EMG Lab Data Collection
Toru Tanaka, Miguel Narvaez, Adam Bruenger, and
members of the Spring Semester KIN 831 Course
• Worn about subject’s waist
• Receives incoming voltage signals (e.g.,
EMG, force transducers, metronome,
electrogoniometer)
• 2 sets of 8 pairs of differential leads
•1 common (ground) lead per set
•1 set of 8 DC differential channels
• Amplifies incoming analog signals
• 2 sets of pairs of 8 differential
channels (gain set at 1, 2, 5, or 10 K)
•8 DC differential channels (gain set
at 1, 1.333, 2, or 4 K)
• Samples
• Each of 16 differential channels at 8
KHz
• Each of 8 DC differential channels
at 1.6 KHz
• Converts analog signals into digital
signals
• Transmits digital signal to receiver via
fiber optic cable
MYOPAC Belt Unit
• Receives digital
optical signals from
MYOPAC belt unit
• Converts digital
signals back to analog
signals
• Makes signals
available to suitable
analog signal
recording system (e.g.,
analog to digital
converter,
oscilloscope,
computer)
•Full scale output of
receiver unit = 5 volts
MYOPAC Receiver Unit
Output of signal to
computer
Analog to digital
converters of input signals
Calibration of Input Signals
• EMG – signals amplified by selected gain
(assume linear amplification of all signals)
• Metronome – only temporal signal needed; not
concerned for magnitude of signal
• Electrogoniometer – check voltage output over
range of angles expected; assume linearity of
output signal
• Torque – check torque value at expected
maximum and minimum; assume linearity of
output signal (see next slide)
• Measure length of calibration bar
from pivot to center of cross
member (e.g., 0.765 m)
•Level calibration bar
•Load calibration bar with known
mass (e.g., 40 kg  392.4 N)
•Torque = force x perpendicular
distance (e.g., 392.4 N x 0.765 m
= 300.186 Nm)
•Use volt meter to read output
voltage for known torque (e.g.,
5.31 volts)
•Reorient calibration bar in vertical
position
•Output torque should = 0 volts
(actual voltage = 0.01volts)
•Calculate volts per unit of torque
assuming linearity of output signal
(e.g., 56.64 Nm per volt)
Calibration of Torque Signal
Identify Central
Contractile Region
of Muscles to be
Tested
• Use anatomical reference
source
• Apply resistance to prime
movement of muscle while
subject contracts muscle
• Palpate muscle (e.g., rectus
femoris)
• Attempt to distinguish from other
muscles in vicinity (e.g., vastus
lateralis and vastus medialis) to
reduce chance of cross talk
Prepare Skin for Surface Electrodes
1. Clean skin
2. Shave skin
3. Clean skin
4. Abrade skin
5. Clean skin
Position Surface
Electrodes
• Use pair of electrodes for
common mode rejection
• Determine position near
belly of muscle to be
recorded
• Orient pair of electrodes
with respect to line of pull of
muscle and/or orientation of
muscle fibers
• For consistency, measure
distance between recording
surfaces
Prepare Additional
Muscles for Surface
Electrodes
Medial head of
gastrocnemius
Note the use of
loop in electrode
wires prior to taping
leads and
electrodes. This
may protect
electrode from
dislodging if leads
are pulled.
Prepare Additional Muscles for Surface Electrodes
Long head of
biceps femoris
Familiarize
Subject with Test
Environment
Click
here
Restrict Extraneous
Movements
Experiment 1
Variation of Force of Isometric
Knee Extension
• Isokinetic dynamometer set
at 0 degrees/second
• Knee angle set at 45
degrees
• 3 different isometric
contractions: mild,
intermediate, and forceful
(subject attempts to maintain
constant force throughout
each contraction)
• Record rectus femoris EMG,
knee extension torque, and
joint angle
• All signal sampled at 2 KHz
• 3 data files
Based on your knowledge of
muscle mechanics and
electrophysiology what would
you expect?
