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“The Use of EMG to Determine the Electrical Activity Differences between Concentric and
Eccentric Contractions Along With the Correlation of Other Factors”
ABSTRACT: This investigation addressed the differences
between the electrical activities of a concentric
(shortening) muscle contraction versus an eccentric
(lengthening) muscle contraction through
electromyography (EMG) in the human biceps,
brachioradialis, and deltoid muscles. I also sought to
determine if muscle strength, subcutaneous fat or mass
of the subject had any bearing on the results. The
hypothesis of the research states that the concentric
muscle contractions will show higher electrical activity on
the EMG than the eccentric contractions. With this
finding, fitness trainers and rehabilitation experts may
want to revamp exercise programs to focus more
extensively on the eccentric contraction. The original
hypothesis proved to be correct. With twenty-nine
human subjects, in every instance, the concentric
contraction generated more electrical activity than the
eccentric contraction. However, other factors such as the
maximum strength, subcutaneous fat of the bicep, and
body mass assumed no correlations with the EMG data
gathered. In conclusion, the research was successful in
proving the electrical activity differences; however,
various other correlations were found unsuccessful
throughout the data accumulated in the investigation.
INTRODUCTION: This investigation focuses on important
physiological concepts. Neuromuscular transmission, the
firing of action potentials in the muscle, and cross bridge
cycling are the basic foundations behind
electromyography (EMG). The research focuses on two
types of muscle contractions: the concentric contraction
and the eccentric contraction. General knowledge
reveals that performing a concentric contraction, such as
walking up stairs, is more difficult than performing the
eccentric contraction, walking down the stairs. This
allowed for my hypothesis to develop. I believe the
concentric contraction should show more electrical
activity in the EMG than the eccentric contraction.
With the use of 29 human subjects, the research focused
on three muscles: the biceps, the brachioradialis, and the
deltoid. With a seven pound dumbbell, a bicep curl using
both the concentric and eccentric motions was used to
measure electrical activity of the biceps and
brachioradialis, while a lateral shoulder raise was used for
the deltoid.
By: Autumn Minor with Dr. B. Hamilton
Waynesburg University Department of Biology
INTRODUCTION CONTINUED: The EMG measured both area
and amplitude, area being the sum of the mechanical activity of
the muscle during the contraction and amplitude being the
maximum electrical activity. The measurement of the electrical
activity provided means for the main area of investigation of the
research; however, the investigation also correlated EMG
amplitude with maximum strength (by performing maximum
effort curl and raise preliminaries in each subject), with
subcutaneous fat measurements of the bicep, and the subject’s
body mass to determine any differences in EMG readings.
The research was done to help aid in the fitness realm. If the
concentric contraction did prove to have higher electrical
activities than the eccentric contraction, personal trainers and
rehabilitation experts may want to focus more on the eccentric
motion to help in training and rehab.
AIMS:
To investigate whether the concentric contraction revealed
more electrical activity than the eccentric contraction.
To use the above information to aid the fitness realm in the
development of training and rehabilitation techniques involving
a more eccentric contraction centered work-out.
To correlate strength of the subject with his/her EMG
amplitude.
To correlate subcutaneous fat of the subject with EMG
amplitude.
To correlate subject’s body mass with EMG amplitude.
RESULTS CONTINUED: GRAPH 3
RESULTS
0.16
GRAPH 1:
0.14
3 Muslces-Concentric Vs Eccentric Contraction: EMG AREA
0.045
E
M
G
C
o
n
c
e
n
t
r
i
c
0.04
0.035
0.03
0.12
A
m 0.1
p
l
i 0.08
t
u
d 0.06
e
deltoid
biceps
brachioradialis
Linear (deltoid)
Linear (biceps)
Linear (brachioradialis)
0.04
0.02
Biceps Concentric Contraction AREA
Biceps Eccentric Contraction AREA
0.025
0
0
20
40
Brachioradialis Concentric Contraction AREA
60
80
100
120
Maximum Effort
Brachioradialis Eccentric Contraction AREA
0.02
Deltoid Concentric Contraction AREA
Deltoid Eccentric Contraction AREA
0.015
0.01
Graph 3 represents the correlations between EMG
amplitude and maximum effort for all three muscle groups.
The graph reveals relatively straight trendlines, which proves
there is no correlation between strength and EMG readings.
