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Tuesday, June 6, 2023

Altered trapezius recruitment pattern in individuals with subacromial impingement

Brent Brookbush

Brent Brookbush


Research Review: Altered trapezius recruitment pattern in individuals with subacromial impingement

By Stefanie DiCarrado DPT, PT, NASM CPT & CES

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

Original Citation: Cools, A.M., Witvrouw, E.E., Declercq, G.A., Danneels, L.A., Cambier, D.C. (2003) Scapular muscle recruitment patterns: Trapezius muscle latency with and without impingement symptoms. The American Journal of Sports Medicine 31(4). 542-549 - ABSTRACT

The trapezius muscle is a superifical muscle with 3 different "segments" - upper, middle, and lower. All three assist with scapular upward rotation but differ in their ability to elevate, retract, and depress the scapula (respectively).

Why is this relevant?: Chronic shoulder pain due to subacromial impingement syndrome (SIS) is considered one of the most common dysfunctions among overhead athletes (1,2,3). This population is most susceptible to SIS as repetitive compression and subsequent irritation of the supraspinatus tendon, subacromial bursa, and long head of the biceps tendon can occur with arm elevation. Proper glenohumeral (GH) and scapulothoracic (ST) mechanics are necessary to reduce, eliminate, and prevent SIS (4,5). This indicates the need to understand both arthokinematics and osteokinematics as well as the muscles that impose forces across both joints.

Study Summary

Study DesignProspective Cohort Study
Level of EvidenceIIa: Evidence from at least one controlled study without randomization
Subject Demographics
  • Age:
    • SIS Group: 25.9 yrs (mean)
    • Controls (CON): 22.4 yrs (mean)

  • Gender:
    • SIS Group: 26 males, 13 females
    • CON: 19 males, 11 females

  • Characteristics: overhead athletes from a variety of sports (swimming, tennis, volleyball, other)
  • Inclusion Criteria:  at least 2/5 of the following: + Neer, + Hawkins Kennedy, + Jobe's (Empty Can), + Apprehension & + Jobe's Relocation
  • Exclusion Criteria: history of shoulder dislocation or surgery, current cervical spine related symptoms or exiting structural injuries within the shoulder complex
Outcome Measures
  • SIS Group
    • Painful vs non painful side: Longer relative latency in LT on the painful side
    • Non painful side: Longer relative latency in UT, MT, LT
      • Significant difference found only between UT, & LT

    • Painful side: Significant differences in UT, MT, LT latency (with respective recruitment order) & all had significantly longer relative latency

  • CON Group
    • Dominant vs non dominant side: longer relative latency in MT on non dominant side
    • Non dominant side: significant differences in onset of MD vs UT, MT, LT without significant difference among the trapezius sections
    • Dominant: significant differences between MD onset and UT & LT onset; no significant difference between MD onset and MT onset; significant differences between onset of  MT & LT

  • SIS Group vs CON Group
    • Painful vs dominant side: significantly longer latency in MT & LT in SIS.
    • Non painful vs non dominant: significantly longer latency in  MT & LT in SIS.

ConclusionsAltered recruitment strategies existed in individuals with SIS, specifically that of increased latency of the scapular stabilizers MT & LT.  Further research is needed to fully explore and understand the cause and effect relationship between altered muscle onset timings and arthrokinematic dysfunction and pain.
Conclusions of the ResearchersOverhead athletes with SIS demonstrated increased onset latency of the LT therefore supporting previous research indicating the relationship between SIS and altered muscle recruitment patterns.  Future research will help determine if the increased latency caused SIS or if the SIS caused the increased latency.

Dr. Brookbush applies Kinesiology Tape to the Lower Trapezius
Caption: Dr. Brookbush applies Kinesiology Tape to the Lower Trapezius

Lower Trapezius Taping

Review & Commentary:

This study provides strong evidence that altered recruitment patterns of scapular stabilizers exist in overhead athletes with subacromial impingement syndrome (SIS). One of the strongest components of this study was the use of each subject as their own control, in addition to having a separate control group. Researchers collected bilateral shoulder EMG and movement data to compare painful to non-painful sides, dominant to non-dominant sides, painful to dominant sides, and non-painful to non-dominant sides. This allowed for comparison of multiple variables within a single study.

