ILLINOIS STATE UNIVERSITY
School of Kinesiology and Recreation
KNR 482
EMG: MUSCLE ACTIVITY PHASES DURING BASIC MOVEMENTS
OBJECTIVES:
1. To introduce electromyography (EMG) as a method of qualitatively evaluating muscle function.
2. To gain experience with use of the optotrak kinematic analysis system.
3. To qualitatively evaluate phases of eccentric, concentric, and isometric muscle activity during
simple elbow movements.
References:
From the 482 website, review the articles related to EMG.
INTRODUCTION
Electromyography (EMG) is an evaluative technique used to monitor electrical impulses in muscle
tissue during muscle activation. Muscle activation can produce movement against an outside
resistance such as gravity (concentric activity or shortening under tension), slow down movement
produced by an outside force (eccentric activity or lengthening under tension) or prevent movement
(isometric activity or tension development with no change in length).
The function of a muscle during joint movement is not always evident based on anatomic location
alone. Understanding muscle function is complicated by the number of muscles with similar
attachments on the skeleton, the changes in joint and muscle mechanics as the segments rotate,
and the intricate innervation patterns of the muscles. EMG provides an accurate indication of
muscle activation and the pattern of activation during a movement.
Muscle fibers are the structural unit of muscle activation, and are organized into functional
units known as motor units. A motor unit consists of a number of muscle fibers commonly innervated
by a single motor neuron. The neuromuscular system modifies the total tension output of a skeletal
muscle by 1) varying the number of motor units active (motor unit recruitment); 2) varying the
frequency of firing of the participating motor units (rate coding) and 3) selecting different types
of motor units to be involved in the activation. Synchronization of motor units is a combination of
the above, and characterizes coordinated or mature motor behavior.
When an action potential is transmitted from the CNS to a peripheral muscle, all fibers in the
motor unit develop tension. EMG records the electrical signal present in a muscle and indicates: (1)
the sequence of muscle activation; (2) the duration of muscle activation; (3) qualifies the magnitude
of muscle activation (increased EMG activity may reflect increased tension in the muscle), and (4)
the type of muscle activation (eccentric, concentric or isometric), if and only if the direction of
joint movement is known.
Electrical Mechanical Delay (EMD) is the brief period of time that elapses between the
stimulation of a muscle and the initiation of tension. During this time, the depolarization causes
release of Calcium into the sarcoplasm, the myosin cross-bridges attach to the active sites on the
actin to develop tension, and muscle laxity is removed allowing for force to be transmitted to the
bony attachments. The length of EMD may vary between subjects and different muscles within the
same subject. Shorter EMD times are associated with higher percentages of fast twitch fibers in
the muscle and a highly trained state.
You will work in groups for this project. Example EMG and elbow kinematic data will be collected for
one (or more) subject. Surface electrodes will be applied over the belly of the Biceps Brachii and
the Triceps Brachii muscles. The electrodes are connected to the computer through an A/D board.
The optoelectronic system will be used to determine the flexion and extension phases of the
activity. While reviewing the EMG relative to the joint position, note the amplitude and timing
(frequency) of muscle activity during specified movements with and without additional resistance
In random order, each subject will perform the following activities (note the condition identifiers
associated with each):
A. Slow Movement Speed
1) Sagittal Plane - Elbow flexion/extension (Condition 1 [C1])
2) Sagittal Plane - Elbow flexion/extension-10 kg. (C2)
3) Horizontal Plane - Elbow flexion/extension. (C3)
B. Fast Movement Speed
4) Sagittal Plane - Elbow flexion/extension. (C4)
5) Sagittal Plane - Elbow flexion/extension-10 kg. (C5)
6) Horizontal Plane - Elbow flexion/extension. (C6)
C. No Movement
7) Sagittal Plane - 90 degree elbow flexion-10 kg. (C7)
Using the two-sided sensor tape, attach the EMG sensors to the RIGHT side of the subject
over
a) the belly of the biceps brachii
b) the belly of the triceps brachii
Attach the ground sensor to the right side of the subject over the ulnar tuberosity (make sure you
attach the correct end over the reference)
Wrap around the sensors using the athletic wrap---ensure the wires are not free to snag on
anything.
Connect the lead from the Biceps into Channel 1 (CH 1), the lead from the Triceps into CH2, and the
lead from the ground into Ref on the small connector box. Attach one end of the cable to the small
connector box, and the other end to “A” on the transmitter pack.
CAREFULLY, place the transmitter pack and the small connector box into the pockets of the case,
and put the case onto the subject (hang it on the left side of the subject).
Attach the reflective markers to the RIGHT side of the subject over
a) the acromion process
b) the lateral epicondyle
c) the radial stylus
Note: ensure that the subject’s clothing will not obscure the markers, and that the strap
from the case will not interfere with the marker on the acromion process.
Disconnect the BNC cables for Fx and Fy from the breakout box. Note which connectors they
were attached to. (you will need to reattach them after data collection; this is a critical
step).
Connect the BNC cables for the Biceps and Triceps to connectors 1 and 2, respectively, on
the breakout box.
