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Tuesday, June 6, 2023

Altered Neuromuscular Activity of the Serratus Anterior in Individuals with Neck Pain

Brent Brookbush

Brent Brookbush


Research Review: Altered Neuromuscular Activity of the Serratus Anterior in Individuals with Neck Pain

By Jinny McGivern DPT, PT, Certified Yoga Instructor

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

Original Citation: Helgadottir, H., Kristjansson, E., Einarsson, E., Karduna, A., & Jonsson, H. (2011). Altered activity of the serratus anterior during unilateral arm elevation in patients with cervical disorders. Journal of electromyography and kinesiology,21(6), 947-953. ABSTRACT

Notice the different bundles of fibers - www.exrx.net
Caption: Notice the different bundles of fibers - www.exrx.net

Notice the different bundles of fibers - www.exrx.net

Why is this relevant?: In our current digital age with perpetual smartphone, tablet and computer use, neck pain is a common occurrence in adult populations. The connection between the function of the scapula and cervical spine is often under-appreciated. This research provides essential information on the behavior of the serratus anterior, the primary stabilizer of the scapula , during arm elevation in individuals with and without neck pain.

Study Summary

Study Design Descriptive Study
Level of Evidence VI - Evidence from a single descriptive or qualitative study
Subject Demographics
  • This study considered the behavior of the serratus anterior (SA) and 3 parts of the Trapezius (TP) during arm elevation in 3 groups: Asymptomatic controls (AC), individuals with insidious onset of neck pain (IONP), and individuals with whiplash associated disorders (WAD).

  • Age: AC 30 yrs +/- 8; IONP 35 yrs +/- 8; 33 yrs +/- 10.
  • Gender: AC 18 women/5 men; IONP 20 women/2 men; WAD 24 women/3 men).
  • Characteristics:
    • All participants were right handed. All individuals with neck pain had received some type of PT prior to participation in study.
    • AC reported no history of neck or shoulder dysfunction. AC members were matched to the subjects in the symptomatic groups with respect to height, weight, age, gender and physical activity level.
    • IONP group reported no history of whiplash injury or MVA.
    • WAD group consisted of individuals with a history of neck pain related to motor vehicle accident (MVA) with loss of neck range of motion (ROM) and point tenderness. Subjects reported no neck pain prior to MVA.

  • Inclusion Criteria:
    • IONP & WAD groups: Age 18-55; Score of at least 10 on the Neck Disability Index (NDI); Neck symptoms lasting more than 6 months.
    • AC group: No history of neck or shoulder dysfunction.

  • Exclusion Criteria: For all groups: any known pathology of the shoulder joint; history of head injury or spinal fractures; systemic pathology; serious psychological condition
Outcome Measures
  • Location of symptoms via body chart
  • Average Pain intensity over the last 7 days via a 10 cm Visual Analog Scale (VAS) (0 = no pain; 10 = worst pain ever)
  • Disability level via self reported questionnaire (NDI)
  • Onset of muscle activation of serratus anterior, upper, middle & lower trapezius at start of movement
  • Duration of muscle activity of serratus anterior, upper, middle & lower trapezius during ascent/descent
  • No significant difference between the 3 groups for age, weight or height
  • Symptom distribution: 26 subjects with bilateral symptoms (13 IONP, 13 WAD); 10 with right sided symptoms (4 IONP, 6 WAD); 13 with left sided symptoms (5 IONP, 8 WAD).
  • WAD group reported significantly higher pain than IONP group (6 cm +/- 2 versus 4.8 cm +/- 1) .
  • WAD group reported significantly higher Disability levels on the NDI than the IONP group (38 +/- 18 versus 29 +/- 10).
  • There was a main effect for onset of muscle activation of the serratus anterior among the groups.
    • Serratus anterior demonstrated a significantly delayed onset of muscle activation in both the IONP and WAD groups as compared to AC.  There was no statistically significant difference between the symptomatic groups.

  • There was a main effect for duration of muscle activity of the serratus anterior among the groups.
    • Serratus anterior demonstrated a significantly shorter duration of muscle activation in both the IONP and WAD groups as compared to AC.  There was no statistically significant difference between the symptomatic groups.

