Internal rotation in the 3rd position as a candidate marker for multi-year shoulder ROM monitoring in collegiate pitchers: a 4-year individual follow-up of six clinical measures

Background This study aimed to characterize four-year longitudinal changes and inter-individual variability in shoulder range of motion (ROM) in collegiate baseball pitchers, and to identify which of six commonly used clinical ROM measures shows the most consistent longitudinal change. Methods This longitudinal observational study included 10 collegiate baseball pitchers who underwent preseason medical check-ups annually from the first academic year through the preseason of the fourth academic year. Shoulder ROM was assessed using six commonly used clinical measures of external rotation, internal rotation, and posterior shoulder tightness, and throwing–non-throwing side differences were calculated. Linear mixed models (LMM) using all four annual time points were the primary analysis; paired t-tests with Holm adjustment (Year 1 vs Years 2, 3, and 4) served as a confirmatory analysis. Robustness was assessed with three sensitivity analyses. Results After Holm adjustment, only internal rotation in the 3rd position (IR3) showed a significant decline from Year 1 to Year 4, whereas no other ROM measure changed significantly. Mixed-model analyses across all four time points similarly indicated a significant negative longitudinal trend in IR3 (− 3.8°/year, 95% CI − 6.6 to − 1.0; p = 0.009), with no meaningful trends for other measures. The IR3 finding was consistent across all sensitivity analyses, and the decline was selectively driven by the throwing side, whereas the non-throwing side remained essentially unchanged. Individual trajectories varied substantially; most pitchers showed IR3 loss over time, while some remained relatively stable. Conclusions Long-term shoulder ROM changes among collegiate pitchers showed marked inter-individual variability. IR3 was the only measure demonstrating robust deterioration across the primary, confirmatory, and sensitivity analyses, suggesting that IR3 may be a candidate marker for longitudinal monitoring of shoulder mobility during the collegiate competitive period.