Accepted Manuscript Predictor variables for forward scapular posture including posterior shoulder tightness Ji-Hyun Lee, MS Heon-seock Cynn, PhD Chung-Hwi Y, PhD Oh-yun Kwon, PhD TaeLim Yoon, MA PII:
S1360-8592(14)00062-X
DOI:
10.1016/j.jbmt.2014.04.010
Reference:
YJBMT 1118
To appear in:
Journal of Bodywork & Movement Therapies
Received Date: 22 August 2013 Revised Date:
26 March 2014
Accepted Date: 9 April 2014
Please cite this article as: Lee, J.-H., Cynn, H.-s., Y, C.-H., Kwon, O.-y., Yoon, T.-L., Predictor variables for forward scapular posture including posterior shoulder tightness, Journal of Bodywork & Movement Therapies (2014), doi: 10.1016/j.jbmt.2014.04.010. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Title page
Predictor variables for forward scapular posture including posterior
Authors name: 1) Ji-Hyun Lee1, MS, PhD student, PT (
[email protected]) 2) Heon-seock, Cynn1, PhD, PT, Professor (
[email protected]) 3) Chung-Hwi Y 2, PhD, PT, Professor (
[email protected])
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4) Oh-yun Kwon2, PhD, PT, Professor (
[email protected])
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shoulder tightness
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5) Tae-Lim Yoon1, MA, PhD candidate PT (
[email protected])
Affiliation: 1
Applied Kinesiology and Ergonomic Technology Laboratory, Department of Physical Therapy, Graduate School, Yonsei University, Won-ju, Republic of South Korea.
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Department of Physical Therapy, Graduate School, Yonsei University, Won-ju, Republic of South
Corresponding author: Heon-seock Cynn PT. PhD.
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Korea.
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Address: Applied Kinesiology and Ergonomic Technology Laboratory, Dept of Physical Therapy, Graduate School, Yonsei University, Wonju, Gangwon-do 220-710, Republic of South Korea.
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TEL: 82-33-760-2427, FAX: 82-33-760-2496 E-mail:
[email protected] We deny any conflicts of interest including personal, financial, or other related to our submitted manuscript titled “Predictor variables for forward scapular posture including posterior shoulder tightness.”
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Predictor variables for forward scapular posture including posterior
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shoulder tightness
3 Summary
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The purpose of this study was (1) to determine the relationships between the degree of forward
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scapular posture and the pectoralis minor index, the strength of the serratus anterior, the thoracic
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spine angle, and posterior shoulder tightness, and (2) to identify predictors of forward scapular
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posture, including posterior shoulder tightness. The study recruited eighteen subjects with forward
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scapular posture and objectively measured the acromion distance, the pectoralis minor index, and
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the strength of the serratus anterior muscle of each participant. The amount of glenohumeral
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horizontal adduction and internal rotation were evaluated to measure posterior shoulder tightness.
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There were high intra-rater reliabilities in all measurements. The measurement results showed a
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statistically strong negative correlation between the degree of forward scapular posture and the
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pectoralis minor index. They also revealed a moderate positive correlation between the degree of
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forward scapular posture and the thoracic spine angle and a moderate negative relationship between
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the degree of forward scapular posture and the amount of the glenohumeral horizontal adduction. A
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multiple regression analysis indicated that a total multiple regression model explained 93% of the
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amount of forward scapular posture. All predictor variables, including posterior shoulder tightness,
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should be considered while assessing, managing, and preventing forward scapular posture.
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Keywords: Forward scapular posture, Posterior shoulder tightness, Predictor.
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Forward scapular posture is protraction and anterior tilting of the scapula (the lateral scapular
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movement around the thorax) (Wu et al 2005). The condition is attributed to various shoulder
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disorders, such as subacromial impingement, adhesive capsulitis, and brachial plexus radiculitis
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(Kuhn et al 1995). Moreover, an altered scapular position may decrease glenohumeral rotation
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range of motion and strength (Smith et al 2002; Smith et al 2006), and alter neuromuscular
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activation patterns (Cools et al 2004). Consequently, these shoulder complications reduce the
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functional ability of the shoulder (Lin et al 2006) and the quality of life of the patient (Chipchase et
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al 2000).
