Shoulder Muscles: A Case Study

Chapter I The Problem and Its Scope
Introduction
The shoulder contains complicated groups of muscles, tendons, ligaments, and bursae all involved in humeral and scapular kinematics (Terry & Chopp, 2000). Regular use of the arms can result in fatigue of shoulder musculature, which could lead to altered scapular kinematics during humeral elevation (Tsai, McClure, & Karduna, 2003). These changes in scapular kinematics can potentially lead to shoulder problems such as impingement syndrome, rotator cuff tears, and glenohumeral instability (Ebaugh, McClure, & Karduna, 2006). It is important to investigate the effects of fatigue on individual shoulder muscles to further understand their role in shoulder injuries. This could help prevent future shoulder injuries …show more content…
In particular, the infraspinatus is involved in external rotation and stabilization of the humerus as a humeral head depressor by pulling the humerus towards the glenoid fossa of the scapula (Ngomo, Mercier, & Roy, 2013). There was an increase in superior translation of the humeral head while using a nerve block to cause dysfunction of the infraspinatus and supraspinatus. This increase is also often seen in individuals experiencing shoulder impingement syndrome (San Juan, Kosek, & Karduna, 2013). Reddy, Mohr, Pink, & Jobe (2000) found that the infraspinatus showed a significant decrease in electromyographic activity during humeral elevation when comparing subjects with shoulder impingement syndrome to a control group. This suggests that the infraspinatus is an essential muscle to investigate regarding alterations in activity due to fatigue. A good amount of studies have examined infraspinatus functions and fatigue peripherally (D. Ebaugh et al., 2006; Reddy et al., 2000; Tsai et al., 2003), but none have examined the effects of fatigue on the infraspinatus