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Tuesday, June 6, 2023

Head and Shoulder Posture Affect Scapular Mechanics and Muscle Activity in Overhead Tasks

Brent Brookbush

Brent Brookbush


Research Review: Rounded Shoulder Posture without Excessive Thoracic Kyphosis and Shoulder Pain and its Influence on Scapular Kinematics and Muscle Activity

By Nicholas Rolnick SPT, MS, CSCS

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Thigpen CA, Padua DA, Michener LA, Guskiewicz K, Giuliani C, Keener JD, Stergiou N. (2010). Head and shoulder posture affect scapular mechanics and muscle activity in overhead tasks. Journal of Electromyography and Kinesiology. 20: 701-709. ABSTRACT

Why is this relevant?: Rounded shoulder posture (RSP) is a postural dysfunction frequently encountered in clinical and performance settings; associated with forward head, shoulder pain, excessive thoracic kyphosis (ETK), and altered scapular kinematics (1-2). However, since RSP commonly presents with ETK and shoulder pain, it is unclear whether scapular mechanics are affected in individuals without ETK and shoulder pain. This study investigated scapular kinematics and muscle activation patterns of the serratus anterior , and upper and lower trapezius in individuals with RSP, but without ETK or shoulder pain.

Study Summary

Study Design Cross-sectional Case Control
Level of Evidence Level 3: Case Controlled Study
Subject DemographicsAge and Gender: 18 - 60 years old in a University Setting
  • Postural assessment group (n = 310)
    • 34.2 +/- 11.9 years old

  • Study group (n = 80)
    • Ideal Posture 
      • Males (n = 21)
        • 32.6 +/- 13.3 years old

      • Females (n = 19)
        • 34.4 +/- 12.6 years old

    • Forward-Head Rounded-Shoulder Posture (FHRSP) group
      • Males (n = 15)
        • 39.1 +/- 12.5 years old

      • Females (n = 25)
        • 35.0 +/- 11.3 years old


  • Individuals who met the FHRSP group had Forward Head Angle (FHA - measured from C7 to the ear) greater than or equal to 46° and Forward Shoulder Angle (FSA - measured from C7 to the acromion) greater than or equal to 56° (see picture above for schematic)
    • 40 participants in data analysis

  • Individuals who met the ideal posture group had FHA less than or equal to 36° and FSA less than or equal to 22°
  • 40 participants in data analysis
    • Intraday Reliability 
      • Calculated with 20 total individuals (10 in FHRSP and 10 in ideal posture group) who were measured twice within the same day
        • Intra-class correlation coefficient (ICC) - 0.92 (Standard Error of the mean - SEM = 2°) for FHA
        • ICC for FSA - 0.89 (SEM = 5°)

      • Interday Reliability 
        • ICC - 0.78 (SEM = 4°) for FHA
        • ICC - 0.72 (SEM = 7°) for FSA

      • Initial Group Comparisons
        • No difference in:
          • age (p = 0.77)
          • thoracic kyphosis angle (p = 0.24)

        • Difference in:
          • FHRSP > FHA (p < 0.01) and FSA (p < 0.01) than ideal posture group
          • FHRSP heavier than ideal posture group (p < 0.01)
            • Analyses were done with/without mass as a covariate.  It was determined that mass did not influence results

      • Task Overview
        • Loaded arm flexion task
          • Weight equal to 3% of body weight (selected from pilot study results), following a 2-inch target on the wall while maintaining an extended elbow
            • target moved in the sagittal plane, in line with the acromion of the dominant arm

          • Participants lifted arm overhead throughout full available range of motion at a self-selected speed

        • Reaching task
          • weight equal to 3% of body weight (selected from pilot study results)
            • standardized starting and target position on a shelf
              • did not control for plane of elevation or elbow position

      • Muscles Recorded using surface EMG

      • Standardization of Maximum Voluntary Isometric Contraction (MVIC)
        • Separate MVICs and EMG setup for each muscle group in positions based on previous literature
        • 5 second isometric holds with 30 seconds in-between each trial
        • 1 minute between each muscle group tested
        • Repeated 3 times
        • Standardized instructions and encouragement
        • Each participant had practice trials for familiarization
        • Middle 1 second was calculated for each trial and averaged across the 3 trials
        • Values for the overhead flexion and reaching tasks were normalized for each of the various muscles and expressed as a percentage of MVIC (%MVIC)

      • Protocol Overview
        • Randomized task order for each participant, in each group with rest 5 minutes in-between tasks
        • 2nd-7th trial performance used reduce the effects of fatigue on outcomes (total of 25 repetitions for each task)

Inclusion Criteria:

  • Postural alignment criteria described above

Exclusion Criteria:

