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Surface Electromyographic Analysis of Exercises for the Trapezius and Serratus Anterior Muscles

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This study used a prospective, single-group repeated-measures design to analyze differences between the electromyographic (EMG) amplitudes produced by exercises for the trapezius and serratus anterior muscles. To identify high-intensity exercises that elicit the greatest level of EMG activity in the trapezius and serratus anterior muscles. The trapezius and serratus anterior muscles are considered to be the only upward rotators of the scapula and are important for normal shoulder function. Electromyographic studies have been performed for these muscles during active and low-intensity exercises, but they have not been analyzed during high intensity exercises. Surface electrodes recorded EMG activity of the upper, middle, and lower trapezius and serratus anterior muscles during 10 exercises in 30 healthy subjects. The unilateral shoulder shrug exercise was found to produce the greatest EMG activity in the upper trapezius. For the middle trapezius, the greatest EMG amplitudes were generated with 2 exercises: shoulder horizontal extension with external rotation and the overhead arm raise in line with the lower trapezius muscle in the prone position. The arm raise overhead exercise in the prone position produced the maximum EMG activity in the lower trapezius. The serratus anterior was activated maximally with exercises requiring a great amount of upward rotation of the scapula. The exercises were shoulder abduction in the plane of the scapula above 120 degrees and a diagonal exercise with a combination of shoulder flexion, horizontal flexion, and external rotation. This study identified exercises that maximally activate the trapezius and serratus anterior muscles. This information may be helpful for clinicians in developing exercise programs for these muscles.
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Surface Electromyographic Analysis of
Exercises for the Trapezius and Serratus
Anterior Muscles
Richard A. Ekstrom, PT, DSc, MS, OCS
1
Robert A. Donatelli, PT, PhD, OCS
2
Gary L. Soderberg, PT, PhD, FAPTA
3
Study Design: This study used a prospective, single-group repeated-measures design to analyze
differences between the electromyographic (EMG) amplitudes produced by exercises for the
trapezius and serratus anterior muscles.
Objective: To identify high-intensity exercises that elicit the greatest level of EMG activity in the
trapezius and serratus anterior muscles.
Background: The trapezius and serratus anterior muscles are considered to be the only upward
rotators of the scapula and are important for normal shoulder function. Electromyographic studies
have been performed for these muscles during active and low-intensity exercises, but they have
not been analyzed during high intensity exercises.
Methods and Measures: Surface electrodes recorded EMG activity of the upper, middle, and lower
trapezius and serratus anterior muscles during 10 exercises in 30 healthy subjects.
Results: The unilateral shoulder shrug exercise was found to produce the greatest EMG activity in
the upper trapezius. For the middle trapezius, the greatest EMG amplitudes were generated with 2
exercises: shoulder horizontal extension with external rotation and the overhead arm raise in line
with the lower trapezius muscle in the prone position. The arm raise overhead exercise in the
prone position produced the maximum EMG activity in the lower trapezius. The serratus anterior
was activated maximally with exercises requiring a great amount of upward rotation of the
scapula. The exercises were shoulder abduction in the plane of the scapula above 120° and a
diagonal exercise with a combination of shoulder flexion, horizontal flexion, and external rotation.
Conclusion: This study identified exercises that maximally activate the trapezius and serratus
anterior muscles. This information may be helpful for clinicians in developing exercise programs
for these muscles. J Orthop Sports Phys Ther 2003;33:247–258.
Key Words: scapula, shoulder, strength, upper extremity
The upper trapezius, lower trapezius, and serratus anterior
muscles are considered to be the only upward rotators of
the scapula.
39
Therefore, these muscles play an integral part
in scapular movement during scapulohumeral rhythm, a
motion that has been analyzed by many authors.
2,13,15,20,41
In these studies, the total amount of scapular upward rotation was found
1
Assistant Professor, Department of Physical Therapy, University of South Dakota, Vermillion, SD.
2
National Director of Sports Rehabilitation, Physiotherapy Associates, Alpharetta, GA.
3
Professor, Department of Physical Therapy, Southwest Missouri State University, Springfield, MO.
This work was performed by the primary author for partial fulfillment of a DSc degree from Rocky
Mountain University of Health Professions, Provo, Utah. Study approved by the Institutional Review
Board of the University of South Dakota and Rocky Mountain University of Health Professions.
Send correspondence to Richard A Ekstrom, Assistant Professor, Physical Therapy Department, University
of South Dakota, 414 East Clark St., Vermillion, SD 57069. E-mail: rekstrom@usd.edu
to range from 58° to 65° and
glenohumeral motion ranged from
103° to 112.5° during full shoulder
elevation. There seems to be a
consensus as to the general pat-
tern of movement. During the first
30° to 60° of humeral flexion or
abduction, the scapula tends to
find a position of stability with
variable movement between indi-
viduals.
20
There is very little up-
ward rotation of the scapula
during this period. During mid-
range of shoulder elevation (from
about 80° to 140°) a substantial
amount of scapular upward rota-
tion occurs, and then above 140°
the amount of rotation decreases.
2
Scapulohumeral rhythm or
scapular position may be altered
with different conditions that in-
clude increased loading, muscle
fatigue, impingement syndrome,
instability of the glenohumeral
joint, or postural changes.
1,23,25,30–
32,34–36
Ludewig and Cook
30
re-
ported that patients with shoulder
impingement had increased EMG
activity in the trapezius, but had
decreased EMG activity in the ser-
ratus anterior muscle during
shoulder elevation in the scapular
plane. It is not known whether
weakness or changes in motor re-
cruitment of the serratus anterior
and trapezius muscles is the cause
or the result of impingement. One
goal of shoulder rehabilitation
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should be to restore normal scapulohumeral rhythm
and that may require exercises focusing on the
trapezius and serratus anterior muscles.
Electromyographic analysis of the trapezius and
serratus anterior muscles has been performed during
active humeral elevation and during rehabilitation-
type exercises.
3,4,8,9,11,1315,18,20,28,3033,35,36,38,43
Gener-
ally, the studies report increasing EMG activity in the
trapezius and serratus anterior as the shoulder is
actively elevated to end range.
A variety of exercises have been recommended for
strengthening the serratus anterior and trapezius
muscles based on the level of EMG activity. Moseley
et al
38
performed an EMG study of the shoulder
muscles in 9 subjects during 16 different exercises,
each repeated 10 times at low intensity. They found
that rowing and the military press produced maxi-
mum EMG activity in the upper trapezius. For the
middle trapezius, they identified 4 exercises that they
considered optimal: horizontal extension with the
glenohumeral joint in neutral or external rotation,
shoulder extension, and rowing. Shoulder abduction,
rowing, and horizontal extension with the
glenohumeral joint in neutral or external rotation all
qualified as optimal exercises for the lower trapezius
based on the EMG levels. The exercises suggested for
strengthening the serratus anterior muscle were
shoulder flexion or abduction and shoulder abduc-
tion in the plane of the scapula.