Use the following protocol to verify and calibrate the optotrak and EMG data:
1)
Activate the Vicon Motus program
2)
Select Cancel
3)
Select New Trial (icon or File tab)
4)
Select “Use a Template”
5)
Select “482 EMG Lab”
6)
Click Import; timer will appear, when it is gone click Close.
7)
Minimize the Vicon Motus program.
8)
Activate the Myomonitor Analog Output program
9)
Click start; verify that it is receiving data.
10) Restore the Vicon Motus program
11) Select “Capture” (note it will prompt you to save the trial; use the default trial name and
save it to the directory 48208). For reference purposes, you should write down the default
name used by Motus and the condition name you will use when you save the trial to the T
drive.
a. Note the sampling rate for the optotrak (Camera frequency)
b. Note the sampling rate for the EMG (Analog control, frequency)
c. Note the duration of the sample (this is the same for both EMG and video
12)
Test that you are getting signals from the biceps and the triceps.
a. Click on the View Analog icon, and wait for the oscilloscope screen to appear.
b. Have the subject perform resisted flexion and extension, and note the EMG tracing.
If the EMG is not correct, try reattaching the sensor over the offending muscle,
and repeat the test.
c. Close the collection window and return to the main menu.
13) You will need to calibrate the camera.
a. Set the calibration triangle over the force platform. As you stand facing north, the
3 reflective balls should be on the south side of the FP, and the single reflective
ball along the west side of the force platform.
b. Select the 24 cm calibration wand.
c. Select “Capture Calibration” from the menu. Note that the calibration is 30 s in
duration.
d. Press the “Clear Video” icon, and answer yes to the prompt.
e. Use the 24 cm reflective wand.
f. Press the red record button
g. For the 30 second calibration period, wave the 24 cm wand thoroughly over the
volume to be calibrated (ie in the general area of the right arm over the force
platform).
h. Check the “standard error for wand length” ; the wand length should be close to .24
m. If not, recapture the calibration.
You are now ready to collect a trial
14) Sit the subject over the force platform, with the right side to the cameras.
15) Randomly select one of the conditions to perform, and position the arm accordingly.
16) Select “Capture Data” . Wait until the three cameras flash and become brightly lit.
17) In the top right corner, set the duration to 10 s.
18) Press the record button.
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Close the data capture window (click on X in top right corner)
Select “identify paths”. A new window will open up.
Verify that the markers are tracked correctly, with no crossing over of the markers.
Close the identify paths window
Click ok (acknowledge that not all points may be followed; this message may not show up,
depending on how cleanly the markers were tracked)
Select “Process All” to calculate the angles and the process the EMG data
Press Save again (this will save all of the processed data)
Select Export data (use either File menu or the icon)
Select Export Data Set Below
Select the 3D angles, EMG data, and filtered EMG data sets (note: press the Ctrl key while
clicking on the three file types).
Click OK
Identify the directory for storing YOUR data (remember your ID number). The directory
will be T:\482\procEMG\Sx, where x is your ID number).
Highlight all of the data sets to be exported
Select Edit Prefix
Change file name (prefix) to format SxCyTz, where x is your subject ID typed once
Click OK
Collect another condition, by repeating the directions from 11 to 27, or simply select
Capture and press the Clear Data Icon.
WHEN DATA COLLECTION IS COMPLETE, DISCONNECT THE CABLES FOR THE BICEPS
AND THE TRICPS FROM THE CONNECTOR BOX, AND RECONNECT THE CABLES FOR F X
AND FY. If you fail to do this, it could waste a lot of time for people collecting thesis data.
Use the following protocol to analyze the data (Note: you need to have a paper and a pen
handy to record the results).
This will follow soon.
Problems:
Your manuscript (written in the format of the journal you used for the balance project) should
include an introduction, methods, results, discussion and reference section. Be sure to address the
following as appropriate:
1) What is EMG?
2) Describe and explain the differences in biceps and in triceps activity between:
a) slow sagittal unweighted" movement and "slow sagittal weighted" movement (10kg)
b) "slow sagittal unweighted" movement and "fast sagittal unweighted" movement
c) "slow horizontal unweighted" movement and "fast horizontal unweighted" movement
3) Why are both the biceps and triceps active during the "No-Movement" figure?
4) Calculate the range of motion (ROM) for the "slow, sagittal, unweighted" movement.
a) what is the beginning angle?
b) what is the terminal (ending) flexion angle?
c) Show how you calculate the total range of motion:
5) Explain (in your methods) the steps required to determine if muscle action is eccentric,
concentric, or isometric.
6) Provide an explanation for the delay between muscle activation and joint movement? On which
figures is pre-activation of the muscle evident?
i.
Explain why the range values differ. Account for the
AnteroPosterior and Mediolateral directions of the base of support.
b. Consider the Xspeed and Yspeed values:
i.
Explain why the speed values differ.
ii.
How does the difference in speed compare to the difference in
range?
c. What features of the stabilogram account for your answer to part c ii?