Estrogen has a dramatic effect on musculoskeletal function. In the past, much of the research focus has been on the strong connection between estrogen and bone. However, recently the effect of estrogen on other musculoskeletal tissues such as muscle, tendon, and ligament has become the focus of more research. These studies make it clear that estrogen improves muscle proteostasis and increases bone density; however, the benefits to bone and muscle come at the cost of decreased connective tissue stiffness. Evolutionarily, this makes sense since laxer joints and better repair following injury would facilitate healthy childbirth and recovery. However, as more women participate in sports, these physiological effects of estrogen contribute to decreases in power and performance and make women more prone to catastrophic ligament injury. To promote female participation in an active lifestyle throughout their life span, more research is needed to determine how nutrition, training, and hormonal manipulation can be used to promote optimal performance at any age. Another hormone that affects sinew is Testosterone (T). In rats, supplementation with T results in stiffer tendons that absorb less energy before failure. In humans, the ratio of E2 to T is negatively correlated with ACL stiffness, suggesting that E2 overrides the effects of T in female ligaments. Further, women treated with aromatase inhibitors, that prevent the conversion of T to E2 commonly report musculoskeletal pain and experience tendinopathies, suggesting that the interplay between T and E2 is essential to sinew function. The overall goal of my dissertation is to define the effects of hormonal manipulation on sinew function, with a specific focus on collagen synthesis, incorporation, and degradation using a 3-D engineered human ligament model.