The Impact Of Diverse Intensities Of Step-up Movements On The Kinematic Characteristics Of Breast

Purpose and Significance:The purpose is to analyze the causes of breast pain from the perspective of sports biomechanics.The significance of the research lies in a new form of exercise is used to study the movement characteristics of the breast in the vertical direction,providing a theoretical reference for exploring the mechanism of pain and optimizing the design of sports bras.Methods:Nineteen women(10 in B cups and 9 in C cups)performed step-up exercises with bare breast at two heights(11cm and 31cm),keeping the dominant leg as the start-leg to up and down steps.Participants were required to gradually increase the frequency of exercise from a static state.When experienced breast pain during this process,maintain the frequency of exercise to complete 5 exercises,then adjusted to a painless frequency and maintained the frequency of exercise to complete 5 exercises;If the participant had reached her maximum exercise frequency while did not feel pain,the test of this subject at this height would be not be included in subsequent analysis.At each height,participants who experienced breast pain was analyzed,and the kinematic difference of breast and trunk between her pain and painless state were analyzed.Using the 8-lens Motion Analyze Raptor-4 infrared light spot high-speed motion capture test system to collect kinematic data of fluorescent markers on the subjects’ body.Using Helen Hayes model to attach markers,in addition,plus 6 points(the left and right nipple points,sternum corner point,sternum angle contour point,the 7-8th thoracic vertebra point and the 7th cervical vertebra point.The original data is processed in Cortex software with a cutoff frequency of 13 Hz.A coordinate transformation was used to convert the nipple point coordinates to the coordinates in the trunk coordinate system.Analyzing step-up frequency,the maximum increase percentage in chest-breast distance,and the maximum values of velocity and acceleration in the upward and downward directions of nipple points of the dominant side(in the standard system)and sternum corner points(in the geodetic coordinate system)of five step-up cycle in both pain and painless state.Chi-square test is used to analyze the pain probability of different cups.In each height,using paired T test to analyze kinematic index of pain and painless,significance level was set to P<0.05.Calculating Cohen’s d effect size(<0.2,small;0.2-0.5,medium;>0.8,large).Calculating Spearman correlation between each index and pain parameters,significance level was set to P<0.05.Results:There was no difference in the incidence of breast pain among women with B and C cups(P>0.05).When stepping up at a height of 11 cm,the main difference between pain and painlessness was the maximum downward velocity of the nipple(pain 0.75±0.18m/s,no pain 0.39±0.15 m/s,P<0.01,d=2.17),followed by the nipple point displacement(pain 4.6±1.2cm,painless 2.5±1.0 cm,P<0.01,d=1.79).The maximum upward velocity were most strongly associated with pain(r=0.868,P<0.01),acceleration was the least strongly associated(r=0.620,P<0.01),and the maximum increase percentage in chest-breast distance were unrelated with pain(r=0.372,P>0.05).When stepping up at 31 cm height,the main difference between pain and painlessness was the nipple point displacement(pain 5.4±1.8cm,no pain 3.7±1.4cm,P<0.01,d=1.11),followed by the maximum downward velocity of the nipple point(pain 0.85±0.32 m/s,painless 0.57±0.18 m/s,P<0.01,d=1.08),there are no difference in acceleration parameters(P>0.05).The maximum downward velocity of the nipple point were most strongly associated with pain(r=0.711,P<0.01),displacement magnitude of nipple point was the least strongly associated(r=0.468,P<0.05),and the maximum increase percentage in chest-breast distance were unrelated with pain(r=0.208,P>0.05).Conclusions:(1)In step up exercise,for women with cup sizes B and C,the incidence rate of pain in C cup women did not larger than B cups.(2)The causes of pain at different heights are slightly different.The main reason for incidence of pain at 11 cm is the excessive maximum upward and downward velocity of nipple point.The main reason for incidence of pain at 31 cm height is the excessive maximum downward velocity and displacement of the nipple point.(3)The main cause of breast pain is the excessive vertical velocity of breast relate to the trunk.