It　has　been　a　long-standing　problem　in　the　engineering　design　of　bra　for　optimal　support　and　shaping　due　to　the　difficulty　of　quantifying　the　hyper-elastic　properties　of　human　breasts.　The　objective　of　this　study　is　to　determine　an　optimal　approach　to　obtain　the　non-linear　properties　of　breast　soft　tissues　and　the　corresponding　deformations　during　motions.　The　Mooney-Ftivlin　material　parameters　of　the　breasts　in-vivo　were　verified　through　an　optimization　process　that　involved　iteratively　changing　the　material　coefficients　with　the　integration　of　static　and　dynamic　finite　element　models.　Theoretical　equations　of　a　rigid-flexible　coupled　system　during　the　motion　of　forward-leaning　were　established　with　gravitational,　centrifugal　and　Coriolis　forces　to　simulate　the　dynamic　deformation　of　the　flexible　breasts.　The　resultant,　optimally　generated,　coefficients　of　the　Mooney-Rivlin　hyperelastic　material　type　for　the　breast　were　found.　This　new　set　of　breast　material　coefficients　was　verified　by　finite　element　analysis　of　the　breast　deformation　during　forward-leaning　and　running　movement.　The　method　proposed　in　this　study　provides　an　effective　way　to　determine　the　breast　properties　for　predicting　breast　deformation　and　analysis　of　the　bra-breast　contact　mechanism　and　thus,　improving　the　design　of　bras.