So I ask you, ney I beg you - strap your boobies down!!!
Boobs, Baps, Boobalas, Tits, Melons, Fried Eggs, whatever you call them, get some support on them if you are doing sport. Its incredibly important that you do strap them down correctly, as the long term damage in undoable.
Your boobs are made up of a layer of muscles (Pectorals) then all the important bits as well as layers of fat. This is all covered by skin that is thinner than on other parts of your body. This muscle underneath helps with the pertness of the boobs, but thats no good if you've gone and damaged the connective tissue on top - the only way of protecting them is with a correctly fitting, supportive Sports Bra.
Images from http://www.sportsbras.co.uk
You can pick up a decent sports bra for as little of £20 - some of the best out there are by Shock Absorber, you don't need a plunge style - compression is better, especially if you have extra boobage!
So, please lovely reader, protect your boobies as you really do not want to ever give your self, or other gym goes a boob related black eye.
Do you correctly control your boobies?