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Several factors may cause forward scapular posture such as, muscle imbalance, soft tissue
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damage, poor posture, and repeated overhand motion (Burkhart et al 2000; Decker et al 1999;
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Finley and Lee 2003; Ha et al 2012; Laudner et al 2006; Ludewig and Cook 1996; Moseley et al
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1992; Wang et al 1999). The most common indicator is decreased flexibility or shortness of the
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pectoralis minor, which may give rise to forward scapular posture (Borstad and Ludewig 2005).
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Injury of the long thoracic nerves that innervate the serratus anterior muscle (Martin and Fish 2008)
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or weakness of the serratus anterior muscle itself, without nerve involvement, can also cause
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forward scapular posture since the serratus anterior helps to stabilize the inferior angle of the
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scapula against the posterior thoracic wall (Ekstrom et al 2004). Greater thoracic kyphosis may alter
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the scapular position significantly (Kebaetse et al 1999; Finley and Lee 2003), tending to increase
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scapular protraction (Ayub 1991; Grimsby and Gray 1997) and anterior tilting (Ha et al 2012),
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which diminishes range of motion and function of the shoulder (Briggs et al 2007; Chipchase et al
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2000). Consequently, the length of the pectoralis minor, weakness of the serratus anterior, and
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greater thoracic kyphosis have all been targeted in the treatment of forward scapular posture.
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Additionally, posterior shoulder tightness has been associated with changes in glenohumeral
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range of motion (Laudner et al 2006; Tyler et al 2000) and is common in subjects with forward
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scapular posture. Prior studies have neglected to investigate posterior shoulder tightness as a
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possible cause of forward scapular posture or have neglected to determine the association between
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the degree of forward scapular posture and posterior shoulder tightness. Therefore, this study
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proposed to (1) determine the relationships between the degree of forward scapular posture and the
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pectoralis minor index, the strength of the serratus anterior, the thoracic spine angle, and posterior
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shoulder tightness (the amount of glenohumeral horizontal adduction and internal rotation), and (2)
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identify predictors of forward scapular posture, including posterior shoulder tightness. The
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researchers hypothesized that (1) there would be moderate to strong correlations between the degree
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of forward scapular posture and the pectoralis minor index, the strength of the serratus anterior, the
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thoracic kyphosis angle, and posterior shoulder tightness (glenohumeral horizontal adduction and
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internal rotation), and (2) the pectoralis minor index (shortness), the strength of the serratus anterior,
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the thoracic spine angle, and posterior shoulder tightness would all predict the degree of forward
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scapular posture.
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METHODS
63 Subjects
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We recruited 28 subjects in the beginning of the study. Eighteen subjects (male 8, female 10) with
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forward scapular posture participated in this study through measuring forward scapular posture.
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Forward scapular posture was confirmed by measuring the distance between the anterior border of
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the acromion and the wall in standing posture (Peterson et al 1997; Struyf et al 2009); a distance
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equal to or greater than 7 cm indicated forward scapular posture. The study measured test-retest
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reliability of acromion distance for measuring forward scapular posture; the intra-class correlation
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coefficient (ICC) was 0.90 (95% confidence interval: 7.60-8.99). The mean and standard deviation
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of age, weight, and height were 33.78±11.15 years, 57.81±9.10 kg, and 1.64±0.07 m, respectively.
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The dominant arm (the preferred arm when performing eating and writing tasks) was used in all
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tests (Yoshizaki et al., 2009). All subjects were at least 18 years of age and right side dominant.
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Advertising and personal contact recruited the volunteers. Clinical screening tests (shoulder active
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range of motion, impingement, and glenohumeral instability/apprehension tests) of all subjects
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ensured that no underlying pathologies existed in the dominant shoulders. (Borstad and Ludewig
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2005). The study excluded those who reported existing shoulder pathologies, histories of shoulder
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surgeries, orthopedic or neurological disorders, current shoulder pain limiting activities, or regular
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physical training involving the dominant shoulder.
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Procedures
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The intra-rater reliability of all measurements was examined by a licensed physical therapist with
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10 years of clinical experience. The assessor measured each of the following twice: the acromion
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distance, for forward scapular posture definition, the pectoralis minor muscle length, the thoracic
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spine angle, serratus anterior muscle strength, and the amount of glenohumeral horizontal adduction
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and internal rotation, and
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University Institutional Review Board approved the study protocol and each subject gave informed
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consent prior to data collection.
