Maybe you've noticed someone near you is experiencing enlarged breasts--it's been known to happen during pregnancy and after giving birth, especially if there's breastfeeding involved.
Now you can precisely quantify the amount of incremental bounce-age for those new breasts, thanks to the Shock Absorber Bounce-o-meter, a computer simulation produced by a UK sports bra manufacturer. Just input the cup size, and the activity level (from yoga to horseriding, but no "staggering to kitchen on two hours sleep"). Then repeat for the newly engorged breast size and watch the difference in either Lara Croft-style CG or scientifical wireframe versions.
The Bounce-o-meter data is based on the University of Portsmouth's 2004 Shock Absorber Breast Movement Study. The University reports that the intern waitlist for the Summer 2007 followup study is full.
Related: my wife swears that the only actually good, comfortable, useful nursing bra is by Bravado. The rest gave her a heck of a time.