I was out running a few years back and after a few long runs I noticed that the click on piece that attaches to my heart rate monitor strap was rubbing against my chest causing untold discomfort. So I went into a few Google forum’s and found a good tip and costs nothing but the price of band aid or elasto plast strips. As you can it might look weird but this is only the top and the bottom isn’t completely covered because if I did that I wouldn’t have been able to attach it to the strap.
This picture below is how the hrm looks underneath.
It might look very rustic and rough but it works and costs nothing at all I always have Elastoplast/bandaid handy because I do suffer from nipple chafing from time to time.. Hopefully this little tip I picked up will help you..and keep you running with less discomfort..