Author(s): REN, X., Institution: SHANGHAI RESEARCH INSTITUTE OF SPORTS SCIENCE, Country: CHINA, Abstract-ID: 1363

INTRODUCTION:
To examine longitudinal changes in shoulder eccentric–concentric strength balance during rehabilitation following anterior shoulder instability and to evaluate the clinical utility of the functional deceleration ratio (ECC ER/CON IR) during phased return-to-sport progression.
METHODS:
A 22-year-old professional beach volleyball athlete with traumatic anterior instability and confirmed Bankart lesion underwent a structured, phase-based rehabilitation and progressive sport-specific loading program beginning March 2023.Training volume increased systematically across three phases from controlled overhead exposure (0–20 hits/week) to unrestricted overhead training (>50 hits/week).Isokinetic testing (ISOMED 2000) was performed in a seated abduction–external rotation position at 60°·s⁻¹. Peak torque of eccentric external rotation (ECC ER) and concentric internal rotation (CON IR) was assessed on April 13, May 8, and June 14, 2023.The functional deceleration ratio (ECC ER/CON IR) was calculated to reflect posterior rotator cuff capacity to decelerate internal rotation torque during overhead motion. Ratios ≥1.0 have been reported in healthy overhead athletes and are considered indicative of adequate dynamic shoulder stability.
RESULTS:
Initial testing showed ECC ER 88 Nm and CON IR 81 Nm (ratio = 1.09), consistent with values reported in healthy overhead athletes despite clinical symptoms.During increased sport-specific loading, absolute torque values temporarily decreased (65 vs. 64 Nm; ratio = 1.02).At final assessment, strength values re-balanced symmetrically (70 vs. 70 Nm; ratio = 1.00), coinciding with successful progression to higher-volume overhead training.Absolute torque values fluctuated across phases, whereas the functional ratio remained stable and clinically interpretable.
CONCLUSION:
Shoulder rotator strength demonstrates non-linear adaptations during rehabilitation following Bankart lesion.The functional deceleration ratio provided meaningful insight into dynamic shoulder stability that was not fully captured by absolute strength values alone.Monitoring eccentric–concentric strength balance may support individualized load management and evidence-informed return-to-sport decision-making in overhead athletes.