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Tuesday, June 6, 2023

Upper Extremity Kinematics Impacted by Scapula Muscle Fatigue

Brent Brookbush

Brent Brookbush


Research Review: Upper Extremity Kinematics Impacted by Scapula Muscle Fatigue

By Jinny McGivern, DPT, PT Certified Yoga Instructor

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

Original Citation: Suzuki, H., Swanik, K. A., Huxel, K. C., Kelly, J. D., & Swanik, C. B. (2006). Alterations in upper extremity motion after scapular-muscle fatigue. Journal of Sport Rehabilitation, 15(1), 71. ARTICLE

Image courtesy of http://www.hughston.com/online-courses/online-courses/hha/a_16_1_1.htm

Why is this relevant?:

The scapula is viewed as the most proximal segment of the upper extremity. If the upper extremity is considered as a "kinetic chain," the link between adjacent segments may be considered as related to one another. This research demonstrates a connection between the scapula and the elbow, two segments that are not directly adjacent to one another, but whose motion affects the performance of the chain as a whole. This research indicates that fatigue in scapula muscles can result in compensations in upper extremity segments distal to the shoulder.

Study Summary

Study Design Descriptive study
Level of Evidence VI - Evidence from a single descriptive study
Subject Demographics

30 individuals (23 for elbow analyses, 26 for shoulder analyses.  The results from a few subjects were excluded due to poor video quality)

  • Age: 21.4 +/- 2.7 years
  • Gender: Male
  • Characteristics: Healthy individuals; All subjects right arm dominant (throwing hand)
  • Inclusion Criteria: n/a
  • Exclusion Criteria: Currently involved in an upper extremity sport (volleyball/baseball); Head, neck, upper back, shoulder, elbow or wrist injuries in the preceding 6 months; history of upper extremity surgery, and/or neuropathology
Outcome MeasuresKinematic data was collected during 3 different phases of a throwing task.Phases were divided as follows:
  • The cocking phase (wind up to max should external rotation)
  • The acceleration phase (time between maximal external rotation and ball release)
  • Follow through (ball release to termination of throwing motion)

The following values were collected during a throw, both before and after a scapular muscle fatigue protocol:

  • Shoulder External Rotation Angle (combined shoulder scapula & trunk motions - cocking phase only)
  • Shoulder Abduction
    • Displacement (degrees)
      •  Minimum
      •  Maximum
      • Total range of motion

    • Velocity (m/s)
      • Maximum (extension)
      • Maximum (flexion)
      • Average

  • Elbow Flexion/Extension 
    • Displacement (degrees)
      • Minimum (flexion)
      • Maximum (extension)
      • Total range of motion

    • Velocity (m/s)
      • Maximum (extension)
      • Maximum (flexion)
      • Average

  • Scapula Upward Rotation in standing (in degrees via digital inclinometer along spine of the scapula at 0, 45 and 90 degrees of shoulder abduction in the scapula plane)
  • Throwing Accuracy (measured via absolute radial error distance from target in cm)
  • No significant differences were found in shoulder abduction or external rotation for either displacement or velocity variables pre- to post-fatigue.
  • Significant differences were found in total elbow range of motion during the cocking phase pre- versus post-fatigue (p<.001).
  • Elbow extension tended to be greater during post fatigue trials, although this was not statistically significant.
  • Significant differences existed between pre & post fatigued conditions for average (p <.001) and maximum (p=.02) elbow flexion velocity during the follow through phase.
  • There was significantly more scapular upward rotation between 0 and 90 degrees of abduction, however there was no significant difference between pre & post fatigue conditions (p=.131).
  • There was a significant decrease in throwing accuracy pre  & post fatigue protocol (p=.01).
ConclusionsScapular muscle fatigue results in altered kinematics in distal portions of the upper extremity.  This indicates a functional interdependence between proximal and distal segments.
Conclusions of the ResearchersScapular muscle function impacts movement at distal joints of the upper extremity. This research demonstrates that scapula muscle fatigue impacts both kinematics at the elbow, as well as accuracy in a throwing task.

Image courtesy of https://www.studyblue.com/online-courses/online-courses/notes/note/n/muscles-upper-limbs/deck/7130755

Review & Commentary:

This research had many strong aspects to its methodology. It examined both the kinematics and accuracy of a challenging functional task, throwing. This provides the reader a perspective of how the upper extremity moves during the throw, as well as a sense of how skill (as defined by ability to hit the target) is affected during performance of the task. In designing the task, the researchers attempted to isolate the role of the upper extremity by having the subjects perform the task while seated. The authors used a motion analysis and video system to record kinematics of the throwing task. Scapula upward rotation was assessed in standing. This particular motion of the scapula was selected for analysis because it has been observed to be impaired in previous research studies investigating both healthy fatigued and pathological populations. The scapular muscle fatiguing protocol was tailored to each subject by establishing a load based on a percentage of their maximal voluntary contraction for scapular elevation, protraction and retraction, as measured with a handheld dynamometer. Scapula fatiguing protocol consisted of a circuit of: shoulder shrugs (70% & 80% MVIC); prone neck extension (manually resisted); scapular push ups (40 beats per minute); prone scapular retractions (70% MVIC); scapula retraction/protraction (manually resisted); prone arm raise to 90 degrees abduction (30% MVIC); prone arm raise to 120 degrees abduction (30% MVIC). Specific criteria was pre-determined for each exercise to demonstrate capacity to induce fatigue. Post fatigue data collection was performed between 30 and 60s after activity was completed.

