Investigation of the Neuromuscular Control of the Shoulder When Performing Concurrent Upper Extremity Tasks

Abstract

<p>The purpose of the thesis was to evaluate the neuromuscular control of shoulder muscles when performing concurrent shoulder and hand or elbow efforts in healthy and injured individuals. Of particular interest was the response of the supraspinatus and infraspinatus muscles to performing an additional hand task, such as gripping, while also performing different shoulder actions. Two studies were undertaken to provide the necessary groundwork for the subsequent two studies of this thesis. The first study investigated whether changes to shoulder muscle activity previously seen with gripping where the result of the novelty of using feedback to regulate grip force. This study found that changes in shoulder muscle activity with gripping are not diminished with repetition. The second study provided an improved method of normalizing electromyograms from dynamic contractions and was used in the subsequent studies of this thesis. Studies 3 and 4 of this thesis examined the response of shoulder muscles in healthy individuals during static sub-maximal efforts and maximal dynamic efforts in flexion and scapular planes with neutral and supinated forearm postures. Three conditions were tested in both studies: (i) no additional load, (ii) gripping to 30% of maximum and (iii) contracting the biceps to 30% of maximum. A prevailing theme found during sub-maximal contractions was individuality in neuromuscular recruitment strategies and precluded any significant effects of gripping or biceps contractions. During dynamic contractions, concurrent shoulder efforts with gripping and biceps contractions was found to significantly decrease deltoid, supraspinatus and infraspinatus muscle forces during flexion with supinated forearm posture. This thesis provided a thorough examination of shoulder electromyography in healthy individuals, improving our understanding of the neuromuscular control of the shoulder musculature. A common theme of this thesis was the individuality of neuromuscular strategies of the shoulder.</p>