0.005
GRAPH 4:
0
Sub Cutaneous Fat Measurement Vs Biceps Concentric
Contraction Amplitude
Concentric/Eccentric Contractions AREA
Graph 1 shows the values for EMG area of the three muscle
groups. On the far left is the biceps muscle concentric
contraction, followed by the eccentric contraction. Next is the
brachioradialis and finally the deltoid. The y-error bars represent
the standard error of the mean.
0.05
0.045
0.04
E
M 0.035
G
0.03
A
m
p 0.025
l
i
0.02
t
u
d 0.015
e
0.01
biceps
Linear (biceps)
0.005
GRAPH 2:
0
0
5
10
15
20
25
Skin Fold Values of the Bicep
3-Muscles-Concentric vs Eccentric Contraction: EMG AMPLITUDE
0.08
METHODS:
I received participation from 29 subjects (WU students) and
asked for each subject to complete a simple survey involving age,
weight, and activity level participation.
Each subject performed a maximum effort bicep curl and
lateral shoulder raise in the fitness center.
Each subject was taken to the lab where first, the bicep muscle
was hooked to three electrodes (one being the ground
electrode).
The BIOPAC EMG software was used to measure the subject’s
electrical activity during the concentric and eccentric contraction
of a bicep curl using a seven pound dumbbell.
The process was repeated with the brachioradialis.
The process was again repeated with the deltoid and with a
lateral shoulder raise rather than a bicep curl.
The subcutaneous fat of the subject’s bicep was measured
with a skin fold caliper.
Results were confidentially compiled and analyzed.
EMG Concentric Contraction Amplitude Vs. Maximum
Effort
CONCLUSIONS:
The average concentric contraction produced more electrical
activity than the eccentric contraction in each of the three
muscles studied (biceps, brachioradialis, and deltoid) in both
the EMG area and the EMG amplitude.
There appears to be no correlation between the EMG
readings of amplitude (maximal electrical activity) and strength
(maximum effort) in any of the three muscles.
There also appears to be no correlation between
subcutaneous fat on the bicep and EMG amplitude in any of
three muscles investigated. Only the graph of the biceps is
shown; however, the two other muscle groups revealed similar
results.
There is no correlation between the EMG readings of
amplitude and body mass (weight) of the subject in any of the
three muscles studied.
0.07
0.06
Biceps Concentric Contraction AMPLITUDE
Graph 4 reveals the relationship between subcutaneous fat
measurement of the bicep and EMG concentric amplitude in the
bicep. The graph shows a straight trendline, which reveals no
correlation.
ACKNOWLEDGMENTS: I would like to take the time to give a
special thanks to Waynesburg University department of
biology for giving me the funds and supplies needed to
perform my research. I would like to thank Dr. Brian Hamilton,
professor of physiology, for all his help in planning and
performing the research. I also would like to thank all of my
subjects who willingly participated in the research. Without
each of you, this project would not have been a success.
GRAPH 5:
Weight Vs Bicep Concentric Contraction Amplitude
0.05
Biceps Eccentric Contraction AMPLITUDE
0.05
0.045
0.04
Brachioradialis Concentric Contraction AMPLITUDE
0.04
E
M 0.035
G
Brachioradialis Eccentric Contraction AMPLITUDE
0.03
Deltoid Concentric Contraction AMPLITUDE
0.02
Deltoid Eccentric Contraction AMPLITUDE
0.03
A
m
p 0.025
l
i
0.02
t
u
d 0.015
e
0.01
0.01
0.005
0
0
0
Concentric & Eccentric Contraction AMPLITUDE
Graph 2 is set up in accordance with Graph 1. Graph 2 represents
EMG Amplitude.
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100
150
200
250
300
THE FITNESS REALM: The major thesis of the research stated
that the concentric contraction created more electrical activity,
both area and amplitude, than the eccentric contraction.
Personal trainers and rehabilitation professionals may want to
study this when working on strengthening individuals. People
may want to focus more on a workout centered around
eccentric contractions. This could allow injured individuals to
become stronger over a shorter time period along with
experiencing less pain. I would be interested to see further
research focused on training individuals over a period of time
using both methods. This type of research would be an
interesting investigation.
350
Weight (lbs)
Graph 5 represents the relationship between body mass
in pounds versus EMG amplitude in the biceps. The graph
shows a straight trendline and reveals no correlation.