Of course breast movement affects stride! I remember as a teen (a 34B teen, mind you) running down the stairs in the morning (braless) and needing to grab my breasts and hold them to my chest to keep them from throwing me off balance!

I take little to no notice of them with a bra on...but bras are a relatively modern enhancement.

I'd be curious to see if running barefoot would change the results of the above study. They've already shown that humans strike the ground harder with shoes on than they do barefoot. So if women ran without shoes, would the breast movement be decreased as the feet and legs did more to absorb the impact as they should?