Elasticity of baseball players’ posterior shoulder capsule during internal rotation stretching at 30 degrees of scaption

Previous cadaveric studies have identified effective stretching positions for the posterior shoulder capsules; however, it is unknown whether these stretching positions are also effective in overhead athletes. This study aimed to investigate whether passive tension was generated in the posterior shoulder capsules in baseball players during stretching positions identified in previous cadaveric studies. Fifteen male baseball players without prior shoulder injuries or surgeries participated in this study. We measured the shear moduli of the middle and inferior posterior capsules of the dominant shoulder in the resting (neutral shoulder internal/external rotation at 30 degrees of flexion) and stretching (maximal shoulder internal rotation at 30 degrees of scapular plane elevation (scaption)) positions using ultrasound shear wave elastography. The shear moduli of the middle posterior capsule were significantly higher in the stretching position than in the resting position (resting vs stretching: 20.9 vs 34.6 kPa, P < .001); however, there was no significant difference in the shear moduli between both positions in the inferior posterior capsule (22.3 vs 29.5 kPa, P = .120). Our results revealed that a large amount of passive tension is generated in the middle posterior capsule during shoulder internal rotation stretching at 30 degrees of scaption in overhead athletes.