Hintermeister et al
18
performed an EMG study of
the shoulder using elastic bands for resistance during
7 exercises performed at a relatively low load. They
recommended a shoulder shrug exercise for the
upper trapezius muscle, a seated rowing exercise for
the trapezius muscles, and a forward punch exercise
(scapular protraction) for the serratus anterior
muscle.
Serratus anterior muscle activity during selected
rehabilitation exercises was studied by Decker et al.
11
All the exercises were performed with the arm below
shoulder height with resistance provided by body
weight, elastic cords, or dumbbells. The intensity of
each exercise was not precisely controlled. A serratus
anterior punch exercise (scapular protraction), shoul-
der elevation in the plane of the scapula, push-ups
with maximum scapular protraction, and an exercise
called the dynamic hug (scapular protraction) consis-
tently elicited serratus anterior muscle EMG activity
greater than 20% of a reference contraction.
None of the EMG studies that have evaluated
exercises for the trapezius and serratus anterior
muscles were performed with well-controlled high-
intensity exercises. In addition, the muscle tests that
produced the maximum voluntary isometric contrac-
tion for normalization of the data were not identified
in some studies. If identified, it was often question-
able whether the tests were actually adequate to
produce maximum EMG activity of the muscle.
The purpose of this study was to identify which of
several exercises performed at a high level of inten-
sity elicited the greatest levels of EMG activity in the
trapezius and serratus anterior muscles.
METHODS
Subjects
Thirty volunteers (10 male and 20 female) whose
ages ranged from 22 to 46 years (mean = 27.2 years)
participated in the study. The subjects filled out a
short history form and were excluded from the study
if they had shoulder problems such as tendonitis,
adhesive capsulitis, instability, or impingement. Par-
ticipants signed consent forms approved by the Uni-
versity of South Dakota Institutional Review Board
and the Rocky Mountain University of Health Profes-
sions Institutional Review Board.
Instrumentation
Using a bipolar configuration, 2 silver/silver chlo-
ride disposable surface recording electrodes
(Medicotest A/S, O
/lstykke, Denmark), each with a
pickup diameter of 10 mm, were connected with
cables to an 8-channel Noraxon Myosystem 1200
EMG system (Noraxon USA, Inc., Scottsdale, AZ).
The Myosystem 1200 has a sensitivity of ±100 nV, a
differential input impedance of greater than 10 M,
a common mode rejection ratio (CMRR) of greater
than 100 dB at 60 Hz, and a frequency response of
10 to 500 Hz. The Myosystem 1200 was interfaced
with the computer via a 16-channel, 12-bit A/D card
(Computer Boards, Inc., Middleboro, MA). The sam-
pling rate was set at 1000 Hz per channel.
All data were stored on a Gateway Solo 9300LS
personal computer (Gateway Inc., Poway, CA) and
data were processed and analyzed using the
MyoResearch 2.02 software (Noraxon USA, Inc.,
Scottsdale, AZ).
Procedures
Electromyographic data were collected from the
muscles of the right shoulder of each subject. The
upper, middle, and lower trapezius, and serratus
anterior muscles were evaluated during the 10 differ-
ent exercises illustrated in Figures 1 to 10.
For electrode placement over the upper trapezius,
the shoulder was positioned in 90°of abduction. Two
electrodes were placed so that they ran parallel to the
muscle fibers and positioned so that 1 electrode was
superomedial and 1 inferolateral to a point 2 cm
lateral to one-half the distance between the C7
spinous process and the lateral tip of the
acromion.
17,26
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FIGURE 1. Unilateral shoulder shrug in the standing position.
FIGURE 2. Unilateral row in the prone position.
For the middle trapezius, the electrodes were
placed parallel to the muscle fibers between the spine
of the scapula and thoracic spine. One electrode was
placed medial and 1 lateral to a point 3 cm lateral to
the second thoracic spinous process.
10
For the lower
trapezius, the shoulder was positioned in 90°of
flexion and the electrodes were placed on an oblique
vertical angle with 1 electrode superior and 1 inferior
FIGURE 3. Arm raise above the head with the upper extremity in
line with the lower trapezius muscle fibers in the prone position.
FIGURE 4. Shoulder horizontal extension with external rotation in
the prone position.
to a point 5 cm inferomedial from the root of the
spine of the scapula.
10
For the serratus anterior, the
shoulder was abducted to 90°and the electrodes were
placed vertically along the midaxillary line at rib
levels 6 through 8.
6
A common reference electrode
was placed over the C7 spinous process.
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FIGURE 5. Shoulder external rotation with the shoulder abducted
90°and the elbow flexed 90°in the prone position with the elbow
supported on the table.
FIGURE 6. Shoulder abduction in the plane of the scapula above
120°in the standing position.
All sites for electrode placements were prepared by
abrading the skin with fine sandpaper and cleansing
the area with 70% isopropyl alcohol. Shaving of hair
was performed if necessary. The electrode pairs were
then applied with a center-to-center interelectrode
distance of 30 mm. The skin impedance was checked
FIGURE 7. Diagonal exercise with a combination of shoulder
flexion, horizontal flexion, and external rotation in the sitting
position.
FIGURE 8. Shoulder abduction in the plane of the scapula below
80°in the standing position.
with an ohm meter attached to the snap of each
electrode pair and was acceptable for the study if less
than 5000 .
10
For normalization of the EMG data, muscle-testing
positions as outlined for the trapezius and serratus
anterior muscles by Kendall et al,
24
as well as 5 other
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FIGURE 9. Bilateral scapular protraction with the shoulder horizon-
tally flexed to about 45°and the elbows flexed to about 45°in the
supine position.
muscle test positions were analyzed to determine
which test produced the maximum EMG activity for
each muscle. For the upper trapezius muscle, there
were 3 different muscle tests that produced maxi-
mum EMG activity in subjects. Two of the tests were
resisted shoulder shrug or shoulder abduction to 90°
with the head and neck rotated to the opposite side
and side-bent to the same side in both cases. A third
muscle test was performed with the shoulder flexed
to 125°. Two muscle tests were found to produce
maximum EMG activity in the middle and lower
trapezius. The muscle tests were performed in the
prone position with either the shoulder horizontally
extended and externally rotated, or with the arm
raised overhead in line with the lower trapezius
muscle fibers.
24
The maximum EMG amplitudes for
the serratus anterior were produced with a muscle
test either with the shoulder flexed to 125°or
abducted to 125°in the plane of the scapula. The
muscle test that produced the maximum EMG ampli-
tude in each muscle for each subject was then
considered the maximum voluntary isometric con-
traction (MVIC) for that muscle.
FIGURE 10. Unilateral shoulder press with full scapular protraction
with the shoulder flexed to 90°and the elbow fully extended in the
supine position.
