An  Introduction  to  Electromyography    

Background  Material:  

A   muscle   is   an   organized   collection   of   muscle   fibers,   which,   in   turn,   are   comprised   of   groups   of  components   known   as   myofibrils.     In   the   musculo-­‐skeletal   system,   nerve   fibers   initiate   electrical  impulses   in   the  muscle   fibers  known  as  muscle  action  potentials.    They  produce  chemical   interactions  which  activate  shortening  of  the  myofibrils.    The  more  activated  fibers  in  a  muscle  unit,  the  stronger  the  contraction  that  the  unit  can  generate.    Muscles  can  only  exert  force  by  pulling  as  they  shorten.    Push  and   pull   forces   in   the   musculoskeletal   system   are   generated   by   pairing   of   muscles   that   act   in   an  antagonistic  fashion  –  one  muscle  contracts  while  a  complementary  muscle  relaxes.    

 

 

 

 

 

 

 

 

 

 

Figure  1:  Microscopic  image  of  muscle  fiber  http://classes.midlandstech.edu/carterp/Courses/bio210/chap09/Slide8.JPG  

 

Figure   2:     Constituents   of   a   muscle      http://www.strength-­‐and-­‐power-­‐for-­‐volleyball.com/images/volleyball-­‐genetics-­‐muscle-­‐fiber-­‐2.jpg  

 

  An  Introduction  to  Electromyography    

A  non-­‐invasive  technique  used  to  assess  the  interactions  of  muscle  fibers  and  to  evaluate  the  underlying  muscular   activity   that   is   generated  when  a  physical  motion   transpires   is   known  as   electromyography.  Electromyography   is   utilized   in   many   fields   including   fitness,   sports,   and   clinical   diagnostics.   It   has  become  a  significant   tool   for  categorizing  muscle  performance   in  numerous  muscular  pathologies.    By  measuring  the  number  and  magnitude  of  the  impulses  produced  during  muscle  activation,  it  is  possible  to  assess  how  much  the  muscle  unit  is  being  stimulated  to  yield  a  particular  force.    An  electromyogram  (EMG)  is  the  visual  illustration  of  the  signals  generated  during  muscle  activity.  

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Figure  3:  Electromyography  being  utilized  in  a  clinical  setting  http://www.virtualmedicalcentre.com/uploads/VMC/PageImages/1822_NCS-­‐EMG.jpg  

 

Figure  2:  EMG  Signals  produced  during  an  intentional  movement.    A)  Effort  of  movement,  B)  Processed  EMG  signals  to  show  relationship  to  muscular  effort,  C)  Raw  EMG  signal.  

A  

B  

C  

  An  Introduction  to  Electromyography    

In  this  lab,  electromyogram  (EMG)  signals  will  be  collected  from  two  antagonistic  muscle  units,  the  biceps  and  triceps.    The  EMG  signals  will  enable  assessment  of  the  force  generated  by  these  muscles  during  bicep  flexion  and  relaxation  when  supporting  two  different  weights.    In  addition,  the  signals  will  emphasize  the  antagonistic  interaction  between  these  muscle  groups.  

 A  wireless  data  acquisition  unit  will  be  used  to  simultaneously  record  and  transmit  the  EMG  signals  from  a  set  of  strategically  located  surface  electrodes  to  a  computer  for  display  and  analysis.      

 

Figure  5:  Image  of  biceps  and  triceps,  emphasizing  concept  of  antagonistic  pairs.  

http://4.bp.blogspot.com/_u2tlmyCsos4/TS4v4mDamdI/AAAAAAAAABE/FQF7uhUsLgg/s1600/92940-­‐034-­‐684F9679.jpg  

 

Figure  6:  Block  diagram  of  signal  and  data  path  

 

  An  Introduction  to  Electromyography    

Overview  of  the  Experiment:  

You  will  work  in  pairs.    One  person  will  be  the  source  of  the  EMG  signals.    The  other  person  will  be  operating  the  KinetiSense  software  that  will  record  and  display  the  EMG  signals.    The  activities  that  will  be  conducted  are:  

• Observe  muscle  fiber  activation  by  performing  simple  weight  lifting  exercises  while  recording  muscle  action  potentials  from  electrodes  placed  over  muscles  of  interest.    

• Observe  the  coordination  of  muscle  fiber  activation  originating  from  the  biceps  and  triceps  when  performing  each  activity  

• Observe  the  difference  in  muscle  fiber  activation  when  manipulating  different  weights    

Procedure:  

1. Identify  the  Biceps  and  Triceps  in  the  arm;  flexing  will  help  show  these  two  muscles.    2. Prepare  the  upper  arm  by  wiping  it  with  an  alcohol  pad.  (Allow  ample  drying  time  for  the  alcohol  

so  that  it  will  not  impact  the  adhesive  properties  of  the  electrodes.)    3. Place  two  disposable  EMG  electrodes  on  the  bulk  of  both  the  Biceps  and  Triceps  as  shown  in  

Figure  7.    If  you  are  having  trouble  placing  your  electrodes,  ask  for  assistance,  as  the  entire  exercise  depends  on  the  electrodes  being  properly  placed.  Place  the  remaining  electrode,  which  will  serve  as  ground,  on  your  elbow  for  a  total  of  5  electrodes  

         

 

Figure  7a:  Bicep  electrode  placement   Figure  7b:  Triceps  electrode  placement  

Figure  7c:  Ground  electrode  placement  

  An  Introduction  to  Electromyography    

4. Place  the  supplied  Velco  strap  around  your  waist.    This  will  be  used  to  hold  the  Kinetisense  Command  Module.      

