Isokinetic dynamometry in assessment of external and internal axial rotation strength of the shoulder: Comparison of two positions

Abstract

Background: Measuring isokinetic strength of the shoulder complex is potentially an important clinical tool in both diagnosis and management of injury and pathology. However, a clinically relevant position is yet to be established. Objectives: To establish an appropriate and repeatable protocol to evaluate the functional strength of both internal and external rotators of the glenohumeral joint to enable assessment of clinical injury management and training related developments in upper limb strength. Methods: A population cross-sectional study of shoulder internal and external rotational strengths of 17 normal, healthy volunteers (11 males, 6 females) aged 21 to.45 years were measured both isokinetically and isometrically. Two test positions: seated and supine, were compared by way of reliability and repeatability analyses. Humeral rotation was performed at 45° of abduction in the scapular plane seated, and at 90° of abduction in the supine position. Results: Throughout concentric testing, when the population was considered as a whole the left shoulder data appeared more repeatable than the right shoulder. This however, was not evident when the study population was divided into single sex groupings. Equally, whilst the repeatability trend of sitting vs. supine position was skewed towards the former, more evident in the left shoulder, this was less apparent when sexes were analysed separately. All comparative measures were statistically insignificant. Conclusion: The findings of this study suggest that measurements of isokinetic shoulder rotation strength are highly prone to both joint specific and non-specific errors.