The Ancient Greek nude is in fact a complicated and mysterious thing. Although, first thing to know is that they simply haven't consider the nudity in the way we do. Briefly nudity represented a complex ‘costume’ and a cultural
ideal, suitable for heroes, warriors, and gods as well as athletes. Thus, heroic nudity served not only as a mean of creating role models, but also as an expression of a worldview that unite the ethical and the aesthetic qualities of objects and phenomena. Beautiful and worthy should have been not only one's own body and soul, but also the challenges, achievements and sources of pride. Nudity for a Roman was inappropriate in everyday life and was considered natural only for barbarians and slaves. On the other hand nudity was quite acceptable practice in ancient Greek society. In 520 B.C. the armed race was introduced at Olympia which can partly be explained as a reminiscence of the warrior-athlete. The competitors were nude except for a helmet and greaves, and carried a shield.
Thucydides wrote that the Spartans “were the first to bare their bodies and, after stripping openly, to anoint themselves with oil when they engaged in
athletic exercise.” Dionysios of Halicarnassos believed that “The first man who undertook to strip and ran naked at Olympia, at the fifteenth Olympiad, was Acanthus the Lacedaemonian. Plato also spoke of the old men in the gymnasiums who are wrinkled and unpleasant to the eye. Plato’s view of the old men in nude was shared by the artists of ancient Greece, whose sculptures of old men were usually clothed. Apparently the Greeks believed that the naked body of the warrior-athlete was an object upon which the adversary looked with fear and panic.
There is, also, a close connection between Heracles and this kind of nudity. Heracles has been “traditionally a nude hero” and He was the most
popular hero of the Greeks, known as alexikakos and apotropaios (an averter of evils) as strong and great, as founder of the Olympic Games, as a helper in all difficulties, as a great athlete, as the protector of the race, as an averter of death, as a nude warrior-athlete par excellence, as the hero of heroes, and as a guardian angel.
Another crucial point to mention is that in the nude sculptures, the bodies are portrayed as mathematically ideal, not realistic. In the realities of the ancient world, nude and naked were two different terms. Sculptors were kind of scientist, they had a huge knowledge in human anatomy by observing the dead bodies. Creating anatomically accurate sculptures, is a whole discipline. Every muscle, nerve, joint has to be sculpted with mathematical precision. It simply requires a lot more than a posing model.
All in all, if you'd stand as a naked statue in front of a museum owner, it'd not mean you were a pornographic figure but either a hero or a warrior or even a god.