5. Carefully  untangle  and  separate  the  EMG  electrode  leads.    The  blue  leads  will  be  placed  on  the  bicep  electrodes,  the  yellow  leads  on  the  triceps,  and  the  green  lead  on  ground.    Note  that  the  color  in  question  is  the  color  of  the  tape  attached  to  the  wires,  not  the  connectors.      

6. Plug  the  leads  into  the  correct  sockets  in  the  5  port  EMG  cable.    Connect  the  5  port  EMG  cable  to  the  Command  module.  Securely  attach  the  Command  module  to  the  Velcro  belt.    Tuck  the  EMG  cable  into  the  belt  as  well.    Suggestion:  Place  command  module  on  back  side  of  test  subject  to  ensure  that  cables  do  not  interfere  with  motion.    

   

7. Familiarize  yourselves  with  the  Kinetisense  software  by  moving  your  arm  around  and  observing  the  recorded  EMG  signals.      

a. Select  the  Collect  Data  button  on  the  left  sidebar  of  the  KinetiSense  display  b. Select  the  start  button  at  the  top  of  the  screen  

 

 

 

 

 

 

 

Figure  8:  Electrode  lead  and  command  module  placement  

 

  An  Introduction  to  Electromyography    

 

 

 

 

 

 

 

 

 

Data  Collection  Software  Adjustments:  

1. If  you  want  to  change  the  y-­‐axis  of  the  two  graphs,  the  following  process  can  be  taken:    a. Access  the  “Collect  Data”  Screen  b. Right  click  on  the  graph,  and  select  the  Y-­‐axis  choice  c. Select  the  Set  Min/Max  option  

 

Exercise  1:  Bicep  Curl  

2. Observe  and  collect  data  for  the  flexion  and  relaxation  of  the  arm  as  shown  in  Figure  9  with:  • No  external  weight  • 5  pound  weight  • 10  pound  weight      

Make  sure  to  record  enough  data  to  capture  a  full  episode  of  the  flexion  and  relaxation  cycle.    Start  with  the  weight  in  your  hand  and  your  forearm  lying  on  the  table.    Go  through  elbow  flexion  by  raising  the  weight  off  the  table  while  keeping  your  elbow  planted.    You  should  observe  a  display  similar  to  that  shown  in  Figure  10  

a. When  you  are  ready  to  begin  recording  data,  follow  this  sequence:  • Press  “Start”  button  • Press  “Save  Data”  button  (example:  Bicep-­‐5lb)  

b. Perform  3  repetitions  of  this  movement  with  no  external  weight  c. Press  "Stop  Saving  Data”  button  d. Repeat  steps  a,  b,  and  c  with  the  5  and  10  pound  weights  

 

c. Observe  the  changes  in  the  plots  as  you  flex  and  extend  your  arm  (red  line=triceps,  blue  line=biceps).      

d. Using  the  10lb  weight,  do  a  few  bicep  curls,  noting  the  maximum  value  of  the  EMG  signal.    Set  an  appropriate  y-­‐axis  based  on  this  value.    

 

  An  Introduction  to  Electromyography    

     

             Figure  9a:  Bicep  Curl  Start  position         Figure  9b:  Bicep  Curl  Finish  position  

 

 

Figure  10  -­‐  Representative  EMG  signal  plot,  bottom  image  showcasing  bicep  muscle  activity  

 

 

 

 

 

  An  Introduction  to  Electromyography    

Exercise  2:  Triceps  Extension  

3. For  the  Triceps  extension,  do  a  simple  “kickback”  maneuver  as  shown  in  Figure  .  • Stand  about  1-­‐1.5  feet  away  from  the  lab  table.      • Place  your  supporting  hand  flat  on  the  surface  and  pick  up  the  appropriate  weight  with  arm  

you  are  recording  the  EMG  signals  from.      • Let  the  weight  drop  down  and  hang  loosely  in  your  hand.      • Raise  the  weight  until  it  is  level  with  your  hip  then  fully  extend  your  arm  backwards.  • You  should  observe  a  display  similar  to  that  shown  in  Error!  Reference  source  not  found.12.  

 a. When  you  are  ready  to  begin  recording  data,  follow  this  sequence:  

• Press  “Start”  button  • Press  “Save  Data”  button  (example:  Tricep-­‐5lb)  

b. Perform  3  repetitions  of  this  movement  with  no  external  weight  c. Press  “Stop  Saving  Data”  button  d. Repeat  steps  a,  b,  and  c  with  the  5  and  10  pound  weights    

     

 

 

 

Figure  11b:  Kickback  extension  Figure  11a:  Kickback  start  position  

  An  Introduction  to  Electromyography    

 

Figure  11  -­‐  Representative  EMG  signal  plot,  top  image  showcasing  triceps  activity  

 

Viewing  Saved  Data:  

1. On  the  left  side  of  the  Kinetisense  screen,  click  the  “Review  Data”  link.  2. Double  click  on  the  WE@RIT  folder.  3. Double  click  on  the  file  you  want  to  review.  

QUESTIONS  TO  CONSIDER  BASED  ON  YOUR  OBSERVATIONS:  

• Were  you  able  to  observe  muscle  fiber  activation  by  performing  simple  weight  lifting  exercises  while  recording  muscle  action  potentials  from  electrodes  placed  over  muscles  of  interest?    

• Were  you  able  to  observe  the  coordination  of  muscle  fiber  activation  originating  from  the  biceps  and  triceps  when  performing  each  activity?  

• Were  there  observable  differences  in  muscle  fiber  activation  as  indicated  by  the  EMG  levels  when  manipulating  different  weights