Within each subject, the EMG values for each
muscle during each exercise were normalized as a
percentage of the highest EMG value produced by
that muscle during a MVIC. The EMG data for the
exercises were then expressed as percent maximum
voluntary isometric contraction (% MVIC).
For each exercise, the 5-repetition maximum (RM)
was determined for each subject prior to the testing
session. That intensity level which is in the range of
about 85% to 90% of maximum lifting capacity was
used during EMG data collection.
5
During EMG data
collection, each exercise was performed 3 times at a
slow movement rate of 5 seconds for each concentric
phase of the exercise. A metronome set at a rate of 1
beat per second was utilized to control the speed of
each repetition.
The exercise sequence for each subject was deter-
mined by simple random selection by drawing each
exercise from a box. Ten subjects performed the
exercises a second time on the same day after a
15-minute rest period to analyze test-retest reliability
of the EMG recordings.
The raw EMG data were full-wave rectified and
processed using a root-mean-square algorithm with a
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20-ms moving window. A 2-second time period from 1
of the 3 repetitions during each muscle test or
exercise, where the rectified, smoothed EMG ampli-
tude was the greatest, was quantified by the com-
puter. The data resulting from this time period were
utilized for analysis of each muscle test performed for
normalization and for each exercise.
Data Analysis
The SPSS Base 10.0 for Windows (SPSS Inc.,
Chicago, IL) computer program was used for data
analysis. An intraclass correlation coefficient (ICC
3,1
)
was used to determine the same-day test-retest reli-
ability of the EMG recordings.
42
A repeated-measures analysis of variance (ANOVA)
was applied when analyzing the data to determine if
there were significant differences in EMG activity for
specific muscles during the exercises. A separate
ANOVA was performed for each of the 4 muscles,
with the independent variable being exercise with 10
levels of comparison. A least significant difference
(LSD) pairwise multiple comparison analysis was
performed to determine the significance of the
differences among pairs of means. An alpha level of
0.05 was applied to all the data in determining
significant differences.
RESULTS
Reliability
The same-day test-retest ICCs for EMG recordings
from 10 subjects are documented in Tables 1 through
4 for each muscle during each exercise. The reliabil-
ity of the EMG recordings was generally excellent
(0.910.98) when the muscles worked as prime mov-
ers, except for the recordings for the upper trapezius
where the scores were less (0.810.89). Often, reliabil-
ity was less when the muscle worked as a synergist or
antagonist during the exercise rather than a prime
mover.
Electromyography Exercise Data
The EMG activity of each muscle during each
exercise, as well as the significant differences between
exercises, are displayed in Tables 1 through 4. Ex-
amples of the raw EMG recordings are displayed in
Figures 11 and 12.
DISCUSSION
The scapular upward rotator muscles are essential
for normal movement and function of the shoulder
girdle.
39
Therefore, it is important to be able to
effectively strengthen the trapezius and serratus ante-
rior muscles during rehabilitation of patients with
TABLE 1. Mean (±SD) EMG activation of the upper trapezius
expressed as a percentage of maximum voluntary isometric con-
traction (MVIC) for 10 shoulder exercises. Corresponding
intraclass correlation coefficients (ICC) for the EMG measure-
ments are also provided for each exercise.
Exercise % MVIC ICC
1. Unilateral shoulder shrug 119 ± 23* 0.81
2. Shoulder abduction in the plane of
the scapula above 120°79±19
0.80
3. Arm raise overhead in line with the
lower trapezius muscle fibers 79±18
0.89
4. Shoulder abduction in the plane of
the scapula below 80°72±19
0.75
5. Shoulder horizontal extension with
external rotation 66±18
0.83
6. Diagonal exercise with shoulder
flexion, horizontal flexion, and ex-
ternal rotation
66±10
0.81
7. Unilateral row 63 ± 17
0.91
8. Shoulder external rotation at 90°of
abduction 20±18
0.91
9. Unilateral shoulder press 7 ± 3 0.30
10. Bilateral scapular protraction 7 ± 5 0.94
* Significantly greater than exercises 2 through 10 (P0.05).
No significant difference between exercises 2 through 7, but
they all are significantly greater than exercises 8 through 10
(P0.05).
Significantly greater than exercises 9 and 10 (P0.05).
TABLE 2. Mean (±SD) EMG activation of the middle trapezius
expressed as a percentage of maximum voluntary isometric con-
traction (MVIC) for 10 shoulder exercises. Corresponding
intraclass correlation coefficients (ICC) for the EMG measure-
ments are also provided for each exercise.
Exercise % MVIC ICC
1. Arm raise overhead in line with the
lower trapezius muscle fibers 101 ± 32* 0.91
2. Shoulder horizontal extension with
external rotation 87±20
0.98
3. Unilateral row 79 ± 23
0.97
4. Unilateral shoulder shrug 53 ± 25
0.86
5. Shoulder abduction in the plane of
the scapula above 120°49±16
0.80
6. Shoulder abduction in the plane of
the scapula below 80°47±16
0.82
7. Shoulder external rotation at 90°of
abduction 45±36
0.87
8. Diagonal exercise with shoulder
flexion, horizontal flexion, and ex-
ternal rotation
21 ± 9 0.83
9. Unilateral shoulder press 12 ± 10 0.27
10. Bilateral scapular protraction 7 ± 3 0.86
* Significantly greater than exercises 4 through 10 (P0.05).
No significant difference between exercises 2 and 3, but both are
significantly greater than exercises 4 through 10 (P0.05).
No significant difference between exercises 4 through 7, but
they are all significantly greater than exercises 8 through 10
(P0.05).
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TABLE 3. Mean (±SD) EMG activation of the lower trapezius
expressed as a percentage of maximum voluntary isometric con-
traction (MVIC) for 10 shoulder exercises. Corresponding
intraclass correlation coefficients (ICC) for the EMG measure-
ments are also provided for each exercise.
Exercise % MVIC ICC
1. Arm raise overhead in line with the
lower trapezius muscle fibers 97 ± 16* 0.96
2. Shoulder external rotation at 90°of
abduction 79±21
0.96
3. Shoulder horizontal extension with
external rotation 74±21
0.92
4. Shoulder abduction in the plane of
the scapula above 120°61±19
§
0.98
5. Shoulder abduction in the plane of
the scapula below 80°50±21
§
0.94
6. Unilateral row 45 ± 17
§
0.80
7. Diagonal exercise with shoulder
flexion, horizontal flexion, and ex-
ternal rotation
39±15 0.94
8. Unilateral shoulder shrug 21 ± 10 0.05
9. Unilateral shoulder press 11 ± 5 0.20
10. Bilateral scapular protraction 5 ± 2 0.70
* Significantly greater than exercises 3 through 10 (P0.05).