Experiment 2
Electromechanical Delay
(EMD) in Isometric Knee
Flexion
• Isokinetic dynamometer set
at 0 degrees/second
Knee angle set at 45 degrees
• Record long head of biceps
femoris EMG
• Signal sampled at 2 KHz
• Subject begins with biceps
femoris relaxed, turns muscle
on quickly (quick contraction),
holds contraction for
approximately 3 seconds,
then relaxes muscle quickly
•Begin recording prior to
contraction and end recording
after turnoff of contraction
• 1 data file
Based on your knowledge of
muscle mechanics and
electrophysiology what would
you expect?
Experiment 3
Concentric Isokinetic Knee
Extension Under Different Loads
and Angular Velocities
• 3 angular velocities: 30, 90,
and 120 degrees/second
• 3 different isokinetic
contractions: mild, intermediate,
and forceful (subject attempts to
maintain constant torque
throughout each contraction)
• Record rectus femoris EMG,
knee extension torque, and joint
angle
• All signals sampled at 2 KHz
• 9 data files
Video Clip from Experiment 3
Mild 30 deg/sec
Mild 90 deg/sec
Intermediate 30 deg/sec
Intermediate 90 deg/sec
Intermediate 120 deg/sec
Forceful 30 deg/sec
Forceful 90 deg/sec
Forceful 120 deg/sec
Mild 120 deg/sec
Based on your knowledge of
muscle mechanics and
electrophysiology what would
you expect?
Eccentric Isokinetic Knee
Extension Under Different
Loads and Angular Velocities
• 3 angular velocities: 30, 90,
and 120 degrees/second
• 3 different isokinetic
contractions: mild,
intermediate, and forceful
(subject attempts to maintain
constant torque throughout
each contraction)
• Record rectus femoris
EMG and joint angle
• All signal sampled at 2 KHz
• 9 data files
*Note that recorded torque is the
difference between applied torque by
experimenter and resistive torque
applied by subject (unknown value)
Experiment 4
Video Clip from Experiment 4
30 degrees/sec mild, intermediate, forceful
90 degrees/sec mild, intermediate, forceful
120 degrees/sec mild, intermediate, forceful
Based on your knowledge of
muscle mechanics and
electrophysiology what would
you expect?
Experiment 5
Concentric Versus Eccentric
Contraction Under Similar and
Different Loads and Angular
Velocities
*Note that data for this
experiment was collected in
Experiment 3 and Experiment 4
Based on your knowledge of
muscle mechanics and
electrophysiology what would
you expect?
Skilled Movement Pattern Under
Similar and Different Loads and
Velocities
• Subject performs “skilled” movement
pattern consisting of standing from a
seated position, holding position,
going up onto the toes, holding
position, coming down from toes,
holding position, sitting back down on
the chair, and holding position
• Skilled movement pattern is
performed under 3 load conditions
(body only, body and bar (20 kg), and
body and 60 kg
• Subject performs skilled movement
pattern under 3 frequencies (slow,
intermediate, and fast) established by
beat of metronome
EMG from rectus femoris, long head
of biceps femoris, and medial head of
gastrocnemius and metronome
recorded at 2 KHz
• 9 data files
Experiment 6
A variation of Experiment 6 involves
recording several repetitions of the skilled
movement pattern to determine if there
are changes with experience and learning
Video Clip from Experiment 6
“Skilled” Movement Pattern
Body Weight
20 Kg Bar
60 Kg Load
Slow speed
Slow speed
Slow speed
Intermediate speed
Intermediate speed
Intermediate speed
Fast speed
Fast speed
Fast speed
Based on your knowledge of
muscle mechanics and
electrophysiology what would
you expect?
Experiment 7
Fatigue Under Maximum
Isometric Knee Extension
• Subject attempts to hold
maximum isometric knee
extension until extensors greatly
fatigued
• EMG signal of rectus femoris
recorded at 2 KHz during early,
middle, and late phases of
fatigue of muscle
• Torque recorded to determine
consistency and drop-off
• Files of early, middle, and late
phases of fatigue recorded
Video Clip from Experiment 7
Muscular Fatigue
Start to middle of contractile period
Near end of contractile period
Fatigued
Based on your knowledge of
muscle mechanics and
electrophysiology what would
you expect?