The overall goal of this revision application is to build an interdisciplinary research team with the goal to validate and utilize a new assay for quantifying the organization of collagen within tendon that can ultimately be translated into an in vivo diagnostic tool. The goal of the parent grant is to elucidate the mechanisms governing the relationships between tendon injury and joint damage. Specifically, the hypothesis is that an increase in joint damage will be explained by overuse activity and tendon force couple disruption. Two main clinical scenarios which were outlined in the parent grant are directly addressed in these studies. The first describes an active individual with a supraspinatus tendon tear, who would like to be advised if she can return to her previous high level of activity without causing long term damage. The second describes a laborer with a chronic tear involving the supraspinatus and the infraspinatus tendons. He would like to know if he can maintain his current level of activity without surgical intervention, or if re- attachment of the infraspinatus tendon to balance the disrupted force couple is needed to prevent joint damage. The parent grant uses an established rat rotator cuff injury model to study the biological and mechanical properties of the cartilage and intact tendons after a rotator cuff injury following a return to overuse activity or return to cage activity to determine which clinical scenarios cause long term joint damage. While this grant provides invaluable information about the mechanism of joint damage, the methods employed are destructive, and as such, cannot be translated into clinical assays. The specific goal of this revision application is to quantify the structural changes in the biceps tendon caused by returning to overuse activity following a SI tear using HFUS imaging. These HFUS measures will be correlated to measures of collagen organization from our previously established polarized light method, which would validate the use of this technique. If we are able to show that these measurements of collagen organization support the mechanical findings of the parent grant, this method would ultimately result in a powerful and reliable method for non-invasively monitoring tendon health or damage accumulation for this and other studies, as well as providing a clinically transferable diagnostic tool.