Abstract: During isokinetic shoulder elevation in the coronal and sagittal
planes, the centre of rotation of the glenohumeral joint was displaced 8-cm
vertically relative to the centre of rotation of the dynamometer's actuator
arm. It was suggested that in order to account for this displacement, the
recorded maximum moment values should be reduced by 12.5%. displacement of the
glenohumeral centre of rotation (DGCR) during isokinetic shoulder elevation in
the scapular plane and to conduct an error analysis of the dynamometer's moment
recordings. The DGCR was assessed in twenty healthy volunteers, during
isokinetic concentric elevation of the left shoulder, in the scapular plane,
using a two-dimension motion analysis system. Measurements were performed at
30, 60 and 120°·s^{-1},
between 30--90° of shoulder elevation and were
analysed every 12°. The glenohumeral centre of
rotation was superomedially displaced relative to the centre of rotation of the
actuator arm, throughout shoulder elevation (P < 0.001). The
effect of isokinetic velocity on the DGCR was not significant. The DGCR
resulted also in changes of humeral lever arm orientation and length relative
to the pre-set orientation and length of lever arm. As a result of these
changes, dynamometer's recordings underestimated corrected angle-based maximum
moments by ≤ 6.2%. isokinetic elevation of the shoulder
in the scapular plane was probably attributed to normal kinematics of shoulder
elevation that requires synchronous function of both the scapulothoracic and
glenohumeral joints. The cutaneous markers and the 2-D kinematic analysis
system used for the assessment of a 3-D shoulder motion may effect the
precision in detecting movements of the shoulder under the skin. The present
findings are also limited to the position, stabilisation method and range of
motion tested.
Keywords: Isokinetic, shoulder elevation, centre of rotation, alignment, scapular plane
