A while back, when gyms were open, I lead a seminar on the importance of spinal alignment and ways to incorporate strengthening posture muscles into a work out. I had some time to kill so I spent a bit of time people watching.
I noticed two young women on treadmills at either end of a bank of treadmills. Both women were wearing what had to be Victoria Secret 'fashion' bras. There was a whole lot of bouncing going on - I'm dating myself, but think Bo Derek running on the beach in the movie "10".
Both women were quite large chested and were moving a long at a nice pace. Some fellows in the free weight area were sneaking glances at them but at one point the guys looked like they were watching Roger Federer at the Australian open. Right, left, right, left and so forth.
It is possible the women were unaware of the attention, but one thing is sure: Running unsupported is NOT good for breast tissue, the upper back or the neck.