Significantly greater than exercises 5 through 10 (P0.05).
Significantly greater than exercises 6 through 10 (P0.05).
§
No significant difference between exercises 4 through 6, but
they are all significantly greater than exercises 7 through 10
(P0.05).
TABLE 4. Mean (±SD) EMG activation of the serratus anterior
expressed as a percentage of maximum voluntary isometric con-
traction (MVIC) for 10 shoulder exercises. Corresponding
intraclass correlation coefficients (ICC) for the EMG measure-
ments are also provided for each exercise.
Exercise % MVIC ICC
1. Diagonal exercise with shoulder
flexion, horizontal flexion, and ex-
ternal rotation
100 ± 24* 0.94
2. Shoulder abduction in the plane of
the scapula above 120°96 ± 24* 0.96
3. Shoulder abduction in the plane of
the scapula below 80°62±18
0.93
4. Unilateral shoulder press 62 ± 19
0.98
5. Shoulder external rotation at 90°of
abduction 57±22
0.89
6 Bilateral scapular protraction 53 ± 28
0.80
7. Arm raise overhead in line with the
lower trapezius muscle fibers 43±17
0.68
8. Unilateral shoulder shrug 27 ± 17 0.85
9. Unilateral row 14 ± 6 0.97
10. Shoulder horizontal extension with
external rotation 9 ± 3 0.96
* No significant difference between exercises 1 and 2, but both are
significantly greater than exercises 3 through 10 (P0.05).
No significant difference between exercises 3 through 7, but
they are all significantly greater than exercises 8 through 10
(P0.05).
shoulder pathology. The EMG data presented may
assist physical therapists in developing exercise pro-
grams that will optimally activate the trapezius and
serratus anterior muscles.
Exercises for the Upper Trapezius
The shoulder shrug exercise produced the most
EMG activity in the upper trapezius (119% MVIC)
(Figure 1). Moseley et al
38
also performed a shrug
exercise, but it was not listed as one of their top 5
exercises for recruitment of the upper trapezius
muscle. They found that rowing (Figure 2) produced
the maximum EMG amplitude in the upper
trapezius, whereas in this present study, rowing pro-
duced an amplitude of only 63% MVIC. The rowing
exercise was performed in the same position in both
studies, so it is not clear why there is such a
discrepancy. Intramuscular fine-wire electrodes were
used in their study as compared to surface electrodes
in this study. The exercises were also performed at a
higher intensity in this present study. Hintermeister
et al
18
performed scapular exercises using an elastic
cord for resistance and also found that the shoulder
shrug produced maximum EMG activity in the upper
trapezius.
Exercises for the Middle Trapezius
For the middle trapezius, the prone arm raise
overhead (101% MVIC) and shoulder horizontal
extension with external rotation (87% MVIC) were
exercises that produced maximum EMG activity (Fig-
ures 3 and 4). These were performed in the same
positions that Kendall et al
24
recommend for muscle
testing of the middle and lower trapezius. Moseley et
al
38
found maximum EMG activity in the middle
trapezius during horizontal extension with neutral or
lateral rotation.
Exercises for the Lower Trapezius
The optimal exercise for activating the lower
trapezius was the arm raise overhead in line with the
lower trapezius muscle fibers and with the subject in
the prone position (97% MVIC) (Figure 3). This
exercise was performed in the same position as the
muscle test that produced a MVIC for normalization.
There are no other studies that have analyzed this
exercise with EMG.
Some patients may have shoulder pathology that
would make the above exercise contraindicated due
to the elevated position of the humerus. An alterna-
tive exercise that produced high levels of EMG
activity (79% MVIC) in the lower trapezius was prone
shoulder external rotation at 90°of abduction (Fig-
ure 5). Ballantyne et al
4
previously demonstrated that
external rotation of the shoulder at 90°of abduction
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FIGURE 11. Raw EMG recording of the activity in the serratus anterior muscle during shoulder abduction in the plane of the scapula above
120°. Three contractions with a total range of 02000 µV.
elicited considerable activity in the lower trapezius
muscle. This exercise causes maximum depression of
the scapula and isolates the lower trapezius from the
upper (20% MVIC) and middle trapezius (45%
MVIC) better than any other exercise.
A third exercise that produced relatively high EMG
activity (74% MVIC) in the lower trapezius was
shoulder horizontal extension with external rotation
(Figure 4). Moseley et al
38
reported EMG activity of
63% MVIC with this exercise. They identified shoul-
der abduction from 90°to 150°as the optimal
exercise for activating the lower trapezius (68%
MVIC). However, in this present study, it was found
that shoulder abduction in the plane of the scapula
above 120°(Figure 6) produced EMG activity of 61%
MVIC and was rated as the fourth best exercise.
Rowing exercises have been recommended for
strengthening the trapezius muscle.
18,38
Moseley et
al
38
recorded EMG activity of 112% MVIC for the
upper trapezius, 59% MVIC for the middle trapezius,
and 67% MVIC for the lower trapezius during row-
ing. Hintermeister et al
18
found that rowing activated
the trapezius muscles the best when the humerus was
first abducted to 90°. In this present study, the prone
rowing exercise created 79% MVIC in the middle
trapezius, 63% MVIC in the upper trapezius, and
45% MVIC in the lower trapezius. Therefore, it was
not found to be an optimal exercise for activating the
trapezius muscle as a whole. However, rowing may be
the exercise of choice for activating the trapezius in
early stages of rehabilitation if a patient should not
be performing shoulder elevation.
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FIGURE 12. Raw EMG recording of the activity in the upper trapezius muscle during the unilateral shoulder shrug exercise. Three
contractions with a total range of 05000 µV.
Exercises for the Serratus Anterior
Exercises that create upward rotation of the scapula
were found to produce much more EMG activity in
the serratus anterior than straight scapular protrac-
tion exercises. A diagonal exercise with a combina-
tion of shoulder flexion, horizontal flexion, and
external rotation (100% MVIC) and shoulder abduc-
tion in the plane of the scapula above 120°(96%
MVIC) generated the highest levels of EMG activity in
the serratus anterior (Figures 6 and 7). Moseley et
al
38
also found that shoulder elevation exercises from
120°to 150°produced maximum EMG activity in the
serratus anterior. The diagonal exercise reduces the
activity in the trapezius muscle, therefore, the ser-
ratus anterior muscle has to carry more of the load.
An advantage of this exercise for the serratus anterior
muscle is that patients with impingement problems
may be able to perform this exercise more easily than
a shoulder abduction exercise.
Exercise in the plane of the scapula was performed
below 80°and above 120°to avoid a range of motion
where shoulder impingement would most likely occur
(Figures 6 and 8). Exercise below 80°produced
significantly less EMG activity (62% MVIC) in the
serratus anterior when compared to exercise above
120°(96% MVIC). This is not surprising because the
majority of upward rotation of the scapula occurs in
ranges between 80°and 140°during shoulder abduc-
tion.
