Female breast motion during exercise based on the Lagrange method

Breasts can move considerably when women are active, which can sometimes be uncomfortable. Many studies have measured breast movement by a camera recording the movement of multiple markers attached to the breast. However, an excessive number of markers may hinder the subject’s movement. Additionally, camera images cannot readily distinguish closely arranged LED markers owing to interference of light from the markers. Therefore, it is necessary to develop a numerical model to minimize experimental limitations. The present numerical model was developed based on the Lagrange method to enable simultaneous prediction of the movement of multiple positions on the breast during successional vertical jumps. The modeling results revealed the nipple demonstrated a larger displacement (average displacement ≈ 52.73 mm) than other marker positions during successive jumps. The breast top showed lower displacement (average displacement ≈ 46.18 mm) than other marker positions. The model also revealed the force variation on the breast during a jump. The whole breast movement was dependent on a combination of multiple forces. The viscoelastic force provided resistance to breast deformation. The restoring force drove the breast upward, while the gravity force pulled it down. The model synchronously calculated the displacements of more than 30 positions on the breast, then exported the vertical movement path of the whole breast. The model can only predict the vertical displacement and force; it still needs to be improved in other directions.