Effect of sitting posture on 3-dimensional scapular kinematics measured by skin-mounted electromagnetic tracking sensors

Objective: To determine the effect of trunk sitting posture on scapular kinematics during humeral elevation by using skin-mounted electromagnetic tracking sensors. Design: Repeated-measures design contrasting scapular kinematics in 2 different sitting postures. Setting: A biomechanics laboratory in Hong Kong with a real-time, 3-dimensional electromagnetic tracking device for measuring movements of the scapula. Participants: A sample of 16 healthy adults (12 women, 4 men; age, 21.6 +/- 3.92y) with full, pain-free shoulder range of motion and no history of shoulder pathology. Interventions: Not applicable. Main Outcome Measures: Movements of the scapula were measured while each subject performed humeral elevation in an upright seated position and a slouched seated position. Results: In both postures, posterior tip, lateral and upward rotation of the scapula, and lateral rotation of the humerus were observed during humeral elevation. When the slouched posture was adopted, there were significant decreases in the posterior tip and lateral rotation of the scapula, but there was no significant change in the magnitude of the upward rotation of the scapula. Conclusion: Increased thoracic kyphosis significantly alters the kinematics of the scapula during humeral elevation.