Lateral epicondylalgia/epicondylitis is generally seen in individuals who live an athletic lifestyle such as tennis players or baseball players. It is pain at the outside of the elbow and forearm. It affects the extensor bundle of the elbow (predominantly the extensor carpi radialis brevis). The primary reason that an individual may get pain in this area is from repetitive movements. But what would cause this muscle to be over worked?
A study by Lucado et a. showed that reduced lower trapezius muscle strength and endurance will change the movements of the elbow of tennis players. Another study showed that increased pain and activation of the upper trapezius caused an increase in the extensor bundle muscle activation at the elbow.
A study by Day et al. wanted to compare scapular muscular strength, endurance, and change in thickness of individuals with and without lateral epicondylalgia. They assessed the middle trapezius, lower trapezius, and serratus anterior muscles. They found there were significant differences for middle trapezius, serratus anterior, and lower trapezius muscle strength and endurance and a significant change in serratus anterior muscle thickness.
So the moral of the story is that if someone has lateral epicondylalgia then muscles of the shoulder should be checked out as well. If those muscles cannot control and stabilize the shoulder blade then the muscles of the arm have to work just a little bit harder.
Day JM, Bush H, Nitz AJ, Uhl TL. Scapular muscle performance in individuals with lateral epicondylalgia. J Orthop Sports Phys Ther. May 2015; 45(5): 414-424.