A cycling tech analyst comments about runners (sprints).http://velonews.competitor.com/2016/08/bikes-and-tech/technical-faq-saving-freehubs-aero-is-everywhere_418864
I think it is particularly interesting given your example of the US women’s 4X100 relay team, because my wife and I frequently wondered aloud to each other while watching the speed events on the track — the ones with starting blocks, whether running or hurdling — about what big hair some of the competitors had and how it seemed sure to be slowing them down. I can imagine a boundary-layer effect in that instance, too, but it’s very hard for me to imagine that some of the huge hair on some very fast Jamaican and American sprinters wasn’t, on balance, slowing them down, and not just from aerodynamic drag, but sometimes also from having to accelerate all of that additional mass.