Head and shoulder posture affect scapular mechanics and muscle activity in overhead tasks

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Abstract

Forward head and rounded shoulder posture (FHRSP) is theorized to contribute to alterations in scapular kinematics and muscle activity leading to the development of shoulder pain. However, reported differences in scapular kinematics and muscle activity in those with forward head and rounded shoulder posture are confounded by the presence of shoulder pain. Therefore, the purpose of this study was to compare scapular kinematics and muscle activity in individuals free from shoulder pain, with and without FHRSP. Eighty volunteers were classified as having FHRSP or ideal posture. Scapular kinematics were collected concurrently with muscle activity from the upper and lower trapezius as well as the serratus anterior muscles during a loaded flexion and overhead reaching task using an electromagnetic tracking system and surface electromyography. Separate mixed model analyses of variance were used to compare three-dimensional scapular kinematics and muscle activity during the ascending phases of both tasks. Individuals with FHRSP displayed significantly greater scapular internal rotation with less serratus anterior activity, during both tasks as well as greater scapular upward rotation, anterior tilting during the flexion task when compared with the ideal posture group. These results provide support for the clinical hypothesis that FHRSP impacts shoulder mechanics independent of shoulder pain.

Introduction

Shoulder pain is reported to occur in up to 21% of the general population (Urwin et al., 1998) and is thought to be the result of extrinsic risk factors such as repetitive overhead use (>60° of shoulder elevation), sustained overhead work, and higher loads raised above shoulder height (Niosh, 1997). While these may be important they are likely difficult to modify as many occupational and athletic activities require repetitive overhead activity. Intrinsic risk factors such as forward head and rounded shoulder posture (FHRSP) (Szeto et al., 2002) and altered scapular kinematics and muscle activity (Ludewig and Cook, 2000) are reported in patients with shoulder pain. FHRSP is believed to alter scapular kinematics and muscle activity placing increased stress on the shoulder, leading to shoulder pain and dysfunction (Kendall et al., 1952, Roddey, 2002, Sahrmann, 2001). It is important to understand the effects of FHRSP on scapular kinematics and muscle activity because FHRSP has been shown to be modifiable (Wang et al., 1999, Falla et al., 2007) and may provide a pathway to improve shoulder mechanics and decrease the risk to develop shoulder pain.

Poor posture as defined by increased forward head (Ludewig and Cook, 1996), greater thoracic kyphosis (Finley et al., 2003, Kebaetse, 1999) and a more anterior shoulder position (Borstad and Ludewig, 2005, Wang et al., 1999) have been demonstrated to be associated with altered scapular position, kinematics, and muscle activity. Alterations in scapular kinematics and muscle activity have also been reported in patients with shoulder impingement syndrome and rotator cuff disease (Ludewig and Cook, 2000, Mcclure et al., 2004). However, research has not shown a clear relationship between the presences of FHRSP in individuals with shoulder pain (Greenfield et al., 1995, Lewis et al., 2005, Greigel-Morris, 1992). A major limitation in these studies is the presence of shoulder pain during testing, which makes it difficult to determine if differences in posture, scapular kinematics, or muscle activity are the cause of underlying shoulder pathology or are the result of shoulder pain. Additionally, these studies have tended to use non-functional planar tasks which do not reflect shoulder function in overhead tasks (Amasay and Karduna, 2009). Therefore, examination of scapula kinematics and muscle activity in individuals with FHRSP and without shoulder pain during a functional task is warranted.

The purpose of this study was to compare scapular kinematics and muscle activity in individuals free from shoulder pain, with and without FHRSP. We hypothesized that individuals with FHRSP would display less scapular upward rotation as well as greater internal rotation and anterior tilting. We also hypothesized that individuals with FHRSP would display less serratus anterior activity, and lower trapezius activity as well as greater upper trapezius activity compared to individuals with ideal head and shoulder posture.