The experiment consisted of individuals with unilateral SIS and subjects without impingement attempting to stop an unexpected dropping of the arm from 90° of abduction. The authors described the equipment used, body positioning, and EMG surface electrode placement well enough for future replication. The authors compared each individual muscle EMG data during the experiment to the maximum voluntary contraction (MVC) for each muscle measured prior to testing. The authors used typical manual muscle test positions to obtain the MVC but in cases where non traditional positions were used, they described the position and provided a citation for reference and validation. Special care was taken to "blind" the subjects to any clues of the arm dropping by having them wear masks and headphones.

The non dominant or non injured side was tested first. Both groups were familiarized with the procedure before testing. Researchers defined muscle latency response as "the period between the start of the tilting of the goniometer and the beginning of muscle activity" and a muscle contraction as EMG data at least 10% of the MVC beyond baseline activity levels (pg 545). The difference between the trapezius muscle onset time and that of the MD was referred to as relative muscle latency. In addition to onset timings and comparisons between the trapezius and the MD; the temporal recruitment order for the different segments of the trapezius muscle were compared.

Interesting, within this study, the SIS group demonstrated bilateral delayed onset of scapular stabilizers MT & LT  after the initiation of motion as compared to the control group. Additionally, the SIS group had longer relative latencies than the controls. Within the control group, only the dominant arm displayed non significant differences in MD and MT  onset timing.

It is not surprising that an altered recruitment pattern existed in a painful shoulder, but altered patterns bilaterally is interesting. Could this mean the altered recruitment pattern led to SIS within the experimental group? The authors were unable to answer this question definitively and stated further research is required. They postulated that the dominant arm in the healthy controls did not demonstrate significant relative latency because the athletes had trained their arm through their sport to stabilize correctly. However, there are still many questions remaining: Why were some of the athletes able to do this and others weren't? Did they have better trainers? Better structural integrity?

This study is not without limitations. As discussed by the authors, the use of surface electrodes always brings with it the risk of cross talk between muscles. However, the trapezius being a large and superficial muscle would not have posed much cross talk risk. The middle deltoid is small but also very superficial and easy to target via surface electrode. Any study could benefit from a larger sample size but the study consisted of a fair number of subjects and provided statistically significant data. Although not truly a limitation since the focus of the study was the trapezius muscle latency, it would have been interesting to collect data from all scapular stabilizers during unexpected motion as the serratus anterior has a tendency for inhibition in upper extremity dysfunction.

Why is this study important?

This study is important because it explores the capacity of the entire trapezius muscle to assist in stabilizing the scapula immediately following unexpected upper extremity motion. This is the body's ability to control movement instead of create movement. At the time of publication, the authors were unaware of any other study looking at eccentric control of unexpected, fast movement. Previous research indicated shoulders with GH instability or SIS have altered muscle activity levels in the UT & LT  and serratus anterior with volitional, controlled movement (6,7,8,9,10). The current study found altered activity of the UT, MT, & LT  with uncontrolled movement of the upper extremity in shoulders with SIS.

How does it affect practice?

It is important for clinicians to recognize proper scapular position and implement verbal or manual cues to improve the inter-muscular coordination between stabilizers and prime movers during movement patterns. Decreased recruitment patterns lead to compensatory patterns, movement dysfunction, and eventually, pain or injury. This is the basis of the Brookbush Institutes predictive model of Upper Body Dysfunction (UBD) and is discussed further in the next section.

How does it relate to Brookbush Institute Content?