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Pectoralis minor muscle length test (pectoralis minor index)
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The subjects gazed straight ahead to ensure a consistent standing posture. To measure the length of
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the pectoralis minor, marks were made on the skin over the inferomedial aspect of the coracoid
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process and the caudal edge of the fourth rib adjacent to the sternum, which are the origin and the
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insertion of the pectoralis minor, respectively. The assessor measured the distance between the two
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with a soft tape measure. The values were normalized by dividing the resting length of the
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used the mean values from the two measurements. The Yonsei
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pectoralis minor muscle by the subject’s height and multiplying by 100 (ICC = 0.96) (Borstad and
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Ludewig 2005).
99 Serratus anterior muscle strength test
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Each subject was seated on a bench with upper extremities resting beside the body. A dynamometer
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(Lafayette instrument company, North Lafayette, USA) was placed on the humerus distal to the
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deltoid attachment. The assessor stabilized the inferior angle of the target scapula, while matching
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the force of the subject. He/she then instructed each subject to protract the scapula fully with
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shoulder flexion of 130° and full elbow extension against a hand-held dynamometer for a 5-second
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maximal isometric contraction. Subjects were instructed to avoid holding the bench with their
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uninvolved upper extremities, holding their breath, or making other compensatory movements
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during testing. Numerous studies have previously established that shoulder flexion or abduction
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exercise between 120° and 150° produces maximum electromyography activity of the serratus
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anterior muscle (ICC = 0.90) (Ekstrom et al 2004; McClure et al 2004; Moseley et al 1992).
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Thoracic spine angle measurement in sagittal plane
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To ensure a consistent standing posture, the subjects gazed straight ahead while four reflective
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markers were placed over the T1, T3, T12, and L1 vertebrae and were photographed using a digital
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camera, placed 2 m from the lateral side of the trunk. Image J software, downloaded from the
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internet without cost, and calculated the thoracic spine angles from the digital images (Abràmoff et
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al 2004; Rasband 2008; Kuo et al 2009). We downloaded Image J software on the internet freely;
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we pressed on the angle tool icon, and then clicked the T1, T3, T12, and L1 vertebrae in sequence.
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Thoracic spine angle was calculated in the status bar automatically. The angle values were exported
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to a Microsoft Excel spreadsheet. A positive thoracic angle indicated flexion and a negative lumbar
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angle indicated extension. The intra-rater reliability of skin marker placement was good (ICC = 0.
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91) (Kuo et al 2008; Tully et al 2005) (Figure 1A, B).
123 Posterior shoulder tightness test (the amount of glenohumeral horizontal adduction)
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Assessors instructed each subject to lie supine with upper extremities resting beside his/her body on
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the table. The assessor stood beside the table and positioned the test shoulder with the elbow in 90°
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flexion and the shoulder abducted 90°. The assessor stabilized the lateral border of the scapula by
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providing a dorsally directed force to control scapular protraction, rotation, and abduction. The
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assessor held the forearm, and then moved the humerus into horizontal adduction passively until the
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limit of movement. An assessor recorded the range of motion for horizontal adduction using a
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digital inclinometer (GemRed DBB, Gain Express Holdings, Ltd., Hong Kong, China) aligned with
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the ventral midline of the humerus. Previous studies have confirmed that this measurement is an
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appropriate standard for assessing posterior shoulder tightness (ICC = 0.90) (Laudner et al 2006;
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Pappas et al 1985; Warner et al 1990;).
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Posterior shoulder tightness test (the amount of glenohumeral internal rotation)
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To measure the amount of glenohumeral internal rotation, the subject was positioned supine with
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the shoulder abducted 90° and the elbow flexed 90° to ensure a neutral horizontal position. The
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humerus was passively rotated internally with the assessor stabilizing the scapula with his other
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hand. In this position, the digital inclinometer was placed on dorsal surface of the forearm aligned
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with the long axis of the ulna for reference. A second assessor measured the angle between the
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forearm and a plane perpendicular to the table. This study used the glenohumeral internal rotation
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measurement to investigate posterior shoulder tightness because the posterior glenohumeral muscles
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consist of the joint capsule and rotator cuff muscles, including the posterior deltoid, infraspinatus,
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teres minor, and subscapularis (Warner et al 1990). Some of these muscles, such as the infraspinatus
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and the teres minor, produce and control shoulder external rotation. Short posterior glenohumeral
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muscles that are glenohumeral external rotators might also limit glenohumeral internal rotation
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(ICC = 0.95) (Burkhart et al 2003; Ellenbecker et al 1996; Pappas et al 1985).
