It's the stuff to give a teenage boy a case of the nervous giggles.
Bouncing boobs. Jiggling breasts.
But it's not a laughing matter for the women who just want to work out without a pain in the chest.
Scientists are finally examining the effect the fun bags have on your form, and it isn't pretty.
In a report out of the University of Portsmouth's Department of Sport and Exercise Science, researchers have determined "inadequate breast support affects a female's running kinetics, which may have negative physiological consequences on sports performance."
The bouncing of the boobs while you run isn't just uncomfortable, they found, it can cause stress injuries.
And despite your attempt to maintain proper alignment, the larger the breasts, the more likely they will throw off your balance ever so slightly -- paving the path to injury.
It isn't just running. I studied karate for several years with a woman who was significantly more well-endowed than I, and I had the unique angle of watching how easily they get in the way of physical activity.
In sparring, I had better form simply because I'm flat as a pancake -- and I could glide my arms across the front of my body without something inhibiting the movement.
Some of this can never be changed -- at least without surgery -- but there is some good news in all of this. Adequate support in the form of sports bras is out there.
And all that back pain from your big breasts can be relieved with some good techniques.
Have you held back on a workout because of your breasts?
Image via lululemon athletica/Flickr