Effects of different arm external loads on the scapulo-humeral rhythm

Abstract

Objective. To investigate the effects of the magnitude of the external load, applied on the hand, on the orientation of the shoulder girdle (scapulo-humeral rhythm). Design. Thirty subjects performed both arms' elevation in three planes of elevation: sagittal (anteflexion), frontal (abduction), and scapular (scaption). Measurements were performed against five levels of external load (0–4 kg), on each plane of elevation. Background. Some controversy exists whether additional load influences the SHR. Moreover, no data are available on the SHR during arm abduction and anteflexion. Methods. The SHR was recorded by means of a six degree of freedom electromagnetic tracking device. Results. The external load applied on the hand affects scapular three-dimensional position: scapular protraction is particularly affected on abduction and scaption; scapular latero-rotation on anteflexion and abduction; and scapular spinal tilt on anteflexion. Conclusions. The magnitude of the external load, applied on the hand, influences the scapular position and the scapulo-humeral rhythm, particularly on abduction. Those effects are visible on scapular latero-rotation and spinal tilt, during anteflexion, and on scapular protraction during scaption. Additionally, the initial position of the shoulder girdle seems to play an important role on the definition of the individual SHR pattern. Relevance This study can provide a basis for evaluation of shoulder pathology associated with abnormal scapular kinematics.