  • History of shoulder surgery
  • Current shoulder pain limiting activity
  • Upper extremity injuries limiting activity
  • Cervical or thoracic fracture
  • Displayed functional or structural scoliosis
  • Displayed excessive thoracic kyphosis ( > 50°)
Outcome MeasuresScapular rotation angles during ascending and descending phases of each exercise (flexion and reaching tasks)
  • Up/Down Rotation (at 60, 90, and 110-120° of humeral elevation)
  • Internal/External Rotation (at 60, 90, and 110-120° of humeral elevation)
  • Posterior/Anterior Tilt (at 60, 90, and 110-120° of humeral elevation)
    • Scapular muscle activity during ascending and descending phases of each exercise (flexion and reaching tasks)
      • Upper trapezius (at 60, 90, and 110-120° of humeral elevation)
      • Lower trapezius (at 60, 90, and 110-120° of humeral elevation)
      • Serratus anterior (at 60, 90, and 110-120° of humeral elevation)

**120 degrees was used for flexion task, 110 degrees for reaching task**

ResultsSignificant group affects for scapular internal rotation angle during both flexion ( p < 0.01) and reaching ( p < 0.01) tasks. FHRSP group exhibited greater scapular internal rotation angles than ideal posture group during both tasks. 
  • Mean difference of scapular internal rotation angles between groups was 8° (Effect size, ES = 0.52) for flexion task and 10° (ES = 0.60) for reaching task
  • Significant group by angle interaction during the flexion task (p < 0.01) with upward/downward rotation of the scapula.
    • FHRSP group displayed greater scapular upward rotation at 120° during ascending/descending phase of humeral elevation than ideal posture group (mean difference = 5°; ES = 0.51)

  • Significant effect of humeral elevation on anterior/posterior tilting angle during flexion task (p = 0.019).
    • FHRSP group displayed greater anterior tilting throughout ascending/descending phase of all humeral elevation angles when compared to ideal posture group.
      • mean difference = 3°; ES = 0.32 for ascending phase
      • mean difference = 4°; ES = 0.34 for descending phase

  • Significant interaction affect between humeral elevation phase by group on serratus anterior activity during flexion (p = 0.02) and reaching task (p = 0.04)
    • FHRSP group displayed less serratus anterior activation during both tasks when compared to ideal posture group
      • mean difference = 13% MVIC; ES = 0.38 for flexion task
      • mean difference = 6% MVIC; ES = 0.33 for reaching task


Individuals with FHRSP exhibited greater scapular internal rotation and anterior tilting with decreased serratus anterior activity during the ascending phase of the flexion task when compared to ideal posture group.

Individuals with FHRSP exhibited greater scapular internal rotation and less serratus anterior activity with the overhead reaching task when compared to ideal posture group.

Individuals with FHRSP exhibited greater scapular upward rotation during the upper ranges of shoulder elevation when compared to ideal posture group.

Conclusions of the ResearchersFHRSP influences shoulder kinematics independent of shoulder pain and excessive thoracic kyphosis in overhead tasks.

In RSP, excessive static and dynamic anterior tilting and internal rotation of the scapula results in impaired kinematics during overhead movements.
Caption: In RSP, excessive static and dynamic anterior tilting and internal rotation of the scapula results in impaired kinematics during overhead movements.

In RSP, excessive static and dynamic anterior tilting and internal rotation of the scapula results in impaired kinematics during overhead movements.

Review & Commentary:

Rounded shoulder posture (RSP) is a postural dysfunction frequently encountered in clinical and performance settings; associated with forward head, shoulder pain, excessive thoracic kyphosis (ETK), and altered scapular kinematics (1-2). Previous research on RSP (that did not distinguish scapular mechanics from ETK and shoulder pain) has shown that the scapula rests in a position of excessive internal rotation and anterior tipping, and exhibits less upward rotation in dynamic activities when compared to individuals without RSP (2-4). Previous research on ETK, has shown that this postural change is correlated with increased internal rotation and anterior tipping of the scapula (independent of pectoralis minor adaptive shortening), shoulder pain, and may decreases upward rotation during dynamic tasks (2,5).

The authors created a standard for defining RSP; as this had not previously been standardized. They screened 310 individuals from a university population for ideal posture, forward head angle, and forward shoulder angle

  • Ideal Posture - Head over shoulders and acromion in line with the trunk
  • Foward Head Angle (FHA) - Measured from C7 to the ear
  • Forward Shoulder Angle (FSA) - Measured from C7 to the acromion.

Individuals within the study were measured separately on three different days - each was asked to perform repeated neck motions and reaches overhead (in an effort to find neutral alignment), and then asked to stand in their resting posture before a picture was taken. The authors averaged the 3 data sets to determine mean FHA and FSA for each individual. Ideal posture was determined by creating groups based on FHA and FSA that were +/- 1 standard deviation away from the group mean. The authors used this new postural alignment criteria to compare healthy, pain-free individuals who had RSP without ETK, to those who exhibited their defined criteria of ideal posture in functional overhead activities.

