Одежда, напоминающая бикини, использовалась женщинами для занятий спортом ещё в Древнем Риме.

Famous "bikini girls" mosaic (found by archeological excavation of the ancient Roman villa near Piazza Armerina in Sicily), showing women exercising, running, or receiving the palm of victory and crown (for winning an athletic competition).
Bikini Mosaic
Villa Romana del Casale
M. Disdero