Few anatomical structures hang outside of the body unsupported by cartilage, muscle, or bone—meaning there wasn’t much historical research to build on. Wakefield-Scurr’s lab was the first to find that when women run, the motion of the torso causes breasts to move in a three-dimensional pattern—swinging side to side and up and down—as well as moving forward and backward. In an hour of slow jogging, boobs can bounce approximately 10,000 times.