Electromyographic analysis of the glenohumeral muscles during a baseball rehabilitation program

Abstract

Many exercises are used to strengthen the glenohu meral muscles, but there have been limited studies to evaluate the exercises. Thus, the purpose of this study was to decide how the muscles responsible for humeral motion can best be exercised in a rehabilitation program for the throwing athlete. Dynamic, fine wire, intramus cular electromyography was carried out in 15 normal male volunteers performing 17 shoulder exercises de rived from a shoulder rehabilitation program used by professional baseball clubs. The four rotator cuff mus cles were studied, as well as other positioners of the humerus, including the pectoralis major, latissimus dorsi, and three portions of the deltoid. The electro myographic activity was synchronized with cinematog raphy and averaged over 30° arcs of motion. An exer cise was considered to be a significant challenge for a muscle if it generated at least 50% of its predetermined maximum contraction over three consecutive arcs (i.e., a 90° range). Four exercises were consistently found to be among the most challenging exercises for every muscle. These shoulder exercises consisted of 1) ele vation in the scapular plane with thumbs down, 2) flexion, 3) horizontal abduction with arms externally rotated, and 4) press-up. This study documents that the minimum for an effective and succinct rehabilitation protocol for the glenohumeral muscles would include these exercises.