Like many other parts of the anatomy, the rhomboid muscles get their name from the Latin word describing their shape, with said shape here being a rhombus; a diamond. Actually a pair of muscles—the rhomboid major and rhomboid minor—they act collectively to retract and lower the scapula (otherwise known as the shoulder blade) medially towards the spine while also fixing the scapula to the thoracic wall. This action is possible through their attachment (or 'origin') from the C7 through T5 spinal vertebrae, collectively, and inserting upon the medial border of the scapula. Lying deep to and working in conjunction with other muscle groups collectively known as scapular muscles (such as the trapezius muscles and serratus anterior), the rhomboids are important from a baseball perspective due to their ability to stabilize the shoulder joint and provide postural support, especially while throwing.
Unfortunately for Atlanta Braves catcher Evan Gattis, the importance of the rhomboids recently became a little more pronounced and a little more painful, as he suffered spasms of the right rhomboid in Friday's game against the Philadelphia Phillies while swinging and missing on a changeup. While the injury will provide its share of pain and discomfort, it will not be debilitating and should dissipate with conventional treatment methods, including anti-inflammatory medication and perhaps a muscle relaxant (depending upon severity), ice/heat treatment, as well as massage and stretching of the affected area.
With regards to baseball activities, the rhomboid spasm is a mixed bag as to how much it will potentially affect Gattis' performance. Given the injury is on the side of his throwing arm, it will be the complexities of the scapulohumeral rhythm (SHR) in overhead throwing and the importance of the scapular muscles in achieving the correct position and motion of the shoulder joint in throwing that will be at greatest risk as Gattis recovers. The scapula displays motions in three planes and translations in two directions and rarely moves in only one of these directions or translations during the throwing motion, lending importance to the scapular muscles and their activations; while research has shown the other two scapular muscles to contribute the most to scapular mobility and stability, the rhomboids still play an important secondary role.
A recent electromyographic study of the rhomboids in pitching showed that they are most active in the deceleration phase and second most active in the acceleration phase of throwing, underlining the importance of the rhomboids in maintaining the health of the shoulder joint and proper biomechanical processes of the throwing motion. With Gattis being a catcher, the rhomboids are at greater risk of injury re-aggravation, due to the necessity for catchers to quickly and powerfully throw from less than optimal anatomical positions during stolen base attempts. In the less than two seconds afforded a catcher to get off a good throw, the role of the rhomboids to medially rotate and depress the scapula in the cocking phase and then assist in the deceleration of the shoulder joint upon release of the throw is intensified. With the discomfort of the injury, Gattis' ability to snap off a quick, strong, and accurate throw could also be limited due to pain and decreased range of motion of the scapula arising from the rhomboid injury.
Given Gattis' plus tool being his offense, with his defensive skills a tad dubious at this point in his career, it is somewhat of a relief that the effects of a rhomboid spasm or strain on swinging a bat—at least in his case—in minimized. Since the offending injury is on the right side, Gattis being a righthanded hitter will have almost a protective effect on recovering from the spasms, as the right arm and shoulder are more or less pushed through the hitting plane by the pectoralis major, serratus anterior, and deltoid muscles on the right side, with the left sided pulling the bat through the plane, concomitantly; the right rhomboids, for the most part, are just along for the ride in hitting as a righty.
And while it is a minor player in the event, the rhomboids do provide the aforementioned postural support while running, allowing for proper arm swing. With Gattis, the necessity for optimal arm swing when running is shall we say minimal, and shouldn't greatly affect this aspect of his overall game.
While there is no such thing as a minor injury, it appears that Gattis should recover from his without many hassles and in quick form. While the complexity of the scapula and its underlying role in the health of the shoulder joint merits additional caution in his rehabilitation, Gattis should not experience any lingering effects of the rhomboid spasms. Additional care will be taken to ensure that this issue will not evolve into larger ones, in particular, scapular dyskinesis, a loss of normal resting scapular position arising from weakness or injury of the scapular muscles, but with proper treatment and rest, El Oso Blanco will continue to swing it with ease.
References: Dines, J. S. (2012). Sports medicine of baseball. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.