Relationship Differences in Pre-season Isometric Shoulder Strength, Humeral Torsion and Shoulder Range of Motion in Collegiate Baseball Players (218)
Authors: Arnold Amanda , Choate W. Stephen 
Published: October 2021

Objectives: Muscle strength, humeral torsion (HT) and shoulder range of motion (ROM) have been linked to throwing performance and injury risk in baseball players. Research suggests that players who demonstrate an isometric shoulder external rotation (ER)/internal rotation (IR) strength ratio of <0.75 are at a higher risk for developing a throwing-related upper extremity injury. While the relationships between HT and shoulder ROM have been examined in the literature, few studies have examined the potential relationships between these variables and isometric shoulder strength. The purpose of this study was to examine the relationships between isometric shoulder strength, HT and shoulder ROM at the start of each baseball season in a cohort of healthy junior college baseball players. Methods: Ninety-two healthy junior college baseball players (mean age=19.9±0.8 years) were prospectively assessed at the start of 2 consecutive spring seasons. Variables measured included HT, shoulder ROM and isometric shoulder strength. Both the dominant (D) and non-dominant (ND) shoulders of each player were assessed throughout the study. Chi square tests and bivariate Pearson correlation coefficients were calculated to examine between group differences and the relationships between variables. Statistical significance was set a priori at α=0.05. Results: 33.7% of junior college players demonstrated a D shoulder ER/IR strength ratio of <0.75 at the start of baseball season. Pitchers and position players demonstrated no significant differences in D shoulder ER/IR strength ratios at the start of the season (P=.40). Additionally, moderate positive relationships were observed between D HT and D IR ROM (r=0.35; P=.001) as well as D horizontal adduction (HA) ROM (r=0.43; P<.001). A moderate relationship was also observed between ND HT and ND IR ROM (r=0.56, P<.001), however ND ER and HA ROM demonstrated weaker relationships respectively (ER: r=-0.27; P=.01; HA: r=0.26; P=.01). Inverse relationships were observed between HT and ER strength in both the D and ND shoulders (D: r=-0.27, P=.01; ND: r=-0.28, P=.007). Internal rotation ROM was also inversely correlated with ER strength (r=-0.29, P=0.005) and ER/IR strength ratios (r=-0.31, P=.003), but only in the D shoulder. No significant correlations were observed between ROM and strength in the ND shoulder. Conclusions: One third of the junior college baseball players in this study began the season with marked deficits in D shoulder strength, irrespective of their position. We then examined the relationships between HT, shoulder ROM and isometric shoulder strength and confirmed the previously established correlation between HT and shoulder ROM. Moreover, there appeared to be inverse relationships between HT and ER strength in both the D and ND shoulders as well as IR ROM and ER strength in the D shoulder. This study emphasizes the importance of pre-season rotator cuff strength training, with an emphasis on improving ER strength, to potentially aid in the prevention of throwing-related upper extremity injuries in collegiate baseball players. Humeral torsion and shoulder ROM may influence isometric shoulder strength, however more research is needed to better understand these relationships in the throwing shoulder.