A force-couple relationship is the act of muscles or muscle groups moving together, in a synergistic manner, to produce movement around a joint.
When most people discuss movement and muscle, they tend to believe that a single muscle pulling on a bone creates movement. However, we now know that movement is created by the recruitment of muscle groups, which in turn creates a force-couple, utilizing various lines of pull and forces to create that movement. They can be agonist-antagonist pairs or synergistic pairs.
In pitching we will notice many force-couple relationships, such as the deltoid rotator cuff force-couple. While this force-couple relationship is not unique to pitching (duh), it is important as the 2 muscle groups work together to provide movement and stabilization.
For instance, while the Anterior Deltoid concentrically accelerates shoulder flexion and internal rotation, the Teres Minor eccentrically decelerates shoulder internal rotation. The deltoid and rotator cuff force couple allows for movement of the humerus, while stabilizing the humerus at the same time, to prevent migration of the humeral head from the glenoid fossa during most phases of throwing.
This is why pitchers need to work on rotator cuff strength, although we do not want to work to fatigue. There are plenty of other examples that can be used to explain force-couple relationships during pitching, but I’ll only list a few more, such as:
- Serratus anterior and Pectoralis minor during Scapular Protraction (during ball release)
- Serratus anterior, upper and lower trapezius, rhomboids, pectoralis minor and levator scapulae during Scapular Upward Rotation
- Anterior and middle deltoid, Supraspinatus (synergist), as well as Latissimus dorsi, pectoralis major, teres major, coracobrachialis, long head of triceps, infraspinatus, teres minor and subscapularis (antagonists) during Shoulder Abduction.
Here’s a good video that explains the force-couple relationship theory.
If you have any questions (or comments) please ask in the comments section below.