This study investigates breast biomechanics during physical activities, aiming to evaluate the magnitude of breast tissue acceleration using different modalities.We aim to compare existing methodologies for evaluating breast movement by comparing acceleration data derived from 3D motion capture marker displacement of the nipple-region and triaxial accelerometry data collected from multiple breast regions. Twenty female participants, with cup sizes ranging from D to H, engaged in a series of physical tasks while wearing different types of support, ranging from conventional everyday bras to sports bras designed for full-busted women. Triaxial accelerometers consistently indicated higher acceleration magnitudes, potentially due to their ability to detect localized movements that 3D motion capture may smooth out during data post-processing. Our findings suggest that when breasts are well-supported by a sports bra, external triaxial accelerometry markers accurately reflect breast tissue acceleration. This reinforces the reliability of sports bras in ensuring uniform support and highlights the need for standardized breast biomechanics measurement protocols. The findings of this study may be used to help optimize sports bra design as well as the refining of breast biomechanics measurement methodologies in women with larger bra sizes.