Running with breasts, a weighty issue

Recently, I received an email from Inside the Games, an online newsletter used to keep people up-to-date on the London 2012 Olympics and other events.  It had the following headline:

Rawlinson removes breast implants to help win Olympic gold in London

With only this to go on, I was confused because the only Rawlinson I could think of was Chris Rawlinson the male Commonwealth gold medalist in the 400m.  Momentarily my mind raced away with questions: Has he come out of retirement? Has he got implants? Why? Of course he should remove them, they could only be a hindrance to running surely?

Figure 1. Jana Rawlinson earlier this year

How foolish did I feel when I clicked on the link and saw the photograph of Jana Rawlinson his wife!  But wait a minute, surely my ridiculous thought about breasts being a hindrance for Chris must be equally valid for Jana too?  Jana is having her implants removed to avoid jeopardizing her chances of a medal in London for the sake of ‘her own vanity’ (her own words).  What is the likely performance issue relating to breasts?  Does size matter?  If so, can you do anything about it?

Figure 2. Dr Jo Scurr (left) carries out biomechanical analysis of a runner.

The bounce

One person I’ve been working with and who really ought to know is Dr Jo Scurr at the University of Portsmouth. Jo has worked with women of different shapes and sizes on behalf of many of the world’s leading sports bra manufacturers, seeking the appropriate support for appropriate conditions. The research requires women to be marked up using passive markers to their body and breasts while running on a treadmill.  A multi-camera system (such as Vicon or Motion Analysis Corporation) tracks the markers and gives the results either as an animation or coordinates in 3D.  At the risk of bringing your attention to one particular bra manufacturer, Shock Absorber’s ‘bounce-ometer’ more or less gives you an idea of what goes on when a woman runs.

Figure 3. Vertical displacement of the nipple and the suprasternal notch (the top of the sternum) for a woman running at 13 km/h.

If you’ve just looked at the bounce-ometer then you’ll have realized quite how much the breasts move during even small amounts of exercise, especially for larger women.  Figure 3 shows a set of  results for a woman running at 13 km·h-1 on a treadmill.  The graph shows the vertical movement of the upper body (identified as the suprasternal notch or the sternum) and the breast (identified as the nipple) for 3 footstrikes.  The body moves up and down at about 3 Hz (3 times per second) as the woman runs in a relatively symmetrical fashion and with an amplitude of around 50 mm (2 inches).

The breast, on the otherhand, overshoots the upper body so that it reaches its maximum displacement of over 80 mm after the body has already started to move in the opposite direction.  This happens on both the upward and downward bounces.  The fact that the breast mass is moving one way while the body mass is moving in the other stretches the skin and tissues supporting the breast and can lead to stretch marks and pain.  The stretching is exacerbated by the vigour of the exercise and by the mass of the breasts.  It can be alleviated by good support, which we shall come onto later.

The physicist’s view

At the risk of appearing like a contestant on Beauty and the Geek I’m going to think about the physics of the breast while running.  Given that the primary purpose of breasts in women is lactation, much of the breast mass is pretty redundant when running and any mass that is not linked to power generation is bad for acceleration.  Newton’s second law tells us that acceleration is inversely proportional to mass so that the higher the mass, the lower the acceleration for a given propulsive force.  The mass of a C-cup breast, is somewhere around 300-400 g (10.5 to 14.1 ounces)1, representing around half a percent of the mass of a typical female runner.  At the very least, then, the extra mass will reduce the acceleration by half a percent; this might not sound like much but could affect the medal places for an elite athlete.

What about the bounce?  Figure 3 shows that the breast can displace more than the upper body by over 25 mm (1 inch) and the subsequent stretching of the skin and internal tissues of the breast can cause significant pain.  This is enough to stop some women ever going near exercise at all. Even if there is no pain, moving a 300-400 g mass up and down 3 times a second for 400 m must take up energy, some of which could be put into running faster.

To enhance or not to enhance

When it comes to Mrs Rawlinson and her implants dilemma, the question is whether to enhance her performance or her body.  From the cold physics point of view, it appears that breasts do really get in the way of performance and so the decision to remove implants is the right one.   And she is not alone, Simona Halep has had surgery to reduce the size of her natural breasts to help with her tennis, while many women in the UK and worldwide seek to have their breasts reduced in size to improve their quality of life.  But for those women not engaged in high performance sport, and not necessarily in need of breast reduction surgery, the solution comes from the work of  Jo Scurr and others: encapsulated sports bras support each breast (as opposed to compression bras which squash the breast close to the chest wall) and can limit the additional vertical motion of the breast mass causing the stretching to a matter of 5 to 6 mm, even for women with large breast sizes.

Of course there are ethical and moral issues in breast reduction and hospitals in the UK have strict rules on eligibility.  The decision for Jana Rawlinson is much easier; she put the implants in in the first place and is absolutely entitled to take them out again if she wants to.  Good luck to her – I shall certainly be paying special attention to the women’s 400m in London in 2012.

1Turner AJ and Dujon DG (2005) Predicting cup size after reduction mammoplasty.  British Journal of Plastic Surgery 58:290-98.

About stevehaake

Steve is Professor of Sports Engineering at Sheffield Hallam University. He has a degree in Physics from the University of Leeds and a PhD from Aston University on the mechanics of golf balls on golf greens. He has over 200 publications, including his first book "Advantage Play: Technologies that changed Sporting History" due out in October 2018.