  • There were no main effects or interactions between the groups for the upper, middle or lower trapezius onset or duration of activity.
  • There was a weak correlation (<.3) between EMG onset and duration of muscle activity with NDI and VAS scores.
ConclusionsThis research provides evidence of a link between neuromuscular activity of the serratus anterior and function of the cervical spine.
Conclusions of the ResearchersIndividuals with IONP and WAD demonstrated significantly delayed onset and reduced duration of serratus anterior activity bilaterally during arm elevation.  It is possible that changes are related to a central response to chronic pain as location of neck symptoms did not affect location of serratus anterior activity alterations.  This research did not observe altered neuromuscular activity of the upper, middle and lower trapezius between groups.

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Review & Commentary:

There were many strong methodological components to this research, particularly in how the authors organized their sample. Medical histories were taken and individuals with traumatic versus insidious mechanisms of injury were sorted into different groups. This allowed the researchers to observe the role that the mechanism of injury might play in regards to neuromuscular changes of the serratus anterior and/or trapezius . It also controlled for a potentially confounding variables. After a history was taken, one of the researchers examined each subject's neck & shoulders in order to determine that the shoulder joint was not contributing to dysfunction (and that the neck was dysfunction free in the AC group). The authors did not rely on an absence of pain as confirmation of the absence of dysfunction. From a procedural point of view, the authors collected both EMG and kinematic data which allows for a better understanding of how neuromuscular activity correlates with movement. Recommended procedures were followed for surface electrode placements. Standardization measures were taken to ensure uniform performance of the elevation task among subjects. A vertical surface was used to maintain consistent performance of upper extremity elevation in the scapular plane (30 degrees anterior to frontal plane) and the tempo of movement was regulated with a metronome.

One of the primary limitations of this research, which the authors acknowledge, was the use of surface electrodes for EMG recordings of the 3 parts of the trapezius and serratus anterior. Surface EMG electrodes are subject to error, due to potential cross talk from neighboring muscles. However, the authors point out that for larger muscles, such as those observed in this study, needle EMG would only provide information about the activity of the motor units within a small area, rather than an overall picture of muscle activity. That said, it was reported that the electrodes for the serratus anterior were placed over ribs 6-8. It possible that the data collected on this muscle may only correlate with the lower portions of it (although no study to our knowledge has shown that the serratus anterior may be segmentally recruited). Data was collected during only 1 raising and lowering of the arm (after EMG & kinematic analysis synced). It may have been beneficial to have taken the average of several arm motions to improve the accuracy of the findings. With respect to the sample, the researchers point out that the study included more women than men, therefore may have limited generalizability. They stated that men tended to have concurrent shoulder dysfunction which excluded them from participation in this study. Finally, the researchers did not comment on whether or not their subjects demonstrated any radicular symptoms into the upper extremity. Future research should examine whether the presence of radicular symptoms alters the onset & duration of muscle activity of the muscles of the shoulder girdle.

Why is this study important?

This study provides evidence of a link between cervical spine pain and shoulder girdle function . It opens the door for future research studies to determine the efficacy of interventions involving training of the serratus anterior on reducing neck pain.

How does it affect practice?

This study provides valuable information on the behavior of the serratus anterior muscle during upper extremity elevation in individuals who have optimal shoulder motion, but suffer from cervical dysfunction or pain. Although this study does not carry the weight of an intervention study in providing practical applications, it does encourage the human movement professional to consider scapular stability and the function of serratus anterior in clients, especially those reporting neck pain or who may have a history of neck pain. In those with neck pain in their past, it is possible that although the pain may have abated, optimal function of the serratus anterior may not have returned. This could potentially set the stage for future episodes of neck or shoulder pain. In regard to patient education, this study provides valuable information that can be shared with clients about how different regions of the body are inter-related.

How does it relate to Brookbush Institute Content?

This research supports the Upper Body Dysfunction (UBD) predictive model of postural dysfunction as described by the Brookbush Institute. The UBD model considers the serratus anterior as a muscle with a propensity to become long and under-active. This study indicates that this is indeed the case in individuals with neck pain, even though shoulder function appears optimal shoulder. The Brookbush Institute advocates addressing the serratus anterior with activation and integration techniques. In the context of a corrective exercise routine, these activities would follow inhibitory techniques (release, lengthen, mobilize) for the short & overactive antagonists such as the levator scapula, rhomboids , pectoralis minor, etc. Below are a series of videos describing isolated activation techniques with progressions, as well as reactive activation techniques to train the serratus anterior to function in compound movement patterns with appropriate timing.

Serratus Anterior Isolated Activation

Serratus Anterior Activation Progressions

Serratus Anterior Reactive Activation

© 2014 Brent Brookbush

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