149 Statistical analysis
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Kolmogorov–Smirnov Z-tests assessed distribution normality. All variables were in normal
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distribution. The ICC (3, 2) model was selected to test intra-rater reliability. ICCs determined intra-
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rater reliabilities for measurements of forward scapular posture, posterior shoulder tightness, the
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length of the pectoralis minor, the strength of the serratus anterior, and the thoracic kyphosis angle.
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Pearson’s correlation coefficient (r) determined the magnitude of the correlations between the
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degree of forward scapular posture and (1) the pectoralis minor index, (2) the strength of the
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serratus anterior, (3) the thoracic kyphosis angle, and (4) posterior shoulder tightness, with the
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coefficient of determination being a percentage of R2.
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Collinearity statistics performed to evaluate collinearity of variables before multi linear
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regression model. There was no multicollinearity among all explanatory variables. Forward variable
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selection is used to identify the explanatory variables that are significantly related to the response
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variable in building a multiple regression model. All variables are statistically significant in the
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model. First, simple linear regression predicted the degree of forward scapular posture based on the
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pectoralis minor index (r2). Second, multiple regression explained the degree of forward scapular
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posture through the pectoralis minor index, the strength of the serratus anterior, and the thoracic
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spine angle (R2). Finally, this study added the amount of glenohumeral horizontal adduction and
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internal rotation to the multiple regressions (R2). To measure how well posterior shoulder tightness
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can predict forward scapular posture, the researchers performed multiple regression analyses with
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forward scapular posture as the dependent variable, and with the pectoralis minor index, the
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strength of the serratus anterior, the thoracic spine angle, glenohumeral horizontal adduction, and
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internal rotation as independent variables. All statistical analyses used PASW Statistics 18 and 0.05
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indicated statistical significance.
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RESULTS
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Table 1 shows the mean and standard deviation values for the amount of forward scapular posture,
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the length of the pectoralis minor, the pectoralis minor index, the strength of the serratus anterior,
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the thoracic spine angle, glenohumeral horizontal adduction, and glenohumeral internal rotation.
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There were high intra-rater reliabilities in all measurements: amount of forward scapular posture
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(ICC3, 2 = 0.90), pectoralis minor length (ICC3, 2 = 0.96), strength of the serratus anterior (ICC3, 2=
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0.90), thoracic kyphosis angle (ICC3, 2 = 0.91), glenohumeral horizontal adduction (ICC3, 2 = 0.90),
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and glenohumeral internal rotation (ICC3, 2 = 0.95).
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There was a statistically significant strong negative correlation between the degree of forward
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scapular posture and the pectoralis minor index (r=–0.89, p=.000), a moderate positive correlation
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between the degree of forward scapular posture and the thoracic spine angle (r=0.72, p=.001) and a
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moderate negative correlation between amount of the glenohumeral horizontal adduction (r=–0.72,
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p=.001). By contrast, there were fair negative correlations between the degree of forward scapular
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posture and the strength of the serratus anterior (r=–0.43, p=.077) and the amount of glenohumeral
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internal rotation (r =–0.39, p =.107) (Table 2).
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The adjusted coefficient of determination r2 was 0.78 (F=59.50, p=.000) for the simple regression
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of the forward scapular posture on the pectoralis minor index. This means that the pectoralis minor
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index accounted for only 78% of the variance in forward scapular posture. A multiple regression
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equation was developed to predict forward scapular posture from the pectoralis minor index, the
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strength of the serratus anterior, and the thoracic spine angle. The resulting equation was forward
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scapular posture = 12.37 – 0.70 (the pectoralis minor index) - 0.27 (serratus anterior strength) + 10
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0.23 (thoracic spine angle). The adjusted coefficient of determination R2 for this equation was 0.88.
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To determine predictability after adding posterior shoulder tightness, forward scapular posture
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became the dependent variable and the pectoralis minor index, and the strength of the serratus
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anterior, the thoracic spine angle, the amount of glenohumeral horizontal adduction, and the amount
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of glenohumeral internal rotation became independent variables. The adjusted coefficient of
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determination R2 was 0.93; thus, with this model, the total explained variance in the forward
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scapular posture was 93% (F=29.42, p=.000). The equation developed from the four predictors was
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forward scapular posture = 11.15 – 0.49 (pectoralis minor index) - 0.36 (serratus anterior strength) +
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0.27 (thoracic spine angle) – 0.03 (glenohumeral horizontal adduction) – 0.13 (glenohumeral
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internal rotation).
