Current sports bra designs often overlook the evolving breast development of adolescent girls during puberty. Inadequate control of breast motion and excessive compression are frequently reported with the use of sports bras. This study aims to address these issues through 3D knitting structures for extensible bra cups and breast protection to specifically meet the needs of adolescents. Sport bra designs have been developed to meet the specific requirements of adolescent girls. In contrast to the current tank top designs that continue to neglect breast growth and protection required during physical activities, these bras are adjustable to accommodate the rapid growth of breast size during adolescence, offering an aesthetic and comfortable way to cope with the inevitable changes in their bodies. The findings will have a positive long-term impact on the increasing number of adolescent girls who strive for a healthy and active lifestyle by engaging in physical activity.