This study aimed to investigate differences in electromyographic (EMG) muscle activity and scapular kinematics during elevation in the scapular plane between healthy controls, participants with multidirectional shoulder laxity (MDL), and patients with multidirectional shoulder instability (MDI) who are diagnosed with hypermobile Ehlers‐Danlos syndrome (hEDS) or Hypermobility Spectrum Disorder (HSD). Twenty‐seven women with hEDS/HSD and MDI, 27 female healthy control subjects, and 28 female subjects with MDL participated in this study. Scapular 3D kinematic data were obtained using 8 Oqus Qualisys cameras.

Simultaneously, surface electromyography (EMG) was used to measure the upper, middle, and lower trapezius muscle activity, infraspinatus, latissimus dorsi, serratus anterior, posterior deltoid, and pectoralis major during arm elevation in the scapular plane. Group differences were assessed using statistical parametric mapping. Regarding scapular kinematics, the significantly less upward rotation was observed in hEDS/HSD patients with MDI than healthy controls and MDL subjects. Significantly less posterior tilt was seen in hEDS/HSD patients compared to MDL subjects. Furthermore, significantly higher EMG activity of the infraspinatus, middle trapezius, and posterior deltoid was found in hEDS/HSD patients with MDI.

In conclusion, hEDS/HSD patients with MDI demonstrate altered scapular kinematics and increased EMG muscle activity compared to subjects without MDI. These findings could be a stepping stone for future research regarding treatment strategies in patients belonging to the hypermobility spectrum.