EMG-aktivering av rotatorcuffen vid olika muskelstärkande aktiviteter - En biomekanisk studie.

Abstract: Introduction Both M. Supraspinatus and M. Infraspinatus of the rotator cuff play a role in stabilizing the shoulder during movement. When rehabilitating shoulders after injury a wide range of tools are used to strengthen the shoulder, often including a pulley system or TheraBand. According to evidence, no tool does however stand out as the most optimal one to use. Purpose The purpose of this study was to compare the electromyographic (EMG) activity in m. infraspinatus and m. supraspinatus during two different isometric muscle-strengthening exercises for external rotation. Research questions What is the difference in peak EMG amplitude in m. supraspinatus while using TheraBand versus pulley system in isometric external rotation? What is the difference in peak EMG amplitude in m. infraspinatus while using TheraBand versus pulley system in isometric external rotation? Is there any correlation between degree of external rotation and peak EMG amplitude during loaded isometric external rotation? Materials and Methods 10 healthy participants without musculoskeletal shoulder problems were tested using EMG surface electrodes. Each participant was instructed to perform a maximal voluntary isometric contraction (MVIC), which granted a maximal EMG value for the assessed muscles. The participants were then ordered to perform isometric holds in 30° respectively 60° external rotation, using both a TheraBand and a pulley system. The raw EMG values were digitally filtered and compared to the MVIC EMG value for reference. Results Significant difference was observed between the two exercises in 30° external rotation, where the pulley system provided a significantly higher muscle activity than TheraBand in m.infraspinatus. Additionally, significant increases of EMG-activity were noted in both muscles for both exercises while comparing 60° of external rotation with 30°. Conclusion The study found it difficult to answer the question posed due to difficulties standardizing the TheraBand resistance in accordance with the pulley system. The pulley system can be adjusted to a fixed resistance while the TheraBand increases the resistance as it elongates.