An Analysis of In Vivo Hip Kinematics in Elite Baseball Batters Using a Markerless Motion-Capture System

PURPOSE: The aim of this study was to investigate the kinematics of the asymptomatic baseball batter’s hips by comparing passive range of motion (PROM) and real-time active hip range of motion (AROM) and determine whether differences in ROM exist between lead and trail hips. METHODS: Parameters of passive hip ROM were obtained using a goniometer and physical examination standards. Active hip ROM during batting swings was captured with the Dynamic Athletic Research Institute’s markerless motion-capture system. RESULTS: Twenty-nine elite-level baseball players were recruited for participation. Comparison of lead and trail hips showed no significant differences in PROM. Statistically significant differences in AROM were found between lead and trail legs with large effect sizes for flexion (mean difference [MD°], 11.22), extension (MD°, 30.30), abduction (MD°, 6.24), adduction (MD°, 18.63), external rotation (MD°, 14.87) and total arc of rotation (MD°, 17.17) (P < .001 for all). External rotation in the lead hip approached maximum passive endpoint during early phases of the swing, whereas trail hip extension reached maximum passive endpoint during follow-through. CONCLUSION: There is a significant difference in the AROM of the lead and trail hips during the batting swing, with active extension in the trail hip, active external rotation of the lead hip, and total arc of rotation of the lead hip nearing their respective passive endpoints and suggesting a potential for bony interaction in the hips of baseball batters. LEVEL OF EVIDENCE: Level 3, Cross-Sectional Study.