Background The glenohumeral joint poses one of the biggest challenges to orthopaedic surgeons when compared with other joints within the human body. Until recently the accurate measurement of contact loads acting in the glenohumeral joint have been difficult to calculate and define. Now, contact forces and moments are measured in vivo using telemeterized shoulder implants. Methods An in vitro testing rig that represents 6° of freedom, full musculature, and two instrumented prosthetic heads was designed in an attempt to replicate the in vivo motion and forces in the glenohumeral joint. Multiple tests were applied to the shoulder complex to investigate forces generated and the effects on joint mechanics. These tests were based on activities of daily living. Results The testing rig showed high repeatability in all test directions, with readings showing R 2 values of more than 0.98. There also was high conformity between the test results and previously published in vivo data. Conclusion The testing rig provided an accurate test platform with highly repeatable results. This is a significant development from the in vivo testing method. Using this testing rig, it will be possible to investigate the biomechanics of the glenohumeral joint further and investigate destructive forces, fixation methods, and injuries. Recommendations can then be made regarding treatment of different fractures and for different bone properties and populations.