Section snippets

Postural analysis

While FHRSP has been described clinically for over 50 years, we were unable to identify objective criteria that have been consistently used to define FHRSP. Therefore, we screened 310 volunteers from the university population to determine ideal (head over shoulders and acromion in line with trunk) and FHRSP. Prior to testing participants completed an informed consent form and underwent a postural screening to identify FHRSP. Posture was assessed using the BioPrint® postural analysis system

Subject demographics

There were no differences between age (F(1,79) = 0.83; p = 0.77) and thoracic kyphosis angle (F(1,79) = 1.44; p = 0.24) between groups (Table 1). There was a significant difference between forward head (F(1,79) = 285; p < 0.01) and shoulder angle between groups (F(1,79) = 284; p < 0.01) as well as mass (F(1,79) = 23.5; p < 0.01) with the FHRSP group being heavier (Table 1). Given the difference in mass all analyses were performed with and without mass as a covariate. However, no statistical differences were

Discussion

Individuals with FHRSP displayed greater scapular internal rotation as well as anterior tilting throughout the flexion task concurrent with less serratus anterior activity during the ascending phase of the shoulder flexion task. Similarly, greater scapular internal rotation concurrent with less serratus anterior activity were observed during the overhead reaching task. Individuals with FHRSP also displayed greater scapula upward rotation during the upper ranges of shoulder elevation during the

Conflict of Interest

The authors declare that there are no conflicts of interest.

Acknowledgments

This study was funding in part by the University of North Carolina-Chapel Hill Graduate School’s and Injury Prevention and Research Center’s student grant programs.

Charles Thigpen is a Clinical Research Scientist with Proaxis Therapy and Consulting Assistant Professor with the Doctor of Physical Therapy Division at Duke University. He completed his Ph.D. in Human Movement Science from the University of North Carolina-Chapel Hill in 2006. He has presented at the national and international conferences, and teaches in both the academic and continuing education arenas. He is currently leading several funded studies including: “A Randomized Control Trial for

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    Charles Thigpen is a Clinical Research Scientist with Proaxis Therapy and Consulting Assistant Professor with the Doctor of Physical Therapy Division at Duke University. He completed his Ph.D. in Human Movement Science from the University of North Carolina-Chapel Hill in 2006. He has presented at the national and international conferences, and teaches in both the academic and continuing education arenas. He is currently leading several funded studies including: “A Randomized Control Trial for Treatment of Shoulder Impingement”, “Prospective Evaluation of Risk Factors in Adolescent Baseball Players”, and “Adaptations to Pitching Over Time in Professional Baseball Pitchers”.

    He served as the staff athletic trainer for the 2002-2003 University of North Carolina women’s basketball team. Before that, Chuck worked as a graduate assistant with UNC wrestling, men’s lacrosse, women’s golf, and women’s crew. His primary research interest is shoulder injury, rehabilitation and prevention.

    He completed a M.S. in Human Movement Science with a concentration in Sports Physical Therapy from UNC in May of 2003. He earned his B.S. in Physical Therapy from East Tennessee State University in 1997.

    He is a NATABOC certified athletic trainer and a member of the National Athletic Trainer’s Association, as well as the American Physical Therapy Association’s Sports Physical Therapy and Orthopedic Special Interest Groups. He is currently serving as the Education Chair for the American Society of Shoulder and Elbow Therapists.

    Darin A. Padua, PhD, ATC is an Associate Professor in the Department of Exercise and Sport Science and Director of the Sports Medicine Research Laboratory. He is an adjunct faculty member in the following Departments at UNC: Orthopaedics, Biomedical Engineering, and Allied Health Sciences. Dr. Padua serves as the Director of the National Academy of Sports Medicine (NASM) Research Institute and is the acting Chair of the Research Committee for the National Athletic Trainers’ Association Foundation. Dr. Padua received his B.A. and M.A. degrees in Athletic Training from San Diego State University (1996) and the University of North Carolina at Chapel Hill (1998), respectively. He earned his PhD in Sports Medicine from the University of Virginia in 2001. His primary research interests focus on neuromuscular control of knee and lumbo-pelvic stability, identification of risk factors associated with knee injury, identification of evidence based prevention strategies for ACL injury, and validation of performance enhancement training techniques. Current research includes investigating predictive factors for ACL injury, biomechanical comparison of ACL injury prevention interventions, examination of modifiable neuromuscular factors that contribute to knee valgus angle and anterior tibial shear force, validation of clinical movement assessment techniques to predict muscle imbalances and injury risk, and validation of corrective exercises commonly used for injury prevention and performance enhancement.

