Accepted Manuscript Between-day reliability of a hand-held dynamometer and surface electromyography recordings during isometric submaximal contractions in different shoulder positions Kathrine S. Andersen, Birgitte H. Christensen, Afshin Samani, Pascal Madeleine PII: DOI: Reference:
S1050-6411(14)00104-7 http://dx.doi.org/10.1016/j.jelekin.2014.05.007 JJEK 1715
To appear in:
Journal of Electromyography and Kinesiology
Received Date: Revised Date: Accepted Date:
20 November 2013 22 May 2014 28 May 2014
Please cite this article as: K.S. Andersen, B.H. Christensen, A. Samani, P. Madeleine, Between-day reliability of a hand-held dynamometer and surface electromyography recordings during isometric submaximal contractions in different shoulder positions, Journal of Electromyography and Kinesiology (2014), doi: http://dx.doi.org/10.1016/ j.jelekin.2014.05.007
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Between-day reliability of a hand-held dynamometer and surface electromyography recordings during isometric submaximal contractions in different shoulder positions
Authors Kathrine S Andersen1,2, Birgitte H Christensen1,3, Afshin Samani1, Pascal Madeleine1
1: Physical Activity and Human Performance Group, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark 2: Department of Occupational and Physical Therapy, Regional Hospital Central Jutland, Viborg, Denmark 3: Department of Occupational and Physical Therapy, Aalborg University Hospital, Aalborg, Denmark
Corresponding author Prof. P. Madeleine, Ph.D., dr.scient., Physical Activity and Human Performance Group, Center for Sensory-Motor Interaction (SMI), Dept. of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7, 9220 Aalborg East, Denmark; Tel: +45994088 33. Fax: +4598154008. E-mail: [email protected]
1
1
ABSTRACT
2
Functional shoulder assessments require the use of objective and reliable standardized
3
outcome measures. Therefore, the aim of this study was to examine the between-day
4
reliability of a hand-held dynamometer when measuring muscle strength during flexion,
5
abduction, and internal and external rotation as well as surface electromyography (EMG)
6
when measuring muscle activity from m. trapezius superior and deltoideus anterior.
7
Twenty-four healthy subjects participated and performed four isometric contractions
8
measured with a hand-held dynamometer and EMG. Both relative and absolute reliability
9
were calculated based on the mean of the last three of the four repetitions. EMG amplitude
10
was assessed calculating both absolute and normalized root-mean-square (RMS) values.
11
The reliability of the hand-held dynamometer was high (LOA = 3.2%-7.6% and ICC = 0.89-
12
0.98). The absolute reliability for EMG showed similar results for absolute RMS values
13
(LOA=20.0%-68.4%) and normalized RMS values (LOA=42.4%-66.5%). However, the
14
results concerning the relative reliability showed higher ICC for absolute RMS values
15
(ICC=0.82-0.92) compared with normalized values (ICC=0.57-0.72).The outcome
16
measurements of this study with healthy subjects were found reliable and, therefore, have
17
the potential to detect changes in muscle strength and muscle activity.
18 19
Keywords: Absolute reliability, relative reliability, m. deltoideus anterior, m. trapezius
20
superior; outcome measurements.
21
2
22
1. Introduction
23
Functional shoulder assessments are performed by both researchers and clinicians. The
24
changes in performance over time are often monitored among athletes over a season and
25
among patients over interventions or treatments. The quantifications of the changes in
26
muscle strength and muscle activity around the shoulder girdle are important to assess the
27
risk of injuries among athletes (Hidalgo-Lozano et al., 2012). Patients with pain in the
28
shoulder are often characterized by lower muscle strength and muscular imbalance with
29
either weak or overactive surface electromyographic (EMG) activity (Madeleine et al.,
30
1999; Thorn et al., 2007). Especially an undesired increased EMG activity in m. trapezius
31
superior is present in patients with, e.g., rotator cuff injuries (Ludewig, 2007; Hawkes et al.,
32
2012; Cools et al., 2007). Consequently, both muscle strength and muscle activity would
33
be relevant to include as outcome measurements in studies evaluating changes in the
34
functional status of the shoulder among athletes or patients suffering from, e.g., rotator cuff
35
injuries. Prior to this, the reliability of the outcome measures needs to be addressed
36
(Atkinson and Nevill, 1998). Muscle strength can be measured with a handheld
37
dynamometer, but the positions in which the subjects are tested are in general not
38
consistent and the reported reliability fluctuates (see Table 1) (Magnusson et al., 1990;
39
Celik et al., 2012; Cadogan et al., 2011; Hayes et al., 2002). For example, Hayes et al.
40
(2002) found an intraclass correlation coefficient (ICC) of 0.85 and 0.92 for, e.g., internal
41
and external arm rotation tested with subjects in supine position and with 90o arm
42
abduction. On the other hand, Cadogan et al. tested rotation in a sitting position with 0º of
43
arm flexion and reported ICC ranging from 0.68 to 0.99 (Cadogan et al., 2011). In similar
44
test positions Cools et al. reported a relative reliability of 0.96-0.99 whereas the absolute
45
reliability showed a minimal detectable difference of 11.52-22.11 (Cools et al., 2014).
