India, Jan. 17 -- Every step a race-walker takes is calculated, down to the finer twists of the joints. Which is why Rhydian Cowley was taken aback when it all fell apart.

He was midway through a 35-km race at the 2023 World Athletic Championships, in Budapest. He had been worried about the temperature and humidity. (The race started at 22 degrees Celsius and 81% humidity and finished at 28 degrees Celsius C and 60% humidity, in harsh, direct sun, he says).

Suddenly, he found himself on the ground. He tried to hoist himself up using the side rails, but he could barely stand. He had suffered a heat stroke.

"It is scarier to reflect on the moment now," he says, "because you realise how vulnerable you were."

To the 34-year-old Australian...