The relationship between shoulder range of motion and elbow stress in college pitchers

Abstract

Hypothesis: College pitchers with increased external rotation gain (ERG) produce increased medial elbow torque (elbow stress) whereas those with reduced total rotational range of motion (ROM) have reduced medial elbow torque during pitching.

Methods: Pitchers were recruited from 3 college baseball teams. Players with prior injury or on pitching restrictions because of pain were excluded. Players were evaluated within 2 weeks before their first game of the season. Pitchers completed an intake survey, and shoulder and arm measurements were taken. Pitchers were fitted with a baseball sleeve that included a sensor at the medial elbow. The sensor calculated elbow torque, arm speed, arm slot, and shoulder rotation for each pitch, while a radar gun measured peak ball velocity. After adequate warm-up, pitchers threw 5 fastballs in a standardized manner off the mound at game-speed effort. The primary outcome evaluated the relationship between shoulder ROM and medial elbow torque. Additional outcomes evaluated pitcher characteristics and demographic characteristics in the context of shoulder ROM.

Results: Twenty-eight pitchers were included in the preseason analysis. The average age and playing experience were 20.1 years (standard deviation [SD], 1.3 years) and 15.3 years (SD, 1.8 years), respectively, with 2.5 years (SD, 1.2 years) playing at collegiate level. The dominant shoulder showed decreased internal rotation and increased external rotation (ER) relative to the nondominant side (P < .001). The average glenohumeral internal rotation deficit and ERG were 11.3° (SD, 9.87°) and 5.71° (SD, 8.8°), respectively. ERG ≥ 5° was a significant predictor of elbow stress during pitching (47.4 Nm [SD, 0.7 Nm] vs. 45.1 Nm [SD, 0.6 Nm], P = .014). Univariate associations showed that each additional degree of ER resulted in increased elbow torque (β estimate, 0.35 ± 0.06 Nm; P = .003). Conversely, decreased medial elbow torque was found in pitchers with reduced shoulder ROM (glenohumeral internal rotation deficit ≥ 20°: 43.5 Nm [SD, 1.1 Nm] vs. 46.6 Nm [SD, 0.5 Nm], P = .011; loss of total rotational ROM ≥ 5°: 43.6 Nm [SD, 1.1 Nm] vs. 46.6 Nm [SD, 0.5 Nm], P = .013) and in those with greater arm length (P < .05).

Conclusions: College pitchers with increased ER produce greater medial elbow torque during the pitching movement. Each degree of increased ER was found to correlate with increased elbow torque and ball velocity. On the contrary, arm length and reduced shoulder ROM were associated with reduced medial elbow torque. This study suggests that increased ER in pitchers is associated with greater elbow stress during pitching.

Keywords: GIRD; Tommy John; UCL; elbow; glenohumeral internal rotation deficit; injury; pitching; ulnar collateral ligament.