The strange thing about gym wear

[Bede735]

Off topic, I know, but there's usually a gym in the same complex as a swimming pool, so I'm quite aware of it. So, what I've found is - women invariably wear sleeveless tops, while men wear short-sleeved t-shirts.

Now why is that? If men are comfortable not wearing a top at the pool, why don't they wear a sleeveless top at the gym? Is it not a more practical garment to work out in? Or does wearing something like them signify gayness?