There's the pressure of competition, but at Tokyo 2020 the athletes are also having to contend with another challenge -- intense heat and humidity.
"Temperatures have spiked today (Saturday) to near 34°C (93°F) across the greater Tokyo region," according to CNN's weather team.
"This combined with oppressive humidity levels above 80% puts a strain on the human body as it exerts itself in outdoor competition. When humidity levels are high, your body can't properly cool itself and over-heating can easily occur."
Richard Carapaz won Ecuador's first gold medal of the Tokyo Games in the 234-kilometer men's cycling road race in brutally hot conditions.
Meanwhile, Russian tennis star Daniil Medvedev cooled himself down with a mobile air conditioner during his Tokyo 2020 tennis match at the Ariake Tennis Park.
After he beat Kazakhstan's Alexander Bublik 6-4 7-6 in the men's singles first round, Medvedev described the conditions as "some of the worst (heat) I've ever had."
On Friday, Olympic Russian Archer Svetlana Gomboeva Gomboeva fainted during the Olympic archery qualification tournament, Russian state news agency TASS reported.
"With Sveta everything is normal. She was seen by doctors, they gave ger to drink water. They said it was a normal sunstroke, she needs to go home and sleep," the Russia Olympic said in a statement Friday.
"She has already been released, now we all together are returning to the Olympic Village. Sveta is with us, she is feeling well. So she will be part of the competing team," the statement added.