46
Many of the test positions as well as strength levels can be challenging for patients with
3
47
shoulder pain (Hayes et al., 2002). Based on these inconsistencies a reliable method is
48
required for future use in patient populations. Measurement of the EMG activity would also
49
be relevant to include for the assessment of motor control in the shoulder girdle.
50
Table 1 near here
51
Regarding EMG activity, an investigation of the reliability of different test positions is
52
required. To the best of the authors’ knowledge, EMG from m. trapezius superior and
53
deltoideus anterior has not been investigated in relatively common test positions like
54
isometric submaximal contractions and dynamic arm flexion.
55
Therefore, the aim of this study was to investigate the reliability of 1) isometric muscle
56
strength measured with a hand-held dynamometer in five different test positions when
57
performing isometric submaximal contractions and 2) EMG activity from m. trapezius
58
superior and deltoideus anterior in isometric and dynamic contractions. For that purpose,
59
we conducted a study among healthy subjects testing the between-day reliability involving
60
a handheld dynamometer and EMG recordings. The presentation of this reliability study
61
follows the guidelines for reporting reliability and agreement studies (GRRAS) (Kottner et
62
al., 2011).
63
2. Methods
64
2.1. Participants
65
The number of required subjects was estimated based on recommendations made by
66
Shoukri et al (2004) resulting in a population sample size between 18 and 29 subjects.
67
Two calculation methods were used; (i) based on the estimated ICC values, number of
68
measurements per subjects, alpha and beta level from a pilot study, and the existing
69
literature resulting in N being equal to 18 subjects and (ii) based on recommendations
70
involving the combination of the number of subjects and the number of measurements
71
made per subject resulting in N being equal to 29 subjects (Shoukri et al., 2004). Based on
4
72
these calculations, a convenient sample of 24 healthy subjects was recruited. Two
73
subjects out of 24 were left handed. The population consisted of 14 women and 10 men.
74
Mean age was 26.9 years (range 23-33 years) and mean BMI 22.9 (range 19.2-26.9). The
75
inclusion criteria were: healthy volunteers aged 18-35, ability to read and understand
76
Danish, no known neurological conditions affecting muscle strength or muscle activity, and
77
no recent surgery or pain in shoulder, neck or upper back. A questionnaire was used to
78
check if the subjects met the inclusion criterion. The study was approved by the local
79
ethical committee (N-20120040) and performed in accordance with The Declaration of
80
Helsinki. An informed consent was obtained from all subjects prior to participation. Figure 1 near here
81 82
2.2. Experimental procedure
83
All subjects were tested on their dominant shoulder by one single tester (intra-rater
84
reliability) at two occasions with 1-3 days in between (between-day reliability). See Figure
85
1A for details. The dominant shoulder was chosen since a more torque-efficient strategy is
86
reported for the dominant side (Bagesteiro and Sainburg, 2002). A hand-held Commander
87
PowerTrack II Muscle Dynamometer (PowerTrack II, JTech Medical Industries, Salt
88
Lake City, USA) was used to measure the shoulder strength in four different directions
89
(i.e., flexion, abduction, internal and external rotation). The calibration procedure had been
90
performed by the manufacturer prior to our testing. The dynamometer measures forces up
91
to 556 N with 4.4 N increments.
92
The EMG signals from m. trapezius superior and deltoideus anterior were gathered using
93
a Biovision EMG amplifier (Werheim, Germany) with the following specifications:
94
differential mode, input impedance (1200 GΩ), common mode rejection ratio (120 dB),
95
band-pass filter ([10-700 Hz]), gain (2000). The EMGs were sampled at 2000 Hz with a 12
96
bit A/D converter (input voltage +/-5 V, Biovision, Werheim, Germany) and digitally filtered
5
97
using a [10-400 Hz] band-pass filter (4th order Butterworth filter). DASYLab 10.0 software
98
(DASYLab, Norton, MA, USA) was used for data collection. Pre-gelled surface electrodes
99
(Blue Sensor M, Ambu A/S, Neuroline, Ballerup, Denmark) consisting of Ag/AgCl were
100
used. The electrodes were placed on m. trapezius superior and deltoideus anterior
101
according to recommendations made in the literature (Seitz and Uhl, 2012; Berth et al.,
102
2009;) with an inter-electrode distance of 20 mm. The electrode placement for m. trapezius
103
superior was parallel to the muscle fibres midway between processus spinosus c7 and the
104
posterior part of acromion. Electrode placement for m. deltoideus anterior was
105
approximately 3.5 cm distal and anterior of acromion (Berth et al., 2009; Meskers et al.,
106
2004; de Groot et al., 2004; Boettcher et al., 2008). A reference electrode was placed on
107
processus spinosus of C7 (see Figure 1B). Before electrode placement the skin was
108
shaved, gently abraded with fine sandpaper and wiped with alcohol to reduce the electrical
109
impedance. Adhesive tape was used as fixation of wires from the electrodes. The EMG
110
recordings started approximately 2 min after the placement of the electrodes.
