Summarize the following in your own words: The risk of developing a degenerative rotator cuff tear increases dramatically with age, reaching over 50% in the 7th decade of life. The severe pain and loss of function brought on by rotator cuff tears underscore the importance of swift and effective treatment. Unfortunately, failure rates for treating rotator cuff tears remain high. Unsuccessful treatment may relate to failure to restore joint kinematics or propagation of the rotator cuff tear. Furthermore, it is not clear which types of tears (i.e., geometry and amount of degeneration) will result in propagation. Therefore, the objective of this work was to investigate the effects of exercise therapy and initial tear characteristics on alteration of glenohumeral kinematics and tear propagation. Glenohumeral joint kinematics were measured in subjects with an isolated supraspinatus tear before and after 12 weeks of therapy. Although exercise therapy does not increase sub-acromial space, therapy decreases the overall joint contact path length by 36%, indicating a more stable joint. Cadaveric experiments measured tear propagation for increasing levels of loading using a novel cyclic loading protocol. Anterior supraspinatus tears propagate at lower loads than tears in the middle third (389 ± 237 N vs 714 ± 168 N). Mechanical testing also showed that tendons with preexisting rotator cuff tears are not more likely to propagate than artificial tears representative of a "traumatic" rotato.