I know that male swimmers tend to do that -- something about less drag as they move through the water. But I don't know what the functional purpose of shaving hair would be for male gymnasts. Is it easier to do some movements when skin can glide against skin rather than over hair? Do they disipate body heat faster from hairless skin rather than with hair? Or, could it be for cosmetic reasons? Do they seek to impress with their muscle definition, unshielded by hair?