2
Many patients with impingement may be able
to exercise in the plane of the scapula above 120°as
long as the painful arc of movement is avoided.
Many authors recommend scapular protraction ex-
ercises for serratus anterior muscle strengthen-
J Orthop Sports Phys Ther Volume 33 Number 5 May 2003 255
RESEARCH REPORT
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ing.
11,18,22,40,44
In this present study, 2 protraction-
type exercises were evaluated. The first exercise was a
bilateral scapular protraction exercise (Figure 9)
fashioned after the dynamic hug exercise studied by
Decker et al.
11
This exercise produced EMG activity
in the serratus anterior that was 53% MVIC. The
second exercise was a supine unilateral shoulder
press exercise with full scapular protraction to end
range which produced 62% MVIC (Figure 10). This
activity level was consistent with what we found
during manual muscle testing using scapular protrac-
tion at 90°of shoulder flexion (57% MVIC).
Decker et al
11
performed scapular protraction-type
exercises using moderate resistance with an elastic
cord and found the activity in the serratus anterior to
be at the 31%-MVIC level for a serratus anterior
punch (protraction) exercise and a dynamic hug
exercise (protraction). Hintermeister et al
18
followed
a similar protocol to that of Decker et al
11
and also
used elastic cords for resistance. They found a for-
ward punch exercise to produce 49% MVIC in the
serratus anterior. It is not completely clear why these
exercises do not activate the serratus anterior to a
greater degree, however, it is evident that these
exercises do not produce adequate upward rotation
of the scapula, which seems to be a very important
factor for optimal activation of the muscle.
Simultaneous Activation of the Trapezius and Serratus
Anterior
Because the trapezius and serratus anterior muscles
work synergistically to produce upward rotation of
the scapula, the 2 exercises that best activated the 2
muscles simultaneously were identified. Performing
this type of exercise may be important in teaching
proper motor recruitment of the trapezius and ser-
ratus anterior muscles if the goal is to improve
scapular upward rotation and scapulohumeral
rhythm. The first exercise was the prone arm raise
overhead, which produced EMG activity in the 3 parts
of the trapezius that ranged from 79% to 101% MVIC
and activation levels in the serratus anterior that
could not be reliably measured (Figure 3). The
second exercise was shoulder abduction in the plane
of the scapula above 120°, which produced EMG
activity ranging from 49% to 79% MVIC in the 3
parts of the trapezius and 96% MVIC in the serratus
anterior (Figure 6).
Limitations
Research has demonstrated that as active tension
increases in a muscle, there is a linear or near-linear
increase in the EMG amplitude during isometric
contractions.
19,29,37,46
In this study, concentric con-
tractions were evaluated and it must be recognized
that there may have been changes in the EMG
recording due to changing muscle length and speed
of contraction.
12
This is always a concern when
performing EMG to evaluate exercises. However, it
has been demonstrated that there is a near-linear
relationship between force production and the EMG
recording with concentric or eccentric contractions if
the velocity of contraction is kept constant.
7,27
The
speed of contraction or muscle shortening in this
study was controlled as much as possible with the use
of a metronome during the exercises.
Most authors feel that surface EMG is appropriate
for superficial muscles.
6,10,12
The surface EMG signal
is a good representation of the activity of the whole
muscle. It also has been found that the reliability of
the surface EMG signal is better than analyzing
activity with intramuscular fine-wire electrodes.
17,21,27
However, cross-talk may be a limitation when using
surface electrodes during EMG recordings, especially
when analyzing small muscles.
16,45
We feel that cross-
talk was not a significant problem in this study
because we analyzed large superficial muscles.
Conclusions drawn about activation levels during
some exercises for the trapezius and serratus anterior
may not be valid because of unreliable EMG measure-
ments, especially when the muscles were acting as
synergists or antagonists. There were several exercises
in which the ICC scores for the EMG recordings for a
certain muscle dropped below 0.80 and, therefore,
the exercise must be interpreted with caution. How-
ever, this limitation does not affect the major findings
reported in this paper because the reliability was
generally good to excellent.
Because these results were obtained by studying
subjects without pathology of the shoulder girdle,
rather than patients with shoulder problems, caution
is warranted in extrapolating these findings to a
patient population.
CONCLUSION
The results would suggest that the upper trapezius
is best activated with the shoulder shrug exercise.
The middle trapezius demonstrated the greatest
amount of EMG activity with 2 exercises: shoulder
horizontal extension with external rotation and the
overhead arm raise exercise in the prone position.
For the lower trapezius, the overhead arm raise in the
prone position produced the most EMG activity.
Shoulder external rotation at 90°of humeral abduc-
tion is also an excellent exercise for activating the
lower trapezius. Shoulder abduction in the plane of
the scapula above 120°or a diagonal exercise with
shoulder flexion, horizontal flexion, and external
rotation that require a great amount of upward
rotation of the scapula produced the greatest activa-
tion of the serratus anterior. Shoulder abduction in
the plane of the scapula above 120°is also an
excellent exercise for coactivation of the trapezius
and serratus anterior. Scapular protraction exercises
256 J Orthop Sports Phys Ther Volume 33 Number 5 May 2003
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often used for exercising the serratus anterior pro-
duced EMG activity that was relatively low.
ACKNOWLEDGEMENTS
The authors thank Tuula Tyry, PhD, for her
assistance with EMG methods and data collection,
and Franklin Stein, OTR, PhD, for his assistance with
research methods and design.
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... The right shoulder of each participant was utilized for testing. studies [2,4,13]. Skin under the electrodes was shaved and cleaned with alcohol to reduce skin impedance (typically ≤ 10 kΩ). ...
... An intraclass correlation coefficient (ICC3,1) was used to detect same-day testretest reliability of the EMG data using the values of the three trials for analysis [4,24]. Test for normality (Kolmogorov-Smirnov) was found to meet the requirements for parametric statistics. ...
... The ICC scores obtained in this study are lower than in other EMG studies concerning shoulder muscle activation during rehabilitation exercises [4,24]. In contrast to those studies, which investigated isolated muscle movements, a full body exercise was performed in this study. ...
