I was doing a long run on a treadmill last Sunday.
This is not a common occurrence for me, but my "A" race of the season is a net downhill half marathon, and this specific treadmill can decline.
The theory of race specificity dictates to train similar to the race settings, so I did a downhill two hour progression run. Yes, my quads felt it the next day.
Anyway, back to the point at hand, which was the lady on the treadmill next to me.