Shoulder proprioception is associated with humeral torsion in adolescent baseball players

Objectives To determine the relationship between the amount of humeral torsion and a measure of active proprioception in adolescent male throwing athletes. Design Cross-sectional laboratory study with uninjured subjects. Setting University of Sydney and NSW Institute of Sport. Participants Participants were 16 adolescent male baseball players (15.0–18.1 years old, SD=16.3) holding baseball scholarships at the NSW Institute of Sport. Main outcome measures The main outcome measures, active proprioception (shoulder rotation, in 90° of arm abduction moving towards external rotation, using the Active Movement Extent Discriminating Apparatus) and humeral torsion (using an ultrasound-assisted method), were measured bilaterally. Results A strong ( r =0.88) and significant ( p =0.001) correlation was found between increasing humeral retrotorsion and better active proprioceptive acuity in the non-dominant arm, while the relation was weaker ( r =0.41) and did not reach statistical significance ( p =0.120) for the dominant arm. Conclusions A cognitive processing capacity model, which suggests that greater humeral retrotorsion reduces neural processing requirements, has been proposed to explain the direct relationship between proprioceptive acuity and humeral retrotorsion.