| Biomechanical studies have shown that excessive breast and trunk movements affect women’s physical activity,and sports bra can reduce breast vibration to achieve breast protection during exercise.Traditionally,optical motion capture instruments are used to measure the reduction rate of breast movement while wearing a sports bra,but the effect of sports bras on trunk motion has rarely been explored during exercise.Since optical motion capture can not attain the data of trunk rotation,attitude sensors can provide a new acquisition scheme for measuring trunk motion during exercise.Therefore,based on the use of optical motion capture instruments to explore breast movement,we introduced a Bluetooth attitude sensor to explore the impact of sports bras on the trunk during exercise.Firstly,the attitude sensor was used to collect the trunk acceleration data generated by the tester wearing different sports bras at the SN point and XP point during running.The stability of the reference point was judged by the data dispersion and the trunk reference point was effectively selected,which provided an experimental basis for the selection of the trunk reference point in the breast displacement calculation.Secondly,optical motion capture instruments and attitude sensors were used to simultaneously record breast motion parameters（SN point,LBP point,LA point）and trunk motion parameters（SN point）of the test subjects wearing nine different sports bras.The breast displacement amplitude was selected as the evaluation standard of breast movement,and the change of trunk angle and angular velocity were used as the evaluation standard of trunk movement to compare the influence of sports bras with different structural characteristics on breast and trunk movement.Finally,the correlation analysis between breast displacement amplitude and trunk movement was carried out,and a breast movement prediction model based on trunk movement parameters was established,which will provide a new calculation method for the protection effect of sports bra on breast displacement.Research shows that:（1）The support strength of the sports bra does not affect the selection of the trunk reference point.Compared with the XP point,the SN point is selected as the trunk reference object,and the fluctuation of the trunk motion data is smaller and more stable.（2）The three-dimensional displacement amplitude of breasts,the variation of trunk flexion angle,the variation of trunk torsion angle,the variation of trunk flexion angular velocity and the variation of trunk torsion velocity can be effectively reduced in the state of wearing sports bra.（3）Compared with the bare chest state,there was no significant difference in the change of side bending angle and angular velocity after wearing a sports bra.The lateral bending angle and angular velocity of the trunk were not affected by wearing sports bra with different support states.（4）The influence of bras with different structural characteristics on breast and trunk movement is different.First,compared with the combination type,the three-dimensional movement of the breast and trunk can be reduced when wearing a compression sports bra.Secondly,compared with polyester,the vibration amplitude of the breast in the three-dimensional direction and the fluctuation range of the trunk can be better reduced when wearing a sports bra with cotton as the main material.Then,when the shoulder straps are designed as an I-shaped,the displacement amplitude of the breast in the front,back,left and right directions and the flexion movement of the trunk can be reduced,while when the shoulder straps are designed as a straight-back type,the breast displacement in the vertical direction and the torsion amplitude can be reduced.Lastly,in the material of the lower girdle,the sports bra composed of the lower girdle of nylon with less content will limit the displacement of the breasts and reduce the movement of the breasts and trunk.（5）The breast displacement amplitudes in the left and right and up and down directions are strongly correlated with the trunk motion parameters,but there is no correlation between the breast displacement amplitudes in the up and down directions and the trunk parameters,and sports bras with different support strengths will not affect the trunk movement.Then,the regression model of breast movement based on trunk movement parameters is established as:Y1=-2.312+2.116×X1+0.252×X4-0.163×X3,Y2=72.05-1.536×X1+0.447×X4-2.37×X2.Among them,Y1 is the breast displacement amplitude in the left and right directions,Y2 is the breast displacement amplitude in the front and rear directions,and X1,X2,X3,and X4 are the changes in the trunk flexion angle,the trunk torsion angle,the trunk flexion angular velocity,and the trunk torsion angular velocity,respectively.amount of change. |