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DISCUSSION
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Forward scapular posture influences altered scapular kinematics and scapulothoracic muscle
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imbalance, which are issues reported in rotator cuff disease and shoulder impingement syndrome
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(Ludewig and Cook 2000; McClure et al 2004). There are various muscular skeletal factors of
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forward scapular posture including repetitive overhand movement (in overhand athlete) and
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habitual slouched postural in everyday tasks (Burkhart et al., 2003; Chansirinukor et al., 2001;
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Magee, 1992). Especially, the length of the pectoralis minor, the strength of the serratus anterior,
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and the thoracic spine angle are important in the management of forward scapular posture (scapular
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protraction and anterior tilting). However, no previous studies have investigated the relationships
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between the degree of forward scapular posture and other possible factors, including posterior
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shoulder tightness. Thus, the present study was conducted to investigate the correlation and
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coefficient of determination for forward scapular posture.
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The pectoralis minor is lengthened during glenohumeral external rotation, scapular upward 11
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rotation, scapular posterior tilting (Ludewig and Cook 2000; McClure et al 2001). Increased tension
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of the pectoralis minor may affect scapular kinematics and reduce subacromial space, creating an
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environment conducive to pathologies such as impingement syndrome (Hebert et al 2002; Ludewig
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and Cook 2000). This study found a strong negative relationship between the degree of forward
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scapular posture and the pectoralis minor index (r = –0.89, P= .000). Our first hypothesis was
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entirely supported. This is analogous to pectoralis minor shortness causing scapular anterior tilting
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in the sagittal plane (Borstad and Ludewig 2005), where it also increases scapula internal rotation
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and anterior tilting. Previous study indicated scapula dyskinesis and malposition associated with the
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length of the pectoralis minor (Burkhart et al 2000), which may have produced scapular tilting
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motion (Escamilla et al 2009). The results of the current study support this theory. Accordingly,
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pectoralis minor lengthening exercises have been advocated to manage forward scapular posture
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clinically.
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The serratus anterior is one of the prime muscles to keep all components of healthy scapular
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movements (Ludewig and Cook 1996; McClure et al 2001). Specifically, the serratus anterior
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stabilizes the medial border and inferior angle of the scapula, which revokes scapular anterior tilting
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(Ebaugh et al 2005; McClure et al 2001). Previous investigators have explained how the serratus
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anterior controls the movement of the scapula and that reduced serratus anterior activity contributes
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to altered scapula kinematics, such as scapular winging (Ludewig and Cook 2000). Weakness of the
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serratus anterior is often related with improper scapular anterior tilting and protraction (Kuhn et al
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1995; Warner and Navarro 1998). The current study measured the strength of the serratus anterior to
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determine the relationship between forward scapular posture and the strength of the serratus anterior.
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Interestingly, the results showed a fair negative correlation between the degree of forward scapular
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posture and the strength of the serratus anterior. Our hypothesis was partially supported. Forward
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scapular posture is not related only to the strength of the serratus anterior, but may also be
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associated with the strength of the lower trapezius (Ludewig et al 2004) or the length of the
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pectoralis minor, which is a major cause of forward scapular posture. However, no studies have
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explored scapular muscle performance dependent on the relative balance of scapular muscles. Thus,
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further study is required to investigate ratios of muscle performance between the pectoralis minor
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and the serratus anterior or other scapular muscles.
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Slouched posture and repeated overhand throwing motion also lead to scapular anterior tilting
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and upward rotation in the scapular plane (Kebaetse et al 1999). The altered scapular kinematic and
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muscle activity places increased stress on the shoulder, leading to shoulder pain and dysfunction
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(Roddey et al 2002; Sahrmann, 2002). Previous studies have indicated that excessive thoracic
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kyphosis increased scapular protraction (Ayub 1991; Grimsby and Gray 1997). Kebate et al.(1999)
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also reported that the scapula was significantly elevated and that less scapular posterior tilting
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occurred during arm abduction in the slouched posture (more thoracic flexion). Results of the
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current study showed a moderate positive correlation (r = 0.72, P= .001). However, there was no
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significant difference in thoracic kyphosis between the forward head and round shoulder posture
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group and the healthy group (Thigpen et al 2010). Thus, the authors acknowledge that this issue is
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open to dispute.