While this study had many strengths to its design, it also had limitations. The sample size was small for the number of variables considered. No power analysis was performed to determine the number of subjects needed to give statistical significance to the results. 2 cameras and surface markers were utilized as part of the motion analysis system. It would be beneficial if this study could be replicated using an 8-10 camera setup with bone markers for a more comprehensive view of the throwing task. The researchers report that prior to collecting pre-fatigue measurements subjects were directed through an active stretching series for shoulder horizontal abduction/adduction, flexion/extension, elbow flexion/extension and circumduction. It is unknown if any of the subjects had any baseline range of motion deficits in these ranges of motion to warrant a pre-activity stretching protocol. Furthermore, the performance of stretching activities prior to pre-fatigue condition data collection may have impacted the results and the differences noted pre- versus post-fatigue. The researchers assessed upward rotation as a measure of scapula kinematics; however, they did not assess upward rotation strength, nor did the scapula muscle fatiguing protocol specifically target upward rotation as a movement of the scapula. It is possible that this may explain why there was not a statistically significant difference in scapula kinematics for upward rotation pre- versus post-fatigue. Finally, the authors elected to assess "shoulder complex" motion, as opposed to differentiating between scapulothoracic and glenohumeral kinematics. Future research should assess each segment (joint) of the upper extremity individually during a functional task (such as throwing) to provide a more detailed view of the function of the upper extremity.

It was surprising to learn that the elbow demonstrated compensation patterns under scapula fatigued conditions, whereas the shoulder did not. The authors hypothesize that the nature of the scapula fatiguing protocol, or the performance of the throwing task in sitting may have altered how force was translated through the upper extremity. Future research should examine how upper extremity kinematics differ when performing a throwing task in sitting versus standing.

Why is this study important?

This study demonstrates the connection between proximal and distal segments of the upper extremity during an athletic activity such as a throwing task. Furthermore, it demonstrates the importance of scapula muscle endurance. It hints at the fact that "repetitive stress injuries" at distal segments of the upper extremity could possibly be connected to a failure of the dynamic stabilizing musculature of the scapula.

How does it affect practice?

This research encourages the human movement professional to assess the upper extremity as a whole (and potentially the thorax), in addition to a segment by segment assessment of individual joints. This research, in conjunction with other studies reviewed on this site (Ayhan et al., 2015 ; Day et al., 2015 ), demonstrates that well functioning scapula musculature is necessary for a optimal function of the upper extremity. Don't skimp on the scapula stabilization activities at any phase of training or rehabilitation! Additionally, it is important to ensure that scapula muscle endurance is achieved for optimal function during the entire duration of the sport.

How does it relate to Brookbush Institute Content?

The Brookbush Institute's predictive model of postural dysfunction - Upper Body Dysfunction (UBD)  - considers the common compensation pattern noted in joints and muscles spanning from the thoracic and cervical spines and branching-out through the upper extremity. The researchers in the above study grouped serratus anterior , rhomboid major/minor , levatator scapulae , upper, middle and lower trapezius , as well as pectoralis minor all together as "scapula stabilizers." The Brookbush Institute separates these muscles into 3 categories; muscles with a tendency to become short/overactive, long/under-active and long/over-active. Muscles are then addressed with techniques specific to those tendencies to establish more optimal length-tension relationships and activity, allowing the entire system to function more efficiently. For a more detailed breakdown of which muscles tend to fall where see this article on Upper Body Dysfunction (UBD) .

In terms of improving scapula stability and endurance during a throwing task the Brookbush Institute would recommend a combination of mobility techniques (static release, stretching, and self-administered mobilizations) with activation, integration and task specific activities. Below is a series of videos which details how the Brookbush Institute would address the scapula muscles targeted in this study, after a brief discussion of altered length tension relationships.

Altered Length Tension Relationships

Pectoralis Minor SA Static Release

Upper Trap SA Static Release

Levator Scapulae SA Static Release

Pectoralis Major and Minor SA Static Stretch

Upper Trap SA Static Stretch

Levator Scapulae SA Static Stretch

Trapezius Isolated Activation

Serratus Anterior Isolated Activation

Serratus Anterior Activation Progressions

Prone Cobra on Foam Roll (Activation for muscles of the scapula, thorax & deep cervical flexors)

Serratus Anterior Reactive Activation

Trapezius Reactive Activation


Ayhan, C., Camci, E., & Baltaci, G. (2015). Distal radius fractures result in alterations in scapular kinematics: A three-dimensional motion analysis. Clinical Biomechanics.

Day, J. M., Bush, H., Nitz, A. J., & Uhl, T. L. (2015). Scapular Muscle Performance in Individuals With Lateral Epicondylalgia. Journal of Orthopaedic & Sports Physical Therapy, (Early Access), 1-35.

© 2015 Brent Brookbush

Questions, comments, and criticisms are welcomed and encouraged -