Thesis
Full-text available
The aim of the study was to quantify the activation of arm and shoulder muscles during a static therapeutic climbing exercise and to investigate the possibility of altering the muscle activation through arm position, hand support and wall inclination. Ten climbing experienced males without history of shoulder injury or pain performed a static climbing exercise in five different exercise positions (Jug, Undercling, Sidepull internal rotation (Sidepull_IR), Sidepull external rotation (Sidepull_ER) and Hip-roll) and five different inclination angles (0%, 5%, 10%, 15% and 20%) on a climbing wall. The Jug, Undercling, Sidepull_IR and Sidepull_ER exercise positions were performed double-handed as well as one- handed. An electromyographic (EMG) analysis (myon 320, surface electrodes) of these exercises of seven muscles (m. biceps brachii (BB), m. pectoralis major pars sternocostalis (PM.s), m. deltoideus pars spinalis (Delt.s), m. serratus anterior (SA), m. trapezius pars ascendens (Trap.a), m. trapezius pars transversa (Trap.t) und m. trapezius pars descendens (Trap.d)) of the right arm and shoulder was performed. The processed EMG Data were normalised using preliminary measured maximum voluntary isometric contraction (MVIC) values. Low to high muscle activation levels were shown during the different exercise variations (BB: 3 - 34 % MVIC, PM.s: 1 – 3 % MVIC, Delt.s: 14 – 65 % MVIC, SA: 2 – 12 % MVIC, Trap.a: 8 – 64 % MVIC, Trap.t: 20 – 58 % MVIC, Trap.d: 3 – 29 % MVIC). Significant main effects for the exercise position factor were found in all muscles, but with individual activation patterns for the different exercise positions. The exercise position Hip-roll revealed the greatest muscle activation in all muscles, except for the Trap.a. The release of one hand created a significant increase in activation in nearly every exercise position and muscle, with the exception of Delt.s. Except for PM.s and SA, all muscles showed a significant increase in activation at mainly 20% inclination angle. The static therapeutic climbing exercise seems to be an appropriate exercise in shoulder rehabilitation and exercise position, inclination and the release of one hand are appropriate possibilities of exercise intensity control.
... Decker et al. showed that the SA punch is one of the exercises that demonstrates the greatest activation of the SA, 94.4% MVIC, values similar to those obtained with the push-up plus standard and the dynamic hug exercise (Decker et al., 1999). Ekstrom et al. (2003) analysed muscle activity in the UT, medial trapezius, and SA during the performance of 10 exercises, including the unilateral shoulder press. This exercise is not considered an exercise for the early stages of rehabilitation and was performed at an intensity of 85% to 90% of one-repetition maximum. ...
... This exercise is not considered an exercise for the early stages of rehabilitation and was performed at an intensity of 85% to 90% of one-repetition maximum. Although a high load was used, it demonstrated activation of the SA (62% MVIC), and very low activation of the UT (7% MVIC) (Ekstrom et al., 2003). On the other hand, Myers et al. showed that the Scapular Punch is the exercise with the highest electromyographic (EMG) activation of the SA (66.7% MVIC), even though it generates moderate activation of the IS (35% MVIC) (Myers et al., 2005). ...
... Most of the exercises in the studies mentioned above were performed in a standing position and use excessively high loads, which are contraindicated in the early phases of treatment because they exceed the biomechanical limits of the healing tissues (Decker et al., 1999;Ekstrom et al., 2003;Hintermeister et al., 1998;Liebenson, 2012;Myers et al., 2007).To date, we have not found any publications that have analysed EMG activity of scapular and rotator cuff muscles during performance of the Supine Scapular Punch (SSP) exercise adapted for early phases. The aim of the present study is (1) to assess the excitation levels of UT, SA, and IS muscles during the performance of this exercise in the supine position in participants with and without unilateral shoulder pain (USP), and (2) to analyse whether additional load generates an increase in muscle excitability levels in both populations. ...
Article
Background Serratus anterior strengthening generally appears in shoulder rehabilitation protocols. This study's aim was to measure electromyographic activity of the serratus anterior, upper trapezius, and infraspinatus muscles during the Supine Scapular Punch exercise in healthy volunteers and those with unilateral shoulder pain. Methods Fifty-four participants were included and grouped as without (n = 34, age = 25.8 years) or with unilateral shoulder pain (n = 20, age = 26.3 years, visual analogue scale = 4.15 cm). Electromyographic activity of the serratus anterior, upper trapezius, and infraspinatus muscles was assessed during Supine Scapular Punch (four phases: P1 = press up concentric, P2 = Supine Scapular Punch concentric, P3 = Supine Scapular Punch eccentric, P4 = press up eccentric) performed under two conditions, with and without additional load. Findings Overall muscle activity during P1 and P4 was negligible (< 10% maximal voluntary isometric contractions). During P2 and P3, no statistically significant differences in serratus anterior and upper trapezius muscle activity were found between groups, with moderate to high serratus anterior activity (28.94% to 44.3%) and very low upper trapezius activity (< 6%). Upper trapezius/serratus anterior activity ratios ranged from 0.09 to 0.18. Overall infraspinatus muscle activity was always very low (< 10%). Interpretation The Supine Scapular Punch induces moderate to high serratus anterior muscle activity with very low upper trapezius and infraspinatus activation. Based on these results, the Supine Scapular Punch is a safe exercise that can be used in the early phases of shoulder rehabilitation.
... For the MVIC of the MT, the participant abducted the arm to 90°while in a prone lying position with the thumb pointing up while resistance was applied by the examiner just proximal to the elbow. 26 For the MVIC of the LT, the participant abducted the arm to approximately 140°in line with the fibers of the LT while in a prone lying position with the thumb pointing up. Resistance was applied by the examiner just proximal to the elbow. ...
... Resistance was applied by the examiner just proximal to the elbow. 26 For the MVIC of the SA, the participant flexed the shoulder 125°in the sagittal plane with full scapular protraction while seated upright. 7 Resistance was applied by the examiner just proximal to the elbow and over the lateral border of the scapula. ...
... This may be because of the more dominant role the SA compared with the LT during sagittal plane shoulder elevation [39][40][41] Second, the Flexion-EF may have involved a greater degree of horizontal adduction compared with the Flexion-EE, as participants attempted to maintain the tip of their elbow pointing forward during this exercise. Shoulder horizontal adduction in a standing position has been previously shown to increase SA activation, 26,[42][43][44] while simultaneously decrease LT activation. 42,44 This study has several limitations. ...
Article
Context: Decreased scapular upward rotation (UR) and diminished activation of the serratus anterior (SA) and lower trapezius (LT) are often observed among patients with subacromial impingement syndrome. Maintaining the elbow fully flexed during shoulder flexion may limit glenohumeral motion due to passive insufficiency of the triceps brachii and therefore facilitate greater scapular UR and increased scapular muscle activation. Objectives: To compare scapular UR, SA, upper trapezius (UT), middle trapezius, and LT activation levels between shoulder flexion with the elbow extended (Flexion-EE) to shoulder flexion with the elbow fully flexed (Flexion-EF). This study hypothesized that Flexion-EF would result in greater scapular UR, greater SA and LT activation, and a lower UT/SA and UT/LT activation ratio compared with Flexion-EE. Design: Cross-sectional study. Setting: A clinical biomechanics laboratory. Participants: Twenty-two healthy individuals. Main outcome measures: Scapular UR and electromyography signal of the SA, UT, middle trapezius, and LT, as well as UT/SA and UT/LT activation ratio were measured during Flexion-EE and Flexion-EF. Results: Flexion-EF resulted in greater scapular UR compared with Flexion-EE (P < .001). Flexion-EF resulted in greater SA activation, lower UT activation, and a lower UT/SA activation ratio compared with Flexion-EE (P < .001). Conclusions: Fully flexing the elbow during shoulder flexion leads to increased scapular UR primarily through greater activation of the SA. This exercise may be of value in circumstances involving diminished scapular UR, decreased activation of the SA, and an overly active UT such as among patients with subacromial impingement syndrome.