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Posterior shoulder tightness is a common observation in the clinical setting. Excessive posterior
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shoulder muscle shortness may be related to altered acromioclavicular and sternoclavicular joint
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movement (Wong et al 2010). This study measured the amounts of both glenohumeral horizontal
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adduction and internal rotation to determine posterior shoulder tightness. The results showed a
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strong negative correlation between the degree of forward scapular posture and the amount of
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glenohumeral horizontal adduction and a fair negative correlation between the degree of forward
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scapular posture and the amount of glenohumeral internal rotation. As a result, our hypothesis was
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partially supported. To the author’s knowledge, this is the first study to demonstrate a connection
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between the length of the posterior glenohumeral muscles and forward scapular posture; therefore,
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comparison of the results is impossible. Pappas et al (1985) reported that posterior shoulder
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tightness was increased with forward scapular posture because the movement occurs toward the
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path of least resistance (Pappas et al 1985; Sahrmann 2002). One explanation may be that posterior
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shoulder tightness increases forward scapular posture as the tight posterior shoulder structures,
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relative to the scapulothoracic muscles, pull the scapula forward (Myers et al 2006). Considering
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these results, posterior shoulder tightness (reduced flexibility or increased stiffness) likely leads to
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more flexible, less stiff scapulothoracic joint movement (forward scapular posture in the horizontal
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plane) by pulling the scapula forward in horizontal adduction. This indicates that for each degree
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that forward scapular posture increases, the range of glenohumeral horizontal adduction (i.e.,
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posterior shoulder tightness) decreases. Pectoralis muscle shortness can increase the amount of
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glenohumeral internal rotation without posterior shoulder tightness, and humeral torsion may affect
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the range of glenohumeral internal rotation (Crockett et al 2002; Reagan et al 2002). Humeral
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retroversion has resulted from increased glenohumeral external rotation and decreased internal
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rotation, not including posterior shoulder tightness. To author’s knowledge, this is the first study to
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demonstrate that the length of the posterior glenohumeral muscles can explain forward scapular
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posture and that shortening of the posterior glenohumeral muscles may influence forward scapular
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posture in healthy individuals. However, it is still equivocal whether posterior shoulder tightness
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causes forward scapular posture since it is possible that forward scapular posture results in posterior
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shoulder tightness. Further study is required to elucidate the cause-and-effect relationship.
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Multiple regression analyses explored how well forward scapular posture could be explained by
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the pectoralis minor index, the strength of the serratus anterior, the thoracic kyphosis angle, and
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glenohumeral horizontal adduction (posterior shoulder tightness). In a simple regression of forward 14
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scapular posture on the pectoralis minor index, R2 = 0.78, i.e., the length of the pectoralis minor
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accounted for 78% of the variance in forward scapular posture. A short pectoralis minor produces a
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more internally rotated scapula and posterior tipping (Borstad and Ludewig 2005); however, the
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pectoralis minor index is insufficient to predict forward scapular posture entirely. Adding the
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strength of the serratus anterior and the thoracic spine angle to the multiple regression analyses
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explained 88% of the variance (R2 = 0.88). Excessive thoracic kyphosis can alter scapular
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kinematics in resting posture (Kibler and McMullen 2003). Finally, when glenohumeral horizontal
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adduction was added to the equation, the prediction of forward scapular posture improved to R2 =
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0.93 for this equation. Therefore, posterior shoulder tightness contributed 5% more to the prediction
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of forward scapular posture. All four variables can be significant contributors to explain forward
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scapular posture. Clinically, posterior shoulder tightness should be assessed using the horizontal
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adduction range of motion. The standard physical therapy protocol does not include determining the
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length of the posterior glenohumeral muscles. In addition, exercises for the posterior glenohumeral
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joint might be options in forward scapular posture interventions.
