runners in the 68-strong marathon field fell by the wayside as the sweltering conditions took their toll, in a sport which rarely sees drop outs at this level.
Kenya's Ruth Chepngetich won gold when she took the tape after 2 hours 32 minutes and 43 seconds, crediting "training in a hot area" of her home country for helping her to tame the elements.
Tessier's fellow competitors filed behind her as she spoke to the media, some held up by their coaches and others too exhausted to stop and speak.
"I'm just really grateful to have finished standing up," added Tessier.
The Championships' organisers told race participants that the event's timing could be changed if conditions proved prohibitive but ultimately pressed ahead with the original plan.
Almost all of the runners were saturated with sweat by the halfway point and most ran with bottles as some video cameras being used to film the race malfunctioned because of the conditions.
A mild breeze that lapped the corniche during the opening ceremony and fireworks display had dwindled by the end of the race leaving the runners to bear the brunt of the surging humidity.- 'Guinea pigs' -
Marathon runners and walkers do not have the luxury of competing in the championships' principal venue, the air-conditioned Khalifa Stadium where the climate is maintained at 23-25 degrees.
France's defending 50 km walk world champion Yohann Diniz strongly criticised the IAAF for being made to compete in Doha's humid conditions.
"I am extremely upset. If we were in the stadium we would have normal conditions, between 24-25 degrees, but outside they have placed us in a furnace, which is just not possible," he said on Friday.
"They are making us guinea pigs."
Tessier said that seeing so many competitors drop out of one race was "alarming and you feel for them because you do know the training that's gone into this".
"You know how badly everyone wants it and wants to be here. You don't wanna finish it or end it that way," she said as sweat dripped off her face and a team member followed behind her with water.
Throughout the race, medical golf carts ferried runners who dropped out to a busy medical tent as a team of doctors, which included an expert on heat in sports, assessed their condition.
Namibia's Helalia Johannes, who secured bronze, said hydration also played a key role in her strong showing.
"I cannot say I enjoyed the event - there was a song that says 'I must finish'," she said.
"I didn't miss any water point."