This study assesses the effectiveness of an innovative shoulder training and rehabilitation device, the Rotr 1. The device uses mechanically created motion to disturb the balance of muscular forces around the shoulder, thereby facilitating dynamic training of the muscles. The hypothesis is that random disturbances provided by the device would potentially in-crease shoulder muscle activation as users try to resist the device’s motion. To test the efficacy of the device, shoulder muscle activation from two groups (ten non-athletes and seven athletes), was assessed in three different shoulder positions and four different exercise conditions (aka configurations). Muscle activation of seven different shoulder muscles was recorded using electromyography (EMG). 3D motion capture was used to ensure repeatability of the positions during testing. ANOVA was done to assess the differences in muscle activation across groups, positions and exercise conditions. This device has the potential to improve performance and rehabilitation of overhead athletes, by increasing the body’s ability to effectively react and protect the shoulder.