Aim: To describe accurately the contributions of glenohumeral (GH) and scapulothoracic (ST) joints in shoulder movements in normal male adult subjects, aged 20–30 years.

Methods: We recorded data with a Polhemus magnetic tracking device (Kaiser Aerospace and Electronics Co., Vermont). Receivers were taped on landmarks, over the sternum, scapula and humerus. The movements that were studied were elevation in the sagittal plane, abduction in the scapular plane and lowering the arm from these positions. We collected data from 26 male subjects (52 shoulders), aged 20–30 years, with no history of shoulder problems. Repeatability data were obtained in 16 subjects.

The data can be expressed in a number of ways, including plotting the ratio of GH/ST movement versus overall shoulder movement. Polynomial equations to fit these curves describe movement patterns. We have developed software to calculate cumulative averaging of data.

Results: Both GH and ST movements contribute to shoulder movement throughout the ranges studied. Although the shapes of the movement curves were fairly consistent, there were some non-conforming curves and variations. As the arm is abducted the mean ratio of GH/ST movement increases to approximately 3/1. Adduction produces curves that nearly mirror image the abduction curves. Flexion and extension curves tend to be flatter with a mean GH/ST ratio of 2–3/1, throughout the range. The reproducibility data shows satisfactory fits to initial curves.

Conclusions: We have developed a method to describe shoulder movement that provides new information regarding normal shoulder movements. This method can be applied to study patients with shoulder disorders.