The current study contributes to the body of evidence, by accounting for confounding variables (ETK and shoulder pain) that may have contributed to altered kinematics of the scapulothoracic complex (2, 4). The results of the study provide additional context for the role of RSP alone, on the kinematics of the scapulothoracic complex and its associated musculature. RSP in the absence of ETK and shoulder pain resulted in increased scapular internal rotation and anterior tilt and decreased axioscapular muscle activity (serratus anterior ), coinciding with previous research (3-4). The current study did show an increase in scapular upward rotation in individuals with RSP which is contrary to previous studies (3-4). The discrepancy can be explained by the authors controlling for ETK, as this has been shown to decrease scapular mobility (3). Interestingly, this investigation did not show changes in lower trapezius activity, despite a decrease noted in previous studies in populations exhibiting RSP (6).

Despite the strong methodology used in the study, the current study did have weaknesses that limit its application in a clinical setting. Although pain and ETK were purposefully excluded from the study, this may limit transfer of study outcomes to groups with shoulder pain or those with ETK. Further, since the study only measured to 120 degrees of humeral elevation, scapulothoracic movements above this elevation cannot be inferred, which may have accounted for why data on upward rotation of the scapula and lower trapezius activation did not coincide with previous research.

Why is this study important?

This study was the first to create an experimental methodology that quantifies ideal posture, and tested that methodology using a large sample of 310 individuals without shoulder pain and ETK. The study adds to the current body of literature, by adding to our understanding of Upper Body Dysfunction (UBD) and assessment, and confirms that rounded shoulder posture alone is enough to effect scapular kinematics.

How does it affect practice?

Research supports that shoulder pain, rounded shoulder posture (RSP), aberrant scapular kinematics, excessive thoracic kyphosis and forward head posture are related and may affect muscle strength and activity (1-2,4). Furthermore, interventions focusing on releasing and lengthening overactive synergists (pectoralis minor ) and activating and integrating under-active muscles (serratus anterior , lower trapezius , rotator cuff ) have been shown to be effective in restoring optimal alignment, scapular kinematics, and muscle strength (1,4,6). This study provides evidence that RSP alone may be enough to alter scapular motion and muscle activity during functional tasks. Further research is needed to determine if this may be predictive of further dysfunction and pain.

If optimizing motion is a rehab or training goal, the human movement professional should assess for postural faults and consider the potential impact on motion. Specifically, this study shows a correlation between rounded shoulders and excessive anterior tipping and internal rotation of the scapula, along with under-activity of the serratus anterior.

How does it relate to Brookbush Institute Content?

The Brookbush Institute’s predictive model of Upper Body Dysfunction (UBD)  includes the altered scapulothoracic mechanics described in this study as well as under-activity of the serratus anterior . This model reasons further that all muscles, joints, fascia and potentially nerves of the scapulothoracic and glenohumeral joints may be affected. The Brookbush Institute’s approach to UBD involves releasing  over-active muscles, mobilizing joints exhibiting arthrokinematic dysfunction, lengthening short structures, and activating and integrating long and under-active muscles to restore optimal motion. It is a tenant of the Brookbush Institute, that the “completeness” of an intervention (addressing all structures exhibiting maladaptive change) will contribute to the efficacy and carry-over of any intervention. This study is an important step toward evidence-based intervention for the correction of postural dysfunction and the resolution of symptoms, and supports the changes predicted in the UBD model , specifically the relationship between UBD and scapular dyskinesis. The videos below are a good starting point for addressing RSP and UBD with a focus on the structures mentioned in this review.

Brookbush Institute videos

Pectoralis Minor SA Release

Thoracic Spine Mobilization

Pectoralis Minor Manual Stretch

Serratus Anterior Isolated Activation

Serratus Anterior Activation Progressions

Lower Trapezius Isolated MMT

© 2016 Brent Brookbush

Questions, comments, and criticisms are welcomed and encouraged

  1. RESEARCH REVIEW: Wong CK, Coleman D, diPersia V, Song J, Wright D. (2010). The effects of manual treatment on rounded-shoulder posture, and associated muscle strength. Journal of Bodywork & Movement Therapies. 14: 326-333.
  2. Lawrence RL, Braman JP, Laprade RF, Ludewig PM. (2014) Comparison of 3-dimensional shoulder complex kinematics in individuals with and without shoulder pain, part 1: sternoclavicular, acromioclavicular, and scapulothoracic joints. 44(9): 636-645.
  3. Finley MA, Lee RY. (2003). Effect of sitting posture on 3-dimensional scapular kinematics measured by skin-mounted electromagnetic tracking sensors. Phys. Med. Rehabil. 84: 563-568.
  4. Wang CH, McClute P, Pratt NE, Nobilini R. (1999). Stretching and strengthening exercises: their effect on three-dimensional scapular kinematics. Arch Phys Med Rehabil. 80(8): 923-929.
  5. Gumina S, Di Giorgio G, Postacchini F, Postacchini R. (2008). Subacromial space in adult patients with thoracic hyperkyphosis and in healthy volunteers. Chir Organi Mov. 91:93-96.
  6. Lee, J, Cynn H, Yoon T, Ko C, Choi W, et al. (2015). The effect of scapular posterior tilt exercise, pectoralis minor stretching, and shoulder brace on scapular alignment and muscles activity in subjects with round-shoulder posture. Journal of Electromyography and Kinesiology. 25:107-114.