The Comparative Effects of Position and Cordless Phone Equipment on Upper Trapezius and Cervical Par

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The Comparative Effects of Position and Cordless
Phone Equipment on Upper Trapezius and Cervical
Paraspinal Surface EMG

• Fred Shaffer, Ph.D., Logan Banks, Adam Lipps,
  Frederick Franken, Lynn Giddings, Ashley Burden,
  and Jennifer Schwyhart
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• Truman State University
•  

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Introduction

• Shaffer, Malone, Sippely, and Callahan (2000)
  examined the effects of three book bag conditions
  (backpack, shoulder bag-same side, and shoulder
  bag-opposite side) on upper trapezius and
  cervical paraspinal sEMG

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Introduction
Backpack
Shoulder-bag same-side
Shoulder-bag opposite-side
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Introduction

• The shoulder bag-same side condition produced
  higher preferred-shoulder sEMG levels and sEMG
  asymmetry than the initial baseline, opposite
  side, or backpack conditions

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Purpose

• Holding a cordless phone against the ear might
  recruit upper trapezius and cervical paraspinal
  muscles on that side to stabilize the phone
• This could produce sEMG asymmetry in these
  muscles, like that produced by a single-strap
  book bag worn on the same side

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Purpose

• Since talking with a headset eliminates the need
  to hold the phone because it is attached to
  clothing, sEMG asymmetry should be significantly
  lower

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Purpose

• We examined the effects of position (sitting or
  standing) and equipment (phone or headset) on
  upper trapezius and cervical paraspinal sEMG
• This study has clinical relevance because chronic
  muscle over-use can produce myofascial pain
  (Cram, 1990)

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Participants

• Forty-three undergraduate students (9 men and 34
  women)
• Ages ranged from 18 to 23 years
• Participants volunteered for academic credit

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Apparatus

• A J J I-330 Physiological Monitoring System
  measured sEMG using
• M-501 module (25-1000 Hz bandpass)
• 10-mm silver/silver-chloride surface
  electrodes placed over the upper trapezius
  and cervical paraspinal muscles

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Apparatus

• Active electrodes separately monitored left and
  right upper trapezius muscles and left and right
  cervical paraspinal muscles as described by Cram
  (1990)
• Skin-electrode impedance was maintained under 20
  Kohms and within 5 Kohms for each
  active-reference pair

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Apparatus

• Phone equipment included
• Panasonic 2.4 GHz cordless phone, which weighs
  240.97 g and can be attached by its belt clip
• Plantronics headset (model 1-01 M145), which
  features a speaker that fits inside one ear and a
  microphone on an integrated arm

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Apparatus
Phone
Headset
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Procedure

• Participants stabilized for 15 min in a 23.9 oC
  room
• The left and right upper trapezius muscles and
  left and right cervical paraspinal muscles were
  monitored throughout this experiment with eyes
  open

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Trapezius placement

• The active electrodes were centered between C7
  and the angle of the acromion

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Cervical paraspinal placement
The active electrodes were placed ½ inch lateral
to the spine over the muscle belly at C4
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Procedure

• The two within-subjects variables were position
  (sitting or standing) and equipment (cordless
  phone or headset)
• Participants were randomly assigned using a
  balanced Latin square to five, 5-minute treatment
  conditions, separated by 3-minute buffer periods

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Procedure

• These conditions included baseline,
  sitting-phone, sitting-headset, standing-phone,
  and standing-headset
• During the remaining four conditions,
  participants completed actual phone conversations
  on the same general topic with the same
  individual

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Procedure

• In the sitting-phone condition, subjects
  conversed while sitting upright and holding the
  phone on their preferred side
• In the sitting-headset condition, subjects
  conversed while sitting upright and using the
  headset on their preferred side

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Procedure

• In the standing-phone condition, subjects
  conversed while standing and holding the phone
  on their preferred side
• In the standing-headset condition, subjects
  conversed while standing and using the headset on
  their preferred side

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Statistical analysis

• We normalized sEMG values using a natural
  logarithmic transformation
• We analyzed trapezius and cervical paraspinal
  asymmetry measurements using a General Linear
  Model Repeated Measures procedure with a
  Greenhouse-Geisser correction when sphericity
  could not be assumed

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Statistical analysis

• We calculated eta2 (h2) to measure the proportion
  of variability in the dependent variable
  explained by the independent variable
• eta2 indexes the strength of the relationship
  between the independent and dependent variables
  and ranges from 0 - 1

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Results Position

• Trapezius asymmetry was significantly greater
  when conversing during standing than sitting,
  F(1, 42) 30.18, p .0001, h2 .42
• Position did not significantly affect cervical
  paraspinal sEMG asymmetry

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Results Equipment

• Talking on a cordless phone resulted in
  significantly higher trapezius sEMG asymmetry
  than conversing on a headset, F(1, 42) 22.65, p
  .0001, h2 .35

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Trapezius sEMG asymmetry in microvolts RMS
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Trapezius sEMG asymmetry in microvolts RMS

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Results Equipment

• Talking on a cordless phone also resulted in
  significantly higher cervical paraspinal sEMG
  asymmetry than conversing on a headset, F(1, 42)
  9.91, p .00013, h2 .19

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Cervical paraspinal sEMG asymmetry in microvolts
RMS
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Cervical paraspinal sEMG asymmetry in microvolts
RMS

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Discussion

• Position and equipment independently influenced
  trapezius sEMG asymmetry
• Asymmetry was greater while standing than sitting
  during a cordless phone conversation and when
  using a phone instead of a headset

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Discussion

• Equipment also affected cervical paraspinal sEMG
  asymmetry
• Asymmetry was greater when using a cordless phone
  instead of a headset

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Discussion

• The sEMG asymmetry produced when holding a phone
  to the ear resembles the pattern Shaffer et al.
  (2000) observed with a single-strap book bag
  worn on the same side

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Discussion

• We recommend that future researchers study older
  subjects and obtain comparable numbers of men and
  women to investigate the generality of these
  findings

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Discussion

• This study should be replicated with cellular
  phones, which are typically lighter, to see if
  position and equipment also produce trapezius and
  cervical paraspinal sEMG asymmetry when using
  these devices

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Discussion

• These findings support the recommendation that
  consumers should sit and use headsets during
  cordless phone conversations to minimize
  trapezius and cervical paraspinal sEMG imbalance

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Discussion

• These precautions might help individuals who
  extensively use cordless phones to reduce the
  incidence and severity of myofascial pain due to
  prolonged muscle contraction

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The Truman State University Research Team