Comparison of the kinematics and kinetics of shoulder exercises performed with constant and elastic resistance.

Background: Internal and external rotation exercises of the shoulder are frequently performed to avoid injury and pain. Knowledge about the motion and loadings of the upper extremities during these exercises is crucial for the development of optimal training recommendations. However, a comparison of the angles and corresponding moments in the upper extremities that are achieved during internal and external rotation exercises for the shoulder by using different resistance types has not yet been performed. Therefore, the aim of the study was to examine upper extremity kinetics and kinematics in 3D of the internal and external rotation exercises.

Methods: The kinematics and kinetics of 12 participants while they performed 10 different exercises with a constant and with an elastic external load corresponding to 2% body mass was assessed. The motion of the upper extremities was recorded three-dimensionally with a motion capture system, using a newly developed marker set and joint coordinate systems with 28 markers. The applied external load was measured with a load cell placed in series with the external resistance, and moments were calculated using an inverse dynamics approach.

Results: The range of motion and the joint loading was highly dependent on the exercises. The range of motion in the glenohumeral joint did not differ significantly between the two resistance types, whereas internal/external rotation moments were significantly higher with constant resistance than those with elastic resistance.

Conclusions: Larger or lower moments can, therefore, be achieved through selection of the appropriate resistance type, while the range of motion can be altered through the selection of exercise type. Therefore, the loading motion patterns identified in this study can help to choose suitable shoulder exercises dependent on the training objective.