HYPOTHESIS AND/OR BACKGROUND: We aimed to investigate the contributions of grip, pronation, and pinch in stabilization of the medial elbow joint space; examine their relationship with muscle strength; and assess the effect of stabilization on the medial elbow joint space in baseball pitchers. METHODS: In this controlled laboratory study, we measured the medial elbow joint space using ultrasound during unloading, loading, and loading with grip, pronation, and pinch conditions. To evaluate changes in the medial elbow joint space as a result of various conditions, one-way repeated-measures analysis of variance (ANOVA) and post hoc analysis for multiple comparisons were performed. To investigate whether strong or weak muscle strength improved the medial elbow joint space during the loaded condition, Pearson's correlation analysis was performed. Finally, a post-hoc power analysis was performed. RESULTS: We enrolled 121 pitchers. The medial elbow joint spaces in the loaded, loaded with full grip, and loaded with full pinch conditions were significantly larger than those in the unloaded condition. The medial elbow joint spaces in the loaded with full grip, loaded with full pronation, and loaded with full palmar pinch conditions were significantly smaller than those in the loaded condition. A post hoc power analysis showed that the power of the one-way repeated-measures ANOVA was 100%. The strengths of the full grip and palmar pinch were significantly correlated with a reduced gap distance of the medial elbow joint space (both P < .001). DISCUSSION AND/OR CONCLUSION: In high school baseball pitchers, pronation and palmar pinch contraction significantly improved the gap distance of the medial elbow joint space in the loaded condition and during grip contraction. Moreover, the grip and palmar pinch strengths were significantly correlated with stabilizing effects on the medial elbow joint space.