Non-linear finite element model to investigate large skin deformation of women during yoga exercise for bra design

Large skin deformation in Yoga exercise requires clothing designed with a high degree of fit and conformity to avoid fitting problems, pressure discomfort or the shift and slippage of the clothes. This study aimed to explore the skin deformation of the upper body during arm abduction for optimizing the elasticity distributions of yoga bras, to match the skin deformation distributions. A finite element (FE) model based on motion capture experiments was developed to simulate skin deformation during arm abduction from 20° to 170°, and the skin deformation in three directions (X: anterior-posterior, Y: medial-lateral, Z: vertical) and the total deformation at the abduction angles of 20°, 50°, 90°, 130°, and 170° were analyzed. The results revealed that the skin of the upper body primarily stretched in direction Z (highest displacement range of the isobands: 67.89 ∼ 82.67 mm at 170°) and Y (highest displacement range of the isobands: 47.09 ∼ 64.84 mm at 90°), with the distribution of gradient descending stretching deformation from the lateral to the medial areas of the upper body during arm abduction. In contrast, only limited compressive deformation was found in direction X, centered around the breast, shoulder and the lateral back areas. The total displacement increased with the arm abduction angle, and exhibited a gradient decrease from the upper lateral areas (highest total displacement: 79.07 mm) to the lower medial areas (lowest total displacement: 14.68 mm) at the angle of 170°. Based on the total displacement isolines, an elasticity-distribution bra featuring a gradient of decreasing Young’s modulus in both the warp and weft directions for the medial-to-lateral areas was developed. These findings provide novel information for yoga bra design and are expected to benefit the sports bras industries and exercising women.