After having a very interesting discussion the other day with one of my fitness friends about why ladies do not use their arms to run properly- I had a thought that I would try and convince a few more people to take it seriously. I do a lot of biomechanics analysis and this is something I do not take great pleasure in pointing out! - the way you swing your arms (or do not) is directly dependant on how good a bra you are wearing!!! If you are too busy holding your top box to use your arms to propel yourself you are inadvertently slowing yourself down and fixing your trunk to stop your boobs bouncing up and down.
If you need some convincing here is the research about how much you are bouncing!!
During walking, a woman's breasts move the same amount in and out, up and down and from side to side: about 33% in each dimension.
Up the pace to a jog or a run, and the movement is split: 51% up and down, 22% side to side and 27% in and out. The overall pattern is a figure of eight (on it's side).
Breasts move as much during a slow jog as they do during a sprint, meaning no matter what your pace, you should always wear a sports bra- and a good one at that! Two ordinary bras will not stop the motion.
If you are hitting the ground hard then you are getting alot more vertical bounce than you would ever want- damaging breast ligaments and altering your whole body biomechanics and a lot more besides!( AKA heading south!)
Warning- clicking here http://www.shockabsorbersport.co.nz/wawcs0141481/bounce-o-meter.html will make your eyes water! Put your size in and your sport and see how much damage you could be doing! Enough said!