Effects of posture,movement and hand load on shoulder muscle activity |
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| Authors: | Nicholas T Antony Peter J Keir |
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| Institution: | 1. Department of Kinesiology, McMaster University, 1280 Main St W, Hamilton, ON, Canada L8S 4K1;2. School of Kinesiology and Health Science, York University, 4700 Keele Street, Toronto, ON, Canada M3J 1P3;1. Musculoskeletal Science Research Group, Institute of Translational Medicine, University of Liverpool, Liverpool, UK;2. School of Health Sciences (Sport and Exercise Science), Liverpool Hope University, Liverpool, UK;3. Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, UK;4. Department of Medical Physics and Clinical Engineering, Royal Liverpool University Hospital, Liverpool, UK;5. Department of Physics, University of Liverpool, Liverpool, UK;1. Department of Exercise Science and Physical Education, Montclair State University, 1 Normal Avenue, Montclair, NJ 07043, United States;2. Oregon Neurosurgery, 3355 Riverbend Drive, Suite 400, Springfield, OR 97477, United States;3. Department of Human Physiology, University of Oregon, 1240, Eugene, OR 97403, United States;1. Department of Orthopaedic Surgery, Tohoku University School of Medicine, Sendai, Japan;2. Division of Cyclotron Nuclear Medicine, Cyclotron and Radioisotope Center, Tohoku University, Sendai, Japan;1. School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Taipei, Taiwan;2. Physical Therapy Center, National Taiwan University Hospital, Taipei, Taiwan |
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| Abstract: | The influence of external factors such as arm posture, hand loading and dynamic exertion on shoulder muscle activity is needed to provide insight into the relationship between internal and external loading of the shoulder joint. Surface electromyography was collected from 8 upper extremity muscles on 16 participants who performed isometric and dynamic shoulder exertions in three shoulder planes (flexion, mid-abduction and abduction) covering four shoulder elevation angles (30°, 60°, 90° and 120°). Shoulder exertions were performed under three hand load conditions: no load, holding a 0.5 kg load and 30% grip. It was found that adding a 0.5 kg load to the hand increased shoulder muscle activity by 4% maximum voluntary excitation (MVE), across all postures and velocities. Performing a simultaneous shoulder exertion and hand grip led to posture specific redistribution of shoulder muscle activity that was consistent for both isometric and dynamic exertions. When gripping, anterior and middle deltoid activity decreased by 2% MVE, while posterior deltoid, infraspinatus and trapezius activity increased by 2% MVE and biceps brachii activity increased by 6% MVE. Increased biceps brachii activity with gripping may be an initiating factor for the changes in shoulder muscle activity. The finding that hand gripping altered muscle activation, and thus the internal loading, of the shoulder may play an important role in shoulder injury development and rehabilitation. |
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