[5kywalker]

Just before the start the runners hydrate, then nerves cut in and if it is a long run the lack of facilities on the way forces the runners to find anywhere semi-private near the start. One bold female is the first to semi-hide behind something, squatting down and pushing her muscles to force out the contents of her bladder in the minimum of time. The others, know what she is doing, join in one. Also squatting down close by, on the basis that they don't have to be embarrassed if some one else is peeing also. The observer with an interest the the shape of female buttocks is able to compare the various shapes and to pick out a high percentage of callipygian females.