111
First the subjects performed maximum voluntary isometric contractions (MVC) for m.
112
trapezius superior and deltoideus anterior. The recording sequence of MVC for the two
113
muscles was randomized in a balanced order. This was followed by a dynamic arm flexion
114
and ended with isometric submaximal contractions (see Figure 1A). The recording
115
sequence of the isometric submaximal contractions (Flexion 45o/90o, abduction 45o, and
116
internal/external rotation) was also randomized in a balanced order to avoid carry over
117
effects. EMG normalization is common when comparing subjects (McLean et al., 2003;
118
Fukuda et al., 2012). We used MVC to normalize the EMG activity (Fukuda et al., 2012;
119
Mirka, 1991), and the MVCs were performed in the following way:
120
1. MVC for m. trapezius superior was performed with the subjects standing on a
121
footstool. A non-elastic band was stretched between the footstool and the subject’s
6
122
hand. From this position the subjects were asked to perform shoulder elevation
123
(Kendall et al., 2005). See Figure 2A.
124
2. MVC for m. deltoideus anterior was performed with the subjects standing with the
125
shoulder abducted to 90o in the plane of scapula and elbow also flexed 90º. A non-
126
elastic band was fixed to a wall bar and the subject’s arm. From this position the
127
subjects were asked to perform a combination of abduction and slight flexion
128
(Kendall et al., 2005). See Figure 2A.
129
Figure 2 near here
130
The subjects performed MVC contraction lasting approximately 5 sec. and repeated four
131
times with a 30 sec. rest between each repetition (Celik et al., 2012; Cadogan et al., 2011;
132
Almosnino et al., 2009). The subjects rested for 2 min. between the MVC measured for m.
133
trapezius superior and deltoideus anterior (Jenp et al.,1996). To facilitate maximal
134
contraction and motivation, the subjects were given verbal encouragement (Samani et al.,
135
2009).
136
Dynamic arm flexion was performed while the subjects were in a standing position with the
137
dominant shoulder next to a wall. Thus the movement was performed in the sagittal plane.
138
From this position the subjects performed maximal flexion following a metronome (2 sec.
139
upward and 2 sec. downward) four times with 30 sec. rest between each repetition. Prior
140
to the recordings, the subjects practised to get acquainted with the time-paced task. See
141
Figure 2B. EMG was recorded during dynamic arm flexion.
142
The isometric submaximal contractions were performed in three directions (Figure 2C):
143
1. Flexion at 45o and 90o. The subjects were standing on a footstool with the back
144
against a wall. In a randomized order the shoulder was flexed at either 45o or 90o. A
145
non-elastic band was stretched between the footstool and the subject’s hand. From
7
146
this position the subjects were asked to perform shoulder flexion (Figure 2C a-b).
147
Both shoulder strength and EMG were recorded.
148
2. Abduction at 45o. The subjects were standing on a footstool with the back against a
149
wall. The shoulder was abducted at 45o with the elbow flexed at 90o. A non-elastic
150
band was stretched between the footstool and the subject’s elbow. From this
151
position the subjects were asked to perform shoulder abduction (Figure 2C c). Both
152
shoulder strength and EMG were recorded.
153
3. Internal and external rotation. The subjects were sitting with both feet on the ground
154
with 90o of flexion of both knees. The dominant shoulder was positioned in neutral
155
and the elbow at 90o of flexion. A non-elastic band was stretched between a wall
156
bar and the subject’s hand. From this position the subjects were asked to perform
157
an internal and external rotation of the shoulder. To avoid shoulder abduction
158
another non-elastic band was placed around the truncus and the distal end of the
159
humerus (Figure 2C d-e). Shoulder strength was recorded.
160
The subjects performed an isometric contraction lasting approximately 5 sec. and repeated
161
four times with 30 sec. rest between each repetition and for each of the movement
162
directions (McLean et al., 2003; Celik D et al., 2012; Hayes et al., 2002). The subjects
163
rested for 2 min. between each movement direction (Jenp et al.,1996).
164
2.3. Data analysis
165
Data from the hand-held dynamometer were imported into Excel 2003 (Microsoft Office©).
166
The maximum forces registered during the two MVCs and the four submaximal isometric
167
contractions were extracted. The mean of the last three contractions was used for
168
statistical analysis (Cools et al., 2014). The first repetition was considered a familiarization
169
trial, to avoid misinterpretations from initial adjustments.
8
170
Data from the EMG were analysed in Matlab (MathWorks, Natick, MA, USA), using a
171
custom-made program. The data were digitally filtered ([10-300] Hz, 4th order Butterworth
172
and Notch Filter with a width of 1 Hz at a frequency of 50 Hz). Root mean square (RMS)
173
was calculated over an epoch of 250 ms with 50% overlap between successive epochs.
174
The maximal amplitude, calculated by RMSmax, was identified. For MVC recordings, the
175
mean of RMS max over the last three repetitions was computed and used for both
176
reliability and normalization purpose. The mean of RMSmax over the last three repetitions
177
was also computed for the isometric submaximal contractions and the dynamic movement.
178
Both absolute and normalized RMS data were analysed.
179
2.