Architectural gear ratio and their accompanying tendons. These muscles form a cuff around the glenohumeral joint and function to stabilize and manipulate the shoulder. The pennation angle of the rotator cuff myofibers, the angle at which fibers connect to the associated tendon, affects the contractile properties and function of the whole pennate muscle. For example, the pennation angle determines the architectural gear ratio at which a pennate muscle operates. A large initial pennation angle results in a large AGR and velocity amplification. A 2011 study on human cadaveric shoulders suggests tendon tears may affect the pennation angle of the rotator cuff muscles. Researchers
Rotator cuff tear in frequency with age and the most common cause is age-related degeneration and, less frequently, sports injuries or trauma. Some risk factors of experiencing a rotator cuff tear cannot be changed: age, body mass index, and height. Recurrent lifting and overhead motions are at risk for rotator cuff tears. People who have jobs that involve overhead work, such as carpenters, painters, custodians and servers are at risk of also experiencing a rotator cuff tear. People who play sports that involve overhead motions, such as swimming, volleyball, baseball, tennis, and American football quarterbacks, are at a greater risk of experiencing a