Identifying a vertical neutral position of the breast using simple measures.

During physical activity, many women suffer from breast discomfort due to excessive breast motion. It has been hypothesised that movement-induced breast discomfort is caused by straining the tissue of the breast. To understand the stress applied to the breast tissue during exercise and in turn understand the motion of the breast in engineering terms, the breasts need to be placed in a position where the tissue is neither in tension nor compression. Haake and Scurr (2010) developed a method, the lift and drop test, to locate this position and termed it the neutral position.The three-dimensional motion capture system was assessed as to whether it was capable in measuring accelerations of -1 g, in a simple oscillating system. Eight cameras, sampling at 200 Hz, captured the motion of the metal plate attached to a wooden structure by either one or two elastic cords. Accelerations of -1 g were found when the metal plate was unloaded, therefore the elastic cords were not under tension. The results showed that the system was able to measure accelerations of -1 g, however, the motion was too simple and therefore testing was needed to be completed on a women's breast.A participant (34D cup size) placed two markers on the body (right nipple and suprasternal notch). Eight cameras placed in a semi-circle tracked the markers, during the lift and drop exercises. The maximum negative acceleration found during the exercise was -0.64 +/- 0.04 g. The lift and drop exercise was deemed inappropriate in locating the neutral position. Therefore, further work in identifying an appropriate method in locating the neutral position was required.Seven participants with breast sizes ranging from 34A to 36D placed three markers on their body (right and left nipple and suprasternal notch). Ten cameras tracked the markers during running (10 km.hr[-1]); stepping off a low box (0.26 m) and a high box (0.51 m); vertical countermovement jump; and lifting and dropping the right and left breast.The vertical countermovement jump forced the breasts to oscillate nearly one and a half times (1.3 +/- 0.2), causing the breasts to move through a neutral position multiple times in a single trial. During a single trial a higher and lower neutral position was recorded. The accelerations between these positions were -0.13 g and -1.80 g and therefore the neutral position was reconceptualised as a neutral zone. The exercise also produced low discomfort scores of 0.6 +/- 0.7.Breast motion during running (10 km.hr [-1]) and walking (4 km.hr[-1]) of a participant with a breast size of 34A was used to demonstrate the effects of breast motion with respect to the neutral zone and perceived breast discomfort. The work showed that breast discomfort was reduced when wearing a sports bra compared to no support. This could be due to 1) the magnitude of vertical breast displacement being reduced; 2) breasts lifted closer to the neutral zone; and 3) level of breast support increased.This research indicates that the previously defined vertical neutral position, should instead, be considered a neutral zone defined by upper and lower boundaries, which are found most effectively by performing a countermovement jump. The vertical neutral zone could allow for greater understanding of the stress applied to the breast tissue during movement which in turn could inform the design of bras.