NOT A MYTH! I saw it's effects first hand when I went and watched Claire run her marathon.
Let's first read one man's experience:
"Whenever I go out for a run longer than 45 minutes and I don't protect my nipples I know I am in for trouble. First time this happened to me I was quite shocked. During my long run in the dark I felt my nipples starting to hurt. A stinging sensation. Not much to do about it when you are running! I ended up holding my shirt the last twenty minutes so that it didn't come into contact with my nipples anymore. When I got home I got a good look at my shirt and was shocked to see part of it was covered in blood. My nipples were bleeding. That was my first and painful experience with nipple chafing while running. Afterwards I haven't had the experience many more times, because I took protective measures."
Now lets explore more about this:
Nipple chafing is the result of friction between your chest and your shirt. It mostly effects men and only some of them. "Treat your bleeding nipples like a normal open wound. So wash them with water. Then clean them with an antiseptic and then cover them with a sterile gauze pad. Protect your nipples the next times you go running, because I can tell you that they stay tender for a very long time. The chances of them getting chafed again are quite high!"
So how can you protect you nipples?
1. Use bandaids, but there are some cons to using bandaids namely it doesn't stick to chest hair very well, when you sweat it can fall off and you can be a manly man, but it's going to hurt to take off.
2. Use cream, but if you're going on runs longer than an hour you might have to take it with you because after a while the effects wear off.
3. Use nipguards! Click here for more information about nipguards!
You're probably wondering if I have had any experience with nipple chafing. All I can say is wear a water shirt when boogie boarding. This may be able to prevent rashes and nipple chafing. When running you can probably prevent nipple chafing by going shirtless like Matt Brigham sometimes does.