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Study limitations
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There are several limitations to this study. First, the simple measuring of the glenohumeral internal
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rotation range to determine posterior glenohumeral muscle shortness may be misleading due to the
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strong relationship between increased humeral retroversion and glenohumeral internal rotation
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range. Second, as this was a cross-sectional study, causal relationships cannot be demonstrated; for
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example, posterior shoulder tightness might cause forward scapular posture or vice versa. Third,
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this study did not consider any interaction terms or adding demographic factors. Fourth,
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generalization of the study is limited because a small number of subjects participated and the high
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number of variables to the number of subjects. Future longitudinal studies with a larger sample size
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are required to determine a cause and effect relationship between forward scapular posture and
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posterior shoulder tightness.
323 CONCLUSIONS
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The study examined the relationship between forward scapular posture and related predictor
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variables. The findings demonstrated moderate to high correlations between forward scapular
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posture and the pectoralis minor index, the strength of the serratus anterior, the thoracic spine angle,
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and posterior shoulder tightness. The pectoralis minor index predicted only 78% of the forward
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scapular posture in a simple regression. Posterior shoulder tightness improved the prediction of
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forward scapular posture by 5%. Multiple regression analyses, including glenohumeral horizontal
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adduction, the strength of the serratus anterior, the pectoralis minor index, and the thoracic spine
332
angle as independent variables, explained 93% of the variance in forward scapular posture.
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Therefore, Assessments of the length of the pectoralis minor, the strength of the serratus anterior,
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the thoracic spine angle, and posterior shoulder tightness would be recommended for forward
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scapular posture in physical therapy and clinical management.
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Table 1 The raw data of forward scapular posture, pectoralis minor index, strength of the serratus anterior, thoracic kyphosis angle, and glenohumeral range of motion Parameters
Values
Glenohumeral horizontal adduction (°)
±
1.50
7.6 to 8.99
28.75 ±
11.98
23.21 to 34.29
Glenohumeral internal rotation (°)
54.08 ±
13.13
48.01 to 60.15
Length of the pectoralis minor (cm)
12.5
±
4.22
Pectoralis minor index
7.65
±
2.64
Strength of the serratus anterior (pound)
48.13 ±
11.98
Thoracic kyphosis angle (°)
33.77 ±
8.37
Values are presented as mean ± SD
2 3
10.55 to 14.45
6.43 to 8.87
42.59 to 53.67
29.90 to 37.64
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Amount of forward scapular posture (cm)
CI (95%)
Table 2 Pearson correlation coefficients (r) between forward scapular posture and pectoralis minor index, strength of the serratus anterior, thoracic kyphosis angle, and
Parameters
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glenohumeral range of motion
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Glenohumeral horizontal adduction Glenohumeral internal rotation Pectoralis minor index Strength of the serratus anterior Thoracic kyphosis angle a p < 0.05 (n=18)
7 8 9 10 21
Forward scapular posture r -0.72 -0.39 -0.89 -0.43 0.72
p 0.001a 0.107 0.000 0.077 0.001
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A caption list of the figure
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Figure 1 Thoracic spine angle measurement in sagittal plane
3
(A) Placement of markers
4
(B) Thoracic angle definition
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ACCEPTED MANUSCRIPT Table 1. The raw data of forward scapular posture, pectoralis minor index, strength of the serratus anterior, thoracic kyphosis angle, and glenohumeral range of motion CI (95%) 7.6 to 8.99
Glenohumeral horizontal adduction (°)
28.75 ± 11.98
23.21 to 34.29
Glenohumeral internal rotation (°)
54.08 ± 13.13
48.01 to 60.15
Length of the pectoralis minor (cm) Pectoralis minor index Strength of the serratus anterior (pound) Thoracic kyphosis angle (°) Values are presented as mean ± SD
12.50 7.65 48.13 33.77
± ± ± ±
10.55 to 14.45 6.43 to 8.87 42.59 to 53.67 29.90 to 37.64
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Values 8.30 ± 1.50
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4.22 2.64 11.98 8.37
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Parameters Amount of forward scapular posture (cm)
ACCEPTED MANUSCRIPT Table 2 Pearson correlation coefficients (r) between forward scapular posture and pectoralis minor index, strength of the serratus anterior, thoracic kyphosis angle, and glenohumeral range of motion Forward scapular posture r -0.72 -0.39 -0.89 -0.43 0.72
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Glenohumeral horizontal adduction Glenohumeral internal rotation Pectoralis minor index Strength of the serratus anterior Thoracic kyphosis angle a p < 0.05 (n=18)
p 0.001a 0.107 0.000 0.077 0.001
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Editor-in-Chief, Journal of Bodywork & Movement Therapies