While there is not a great deal of literature investigating the use of external cues for visual feedback during exercise or assessment using lasers, there are resources that can link the application of the Motion Guidance device to science. One such example is found in the article by Balke in the Archives of Orthopedic Trauma Surgery in 2011. This article investigated the changes in joint proprioception of the shoulder in healthy controls and subjects who had diagnosed shoulder instability. 

Stability in the shoulder joint is mainly provided by muscles and tendons little bony reinforcement, therefore proprioceptive function seems to be critical and of high importance for ADL's in this area. One common hypothesis for altered shoulder awareness involves changes in sensorimotor function after injury. This article hypothesized that changes in the quantity of shoulder capsule distension give inaccurate feedback to the brain via muscle spindles and Golgi Tendon Organs, thus effecting muscle coordination and pulley systems around the shoulder. Balke's study outlined the subjects to have a laser pointer attached to the wrist and determine position sense by having subjects establish norms with visual feedback at 55*, 90*, and 125*. Next the vision of the subject was covered and then asked reproduce the same joint positions and these were recorded. The procedure was repeated 3 times for flexion and 3 times for ABD. The results were significant. Reproduction of the same angle was worst in the instability group at 55*. This is hypothesized to be contributed to slack of the capsule at said range of motion. However, the instability group also showed significant differences at 125*. The capsular tension at this range would be increased. But it is also well know that scapulothoracic motion also contributes to achieving this motion. This this raises the question of whether muscle coordination or sequencing could be altered above the shoulder height as well in the unstable shoulder. Groups were equal and numbers were not significantly different at 90* and this is well supported in previously documented research studies in the literature. 

This article gives some direction and excellent clinical application for use of the Motion Guidance device. Not only can the MG be fastened to the wrist or upper arm to reproduce the exact set up of this study, it also can be implemented in treatment by utilizing the flag grid that is available with the Clinician Kit. A patient could be set up for both flexion and ABD while receiving real time feedback on shoulder joint position and needed corrections of altered proprioception. A clinician might also be inclined to ensure that their patient is performing proprioceptive feedback exercises below AND above shoulder height rather than only at 90* based on the result of the study. To enhance motor learning between session, the MG patient pack could be issued to patients for home use. 

Remember, moving forward with science...