What should I have in mind when asking this kind of quite a delicate question? Any suggestions? Is it appropriate at all?
The fitness industry makes special clothing to deal with this sort of thing, and no matter how embarrassing or somewhat "crude" the topic may seem, I think it's a valid part of fitness. It wouldn't be disconcerting at all to see a question about how to prevent getting blisters on the hands when beginning rowing or something, but people are a little shocked or taken aback when they see questions about the genitals and such. My suggestion would be to make it as polite as possible, using proper medical terms, and leave it at that. I believe the example question you have posted in the comments of your question is adequate in that regard.