... В то же время флексия верхней конечности в положении лежа на здоровом боку (опционно -с утяжелителями при прогрессии тренировки), наружная ротация с утяжелением лежа на невовлеченном боку и билатеральное разгибание верхних конечностей с утяжелением лежа на животе указаны как наиболее эффективные для коррекции дисбаланса между верхней и средней порциями трапециевидной мышцы. R.A. Ekstrom с соавторами отметили наибольшую электромиографическую активность нижней порции трапециевидной мышцы при выполнении горизонтального отведения лежа на животе в сочетании с наружной ротацией (горизонтального упражнения «full can»), а также горизонтального отведения на 120° (ровно по ходу направления волокон нижней порции) [31]. По мнению M.M. Reinold, наиболее эффективным силовым упражнением, направленным на баланс сил различных пучков трапециевидной мышцы, является билатеральная наружная ротация в положении стоя при 0° отведения с резиновым эспандером перед грудной клеткой (W-exercise), акцент при этом делается на ретракции лопаток и заднем их наклоне [29] (рис. ...
... Рис. 7. Билатеральная наружная ротация в положении стоя при 0° отведения плеча с эспандером перед грудной клеткой для укрепления нижней порции трапециевидной мышцы и подостной мышцы (W-exercise) Согласно исследованиям R.A. Ekstrom с соавторами, для максимальной активности передней зубчатой мышцы необходимо обязательное сочетание протракции и верхней ротации лопатки [31]. Данные условия достигаются при выполнении упражнения «динамические удары» с резиновым эспандером и флексией 120°, когда в исходном положении пациента верхняя конечность находится в состоянии приведения, а далее осуществляются горизонтальное приведение, элевация верхней конечности и разгибание в локтевых суставах с последующей протракцией лопатки. ...
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Scapular dyskinesis is any alteration of its static position or kinematics during movements in the shoulder joint. The correct scapula orientation is associated with the tone of the muscles attached to it. The prevalence of scapular dyskinesis is high among patients with subacromial impingement syndrome, partial rotator cuff tears, shoulder joint instability and SLAP injuries. Scapular dyskinesis can be caused by a whole range of factors, including upper cross syndrome and postural adaptations predisposing to it, neurological disorders. However, instrumental diagnosis of scapular dyskinesis is difficult, which makes the use of clinical tests the main method of its detection. In this lecture, the etiology of scapular dyskinesis, classification, diagnostic tests and treatment methods are analyzed in detail. The detection of scapular dyskinesis and its type determination in patients with shoulder joint pathologies allows us to form an optimal rehabilitation therapy protocol, including techniques of myofascial release, passive and active stretching of spasmodic and training of weak muscle groups aimed at correcting postural disorders, pathology of the scapulohumeral rhythm, restoration of the glenohumeral joint normal biomechanics.
... 7 Electromyography (EMG) is a frequently used method to investigate scapular muscle activity during therapeutic exercises and could aid in suggesting recommendations for appropriate exercise selection. [16][17][18][19][20][21] Several studies have examined scapular muscle activity during elevation exercises while standing. 8,[22][23][24] But, performing shoulder elevation exercises from a prone position could be of interest for several reasons. ...
Article
Background Scapular rehabilitation exercises should target appropriate muscles. Recently, adding external rotation resistance to scapular exercises has gained interest. Moreover, clinical experts advise kinetic chain integration into shoulder rehabilitation exercises. Objective To investigate scapular muscle activity during kinetic chain variations of a prone elevation exercise. Methods Activity of the upper (UT), middle (MT), and lower (LT) trapezius and serratus anterior (SA) muscles was determined with surface electromyography (EMG) in 31 asymptomatic participants during six prone elevation exercise variations. Variation was created by adding external rotation resistance, adding trunk extension, or changing exercise position (prone on a Swiss ball with knees or feet supported, or prone on a physiotable). All data were normalized as a percentage of maximal voluntary isometric contraction (% MVIC). For each muscle, a Friedman's ANOVA was conducted to analyse statistical differences in EMG signal intensity between exercises. Results The LT was moderately (42 - 48% MVIC) and MT highly (63 - 66% MVIC) activated during all exercise variations. No significant differences between exercises for these muscles could be detected. Adding external rotation to a prone elevation exercise decreased UT activity while adding trunk extension increased UT activity. Altering exercise position had no influence on scapular muscle activity except increased UT activity when lying prone on a physiotable with trunk extension. Conclusion Prone elevation exercises are appropriate for facilitating LT and MT activity. Adding external rotation inhibits UT activity while UT facilitation could be achieved when adding trunk extension.
... Based on the result of previous studies, the appropriate position of the scapula is essential for optimal grip strength. (13) The optimum position of the scapula is maintained by the muscles attached. Thus, these muscles and their strength are ultimately responsible for hand functions. ...
Article
The human hand is designed to perform various kinds of skilled movements in the daily activities. Such activities are termed as 'Prehension Activities'. Grip strength has been used to assess general strength in order to determine work capacity, to determine the extent of injury and disease processes and progress of rehabilitation. To perform distal movements it is important to have proximal joint stability. The hand being the distal component, a good grip might require adequate shoulder stability which will be dependent upon its musculature. Hence this study was conducted to find out if there exists a correlation between these two. Aim: To find out if there is a correlation between grip strength and scapular muscles Methodology: Grip strength assessment was done using dynamometer and scapular muscle strength was assessed using Micro-FET. Results: Pearson's correlation coefficient was calculated for the correlation between grip strength and scapular muscle strength Conclusion: There is the statistically significant correlation between grip strength and scapular muscle strength
Article
BACKGROUND: Trunk muscle activity during isometric exercise is altered by external-focus instruction. OBJECTIVE: To check alterations in trunk muscle activity during side plank exercise both with and without instructions to refrain from crushing an item (external-focus instruction method). METHODS: Twenty-one healthy men aged 20–49 participated in this study. Ten trunk muscle activities were measured using surface electromyography during side plank exercises both with and without external-focus instruction. The unpaired t-test or Mann–Whitney U test was used to compare differences between exercise tasks and between sides. RESULTS: Side plank exercise with external-focus instruction increased activity of the upper trapezius, lower trapezius, latissimus dorsi, medial head of the triceps, and internal oblique on the supported side when compared with that without external-focus instruction (p< 0.05 for all). On the unsupported side, side plank exercise with external-focus instruction significantly increased activity of the upper trapezius, lower trapezius, latissimus dorsi, medial head of the triceps, clavicular part of the pectoralis major serratus anterior, external oblique, rectus abdominis, internal oblique, and multifidus when compared with that without external-focus instruction (p< 0.001 for all). CONCLUSIONS: Adding the external-focus instruction method to the conventional side plank exercise may be effective in increasing the trunk muscles’ activity.
