Gymnasiums were introduced in 900BC and Greek athletes practiced in the nude to the accompaniment of music. They also performed naked at the Olympic Games.
Why did the athletes compete in the nude?
The truth is that no one knows. According to one story, it began when a runner lost his loincloth and tripped on it. Everyone took off his loincloth after that. But ancient historians have traced it back to initiation rites—young men walking around naked and sort of entering manhood.
We know how fundamental nudity was to Greek culture. It really appealed to the exhibitionism and the vanity of the Greeks. Only barbarians were afraid to show their bodies. The nude athletes would parade like peacocks up and down the stadium. Poets would write in a shaky hand these wonderful odes to the bodies of the young men, their skin the color of fired clay.
But other cultures, like the Persians and the Egyptians, looked at these Greek men oiling one another down and writhing in the mud and found it very strange. They believed it promoted sexual degeneracy.