The Brookbush Institute's predictive model of UBD builds upon and enhances previously established postural dysfunction/movement impairment models. The UT  is a tricky muscle that seems capable of altered activity patterns that result in over-activy or under-activity (This is not common, as most muscles have a propensity to adopt one or the other). Traditional models describe the scapula within this dysfunction as being elevated and protracted but the Brookbush Institute proposes a different viewpoint: that the scapula is actually anteriorly tipped and downwardly rotated causing a "pseudo elevation" of the superior angle. A key component of SIS may be a lack of upward rotation, and excessive anterior tipping - both of which decrease subacromial space (4,5). When analyzing dysfunction, we must "do our math" to establish which muscles to inhibit and which to activate. In the scenario of a downwardly rotated scapula, we have overactivity in the: levator scapula, rhomboids , pectoralis minor and under-activity in our upward rotators: serratus anterior and UT & LT . . Further, the UT , levator scapula, and pectoralis minor may be overactive in an anteriorly tipped scapula with concurrent under-activity in the LT  and serratus anterior. This study provides some evidence of the characterization of the UT and LT in the UBD model.

One must consider the ability of a muscle to control motion, not only the ability to create it. The UT & LT  assist with upward rotation and help to control downward rotation; the MT  not only retracts the scapula but helps maintain congruence of the scapula to rib cage, and the LT  helps control and limit anterior tipping to also maintain congruence with the rib cage. Proper strength and activation timing of the trapezius is important to prevent impingement of subacromial structures (4,5).

This particular study, as mentioned previously, focused on the muscles ability to stop an unpredictable motion. This would require eccentric control to slow the movement followed by isometric stabilization to hold the limb in a new position. "Reactive activation" aims to increase the firing rate of targeted muscles to control osteokinematic and arthorkinematic motion. The following videos demonstrate lower trapezius activation (The Cobra Exercise) as well as reactive activation of all scapula and GH stabilizers. Note: all of the commonly used "reactive activation" exercises for commonly under-active upper body muscles are included, as these exercises are "less isolated" and the use of anyone of these exercises may improve recruitment and timing for any one of the under-active structures.

Trapezius Isolated Activation

Prone Floor Cobra (and Chest-out/Thumbs-out)

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

Standing Cobra

Standing Cobra to Balance to Calf Raise

Trapezius Reactive Activation

Serratus Anterior Reactive Activation

External Rotator Reactive Integration


1. Almekinders LC: Impingement syndrome. Clin Sports Med 20: 491–504, 2001

2. McMaster WC, Troup J: A survey of interfering shoulder pain in United States competitive swimmers. Am J Sports Med 21: 67–70, 1993

3. Pink MM, Tibone JE: The painful shoulder in the swimming athlete. Orthop Clin North Am 31: 247–261, 2000

4. Lawrence, R. L., Braman, J. P., Laprade, R. F., & Ludewig, P. M. (2014). Comparison of 3-dimensional shoulder complex kinematics in individuals with and without shoulder pain, part 1: sternoclavicular, acromioclavicular, and scapulothoracic joints . journal of orthopaedic & sports physical therapy, 44(9), 636-A8.

5. Lawrence, R.L., Braman, J.P., Staker, J.L., Laprade, R.F., Ludewig, P.M. (2014) Comparison of 3-dimensional shoulder complex kinematics in individuals with and without shoulder pain, Part 2: Glenohumeral joint. Journal of Orthopaedic & Sports Physical Therapy 44(9). 646-B3

6. Bagg SD, Forrest WJ: Electromyographic study of the scapular rotators during arm abduction in the scapular plane. Am J Phys Med 65: 111–124, 1986

7. Ludewig PM, Cook TM, Nawoczenski DA: Three-dimensional scapular orientation and muscle activity at selected positions of humeral elevation. J Orthop Sports Phys Ther 24: 57–65, 1996

8. Moseley JB Jr, Jobe FW, Pink M, et al: EMG analysis of the scapular muscles during a shoulder rehabilitation program. Am J Sports Med 20: 128–134, 1992

9. Glousman R, Jobe F, Tibone J, et al: Dynamic electromyographic analysis of the throwing shoulder with glenohumeral instability. J Bone Joint Surg 70A: 220-226, 1988

10. McMahon PJ, Jobe FW, Pink MM, et al: Comparative electromyographic analysis of shoulder muscles during planar motions: Anterior glenohu- meral instability versus normal. J Shoulder Elbow Surg 5: 118–123, 1996

© 2014 Brent Brookbush

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