PROJECT ABSTRACT Histological studies showed that the degenerative process following rotator cuff tears goes beyond the mere accumulation of fat and includes diminished functional contractile tissue and altered perfusion. Histological measures are limited in clinical studies due to the invasive methods (biopsy) necessary to sample tissue. Quantitative magnetic resonance (MR) imaging and spectroscopy can measure the degenerative process in skeletal muscles, track disease progression and therapeutic efficacy. MR imaging-based Blood Oxygen Level- Dependent (MRI-BOLD) and 31phosphorus MR spectroscopy (31P-MRS) are reliable estimates of muscle microvascular function and energetic status, which are makers of muscle function and quality. Alterations of MRI- BOLD and 31P-MRS are related to lower extremity weakness and decreased gait performance associated with aging, as well as the degeneration associated with pathological disorders of skeletal muscles. Thus, MRI-BOLD and 31P-MRS offer advantages over measures of muscle function and quality that require tissue sampling. These markers may enhance the mechanistic understanding of the degenerative process following rotator cuff tendon tears, and may provide quantitative measures for treatment efficacy, which is of the utmost importance considering the recent advent of biological augmented treatment approaches. Ultimately, they can positively impact the care of over 4.5 million Americans who seek treatment for rotator cuff tears each year. This project will use MR-derived markers (MRI-BOLD, 31P-MRS) to investigate microvascular function and energetic status of the supraspinatus in 30 individuals with full-thickness supraspinatus tears, the most commonly torn rotator cuff tendon. Thirty age and sex-matched individuals without shoulder pain or imaging evidence of rotator cuff tears will be recruited as controls. This project has three specific aims: 1) Develop a dynamometer to measure shoulder abduction force in real-time during MR scans; 2) Test the hypothesis that post-contractile MRI-BOLD response and energetic status evaluated with 31P-MRS of the supraspinatus differ between patients with full- thickness supraspinatus tendon tears versus control individuals; and 3) Test the hypothesis that the MRI-BOLD response and energetic status of the supraspinatus predict shoulder function and abduction strength in patients with full-thickness supraspinatus tendon tears, after accounting for the variance predicted by sex, pain, and fat accumulation. Completing this study will advance the field of quantitative imaging by providing non-invasive measures of muscle vascularity and energetic status in individuals with full-thickness supraspinatus tendon tears. These measures will advance the understanding of the degenerative mechanisms after rotator cuff tendon tears. Future clinical research will evaluate the impact of supraspinatus degeneration/regeneration on patients’ symptoms and the efficacy of promising treatment ap...