    Lori A. Michener, PhD, PT, ATC, SCS is an Associate Professor in the Department of Physical Therapy at Virginia Commonwealth University – Medical College of Virginia Campus. She earned a B.S. in General Studies with a concentration in Athletic Training from Lock Haven University in PA as well as a B.S. in Physical Therapy from the State University of New York at Buffalo, a MEd from the University of Virginia, and earned her PhD in Orthopedics and Biomechanics from MCP Hahnemann University in Philadelphia, PA in 2001. Lori is the director of the COOR Laboratory (Clinical biomechanics, Orthopedics and sports medicine Outcomes Research) at VCU. Her research is focused on the study of diagnosis and treatment of orthopedic and sports injuries. Specifically, examining the ability to diagnosis rotator cuff disorders and labral pathology, treatment outcomes of conservative treatment for patients with rotator cuff disorders, and examining mechanisms underlying the shoulder pathologies using a variety of techniques to include ultrasonography, kinematics, and EMG. She currently is supported with 4 grants for her research.

    Kevin Guskiewicz, PhD, ATC is Professor and Chair in the University of North Carolina Department of Exercise and Sport Science. Kevin heads up the sport concussion program at UNC, while also serving as the Research Director for the Center for the Study of Retired Athletes. Kevin’s teaching responsibilities include Cadaver Anatomy, Therapeutic Modalities, Human Anatomy, and Research Methods & Statistics in Sports Medicine. Kevin’s research is focused on the assessment of sport-related concussion and the long-term effects of concussion. He has been the recipient of over 15 funded research grants on this topic, and has published over 45 journal articles and five textbook chapters related to concussion in sport. He serves as an Associate Editor for the Journal of Athletic Training, and is on the editorial boards of two other journals. Kevin was the recipient of the 1997 Kenneth Knight Outstanding Research Manuscript for the Journal of Athletic Training, the recipient of the 1999 NATA-REF New Investigator Award for Athletic Training Research, and the 2006 Medal for Distinguished Athletic Training Research. He was awarded Fellowship in the American College of Sports Medicine in May 2003, and was inducted as a Fellow in the American Academy of Kinesiology and Physical Education in September 2006. He and his wife Amy have 4 children Jacob, Nathan, Adam, and Tessa.

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    Jay D. Keener, MD is an Assistant Professor in Washington University Department of Orthopaedic Surgery. Jay earned his bachelor of science in physical therapy and his medical degree from the West Virginia University School of Medicine, Dr. Keener completed an orthopaedic surgery residency at the University of Iowa Hospitals and Clinics and fellowship training in shoulder and elbow reconstruction in the Department of Orthopaedic Surgery at Washington University School of Medicine. Before returning to Washington University as a faculty member in orthopaedic surgery, Dr. Keener was an assistant professor in the Department of Orthopaedic Surgery at the University of North Carolina School of Medicine, where he was honored with an Outstanding Instructor award for his musculoskeletal course. Jay is involved in a number of clinical outcome studies of reconstructive shoulder and elbow surgery, including: rotator cuff disease (partial and full thickness rotator cuff tears), shoulder and elbow arthritis, proximal humerus fractures, shoulder tendon transfers and labral/biceps tendon repairs.

    Nicholas Stergiou, PhD is an Isaacson Professor at the University of Nebraska at Omaha. He is also the Director of the Nebraska Biomechanics Core Facility and also holds an appointment of Professor in the Department of Environmental, Agricultural and Occupational Health Sciences at the University of Nebraska Medical Center. His research interests include nonlinear dynamics, variability and coordination of human movements, lower extremity function, infant postural development, and musculoskeletal injuries. Dr Stergiou’s research has been funded by the National Institutes of Health, the US Department of Education, the Nebraska Research Initiative and numerous foundations. He is also the Chair of the Education Committee of the American Society of Biomechanics. He has more than 90 Pubmed data-based publications and he is the Editor of a very popular textbook, the Innovative Analyses of Human Movement, from Human Kinetics Publishers.

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