The best way to choose a sports bra is to get expert advice. There are now specialist retailers in the UK such as www.lessbounce.com who can talk you through the details by phone or by email.
You should not buy your bra based on a measurement of your bust size. Bras from different manufacturers are not all the same size. Your measurement may have been done badly, or your bust size may have changed (especially if you increase your training, which tends to reduce your cup size). Your optimal fitting can also vary over your menstrual cycle (because of water retention). Instead you should try the bra and choose one that is comfortable for you and which fits you snugly. Check that there are no seams or clips that will irritate your skin over a long run. Jump up and down – your breasts should hardly bounce at all. Make sure that the base of the bra will not ride up over your breast while you are running, but that it is not so tight that it is difficult to breathe easily. You should also find out whether the shoulder straps dig in.
After running, particularly on long runs, some women have sore skin either between the breasts, across the back under the strap and buckle, or along the line of the base of the bra under the breasts. This friction can be reduced by liberal application of Vaseline, or some other lubricant, on these areas under the bra before you start running.
A crop top is not the same as a sports bra, and many of them don’t provide the support you need. However, there are some sports bras that are designed to look like crop tops so that you can run in them without a t-shirt over the top.