Article
BACKGROUND: External focus isometric exercises using a paper balloon can change trunk muscle activation in the chest squeeze; however, it is unknown whether this method affects muscle activities in conventional exercises. OBJECTIVE: To check variations of trunk muscle activity during front plank (static task) and shoulder press (dynamic task) both with and without instruction to avoid crushing an object. METHODS: Twenty-six healthy adult males aged 19–49 were recruited. Ten trunk muscle activities were measured using surface electromyography during a front plank and dynamic shoulder press exercises, both with and without external-focus instruction. RESULTS: Adding the external-focus using the paper balloon to the front plank significantly activated 8 out of the 10 muscles. In the downward shoulder press, 5 out of 10 muscles with 50% 1 RM, 2 out of 10 muscles with 100% 1 RM were significantly activated. CONCLUSIONS: Adding external-focus instruction using paper-balloon increases trunk muscles in front plank and shoulder press while possibly improving trunk stability. Novel exercises using paper balloon may efficiently activate specific muscles without external loading thus possibly reducing the stress on the involved joints during exercise.
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BACKGROUND: Muscle activation during isometric contraction can be changed using an external-focus instruction method. OBJECTIVE: To explore and compare the activity of eight upper limb and trunk muscles during isometric chest squeeze exercises, performed in the same posture with and without the exertion of control to avoid crushing an object. METHODS: Muscle activation by an isometric chest squeeze with 45∘ shoulder abduction and forearm pronation was examined. Isometric chest squeeze exercises were performed while holding objects with maximum pressure, and with exerted control to avoid crushing the object Muscle activation was measured by surface electromyography. RESULTS: During the exercises performed while exerting control to avoid crushing the object the lower trapezius (p< 0.001) and latissimus dorsi (p= 0.03) showed significantly higher activity. During the exercises performed without control, the upper trapezius, serratus anterior, and pectoralis major showed significantly higher activity (p= 0.016, p< 0.001, p< 0.001, respectively). CONCLUSIONS: This novel isometric exercise can increase the scapular muscles in the intermediate range of the glenohumeral joint. Therefore, it may assist in improving sport performance, in preventing injuries and in rehabilitation following musculoskeletal injuries.
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The purpose of this study was to characterize the scapulohumeral rhythm in the normal shoulder during dynamic elevation of the arm in the scapular plane and to compare the scapulohumeral rhythm during three different states of loading: 1) arm completely unloaded and passively elevated 2) light load consisting of active elevation against the weight of the limb, and 3) heavy loading against maximal resistance. Electromagnetic tracking was used to record three-dimensional scapular and humeral kinematics on 25 normal subjects. Cardan angles were calculated to assess the dynamic relationship of humeral elevation to scapular upward rotation. The results show that during dynamic humeral elevation the scapulohumeral rhythm changes depending on the phase of elevation and the external load on the arm. During passive range of motion, the scapulohumeral rhythm decreased from 7.9:1 to 2.1:1 as the arm was elevated. li hl shoulder loads caused an increase of the scapulohumeral rhythm from 3.1:1 to 4.3:1 as the arm was elevated. Heavy shoulder loading resulted in an increasing scapulohumeral rhythm from 1.9:1 to 4.5:1 as the arm was elevated. The results suggest that the historical assumption of a simple linear 2:1 scapulohumeral rhythm ratio may be overly simplistic and may not accurately describe the scapulohumeral rhythm under varying dynamic conditions. Therapists need to understand the normal changing relationships of the scapulohumeral rhythm under different conditions for accurate interpretation of clinical observations.
Article
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Study design: Controlled laboratory study. Background: In scapular rehabilitation training, exercises that include a humeral elevation component in the scapular plane are commonly implemented. While performing humeral elevation, the scapula plays an important role, as it has to create a stable basis for the glenohumeral joint. However, a comparison of both deep and superficial muscle activity of the scapula between different types of elevation exercises is lacking and would be helpful for the clinician in choosing exercises. Objectives: To evaluate scapulothoracic muscle activity during different types of elevation exercises in the scapular plane. Methods: Scapulothoracic muscle activity was measured in 21 healthy subjects, using fine-wire electromyography in the levator scapulae, pectoralis minor, and rhomboid major muscles and surface electromyography in the upper trapezius, middle trapezius, lower trapezius, and serratus anterior muscles. Measurements were conducted while the participants performed the following elevation tasks in the scapular plane: scaption (elevation in the scapular plane), towel wall slide, and elevation with external rotation (Thera-Band). The exercises were performed without and with additional load. Possible differences between the exercises and the load were studied with a linear mixed model. Results: Performing elevation in the scapular plane with an external-rotation component resulted in higher middle trapezius and lower trapezius activity compared to the scaption and wall slide exercises. The upper trapezius was maximally activated during scaption. The pectoralis minor and serratus anterior showed the highest activity during the towel wall slide. The towel wall slide activated the retractors to a lesser degree (middle trapezius, lower trapezius, levator scapulae, rhomboid major). Adding load resulted in higher muscle activity in all muscles, with some muscles showing a different activation pattern between the elevation exercises, depending on the load condition. Conclusion: Scaption maximally activated the upper trapezius. The addition of an extra external-rotation component may be used when the goal is to activate the lower trapezius and middle trapezius. The towel wall slide exercise was found to increase pectoralis minor activity. Adding load resulted in higher muscle activity. Some muscles showed a different activation pattern between the elevation exercises, depending on the loading condition. The findings of this study give information about which elevation exercises a clinician can choose when the aim is to facilitate specific muscle scapulothoracic activity.
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This lecture explores the various uses of surface electromyography in the field of biomechanics. Three groups of applications are considered: those involving the activation timing of muscles, the force/EMG signal relationship, and the use of the EMG signal as a fatigue index. Technical considerations for recording the EMG signal with maximal fidelity are reviewed, and a compendium of all known factors that affect the information contained in the EMG signal is presented. Questions are posed to guide the practitioner in the proper use of surface electromyography. Sixteen recommendations are made regarding the proper detection, analysis, and interpretation of the EMG signal and measured force. Sixteen outstanding problems that present the greatest challenges to the advancement of surface electromyography are put forward for consideration. Finally, a plea is made for arriving at an international agreement on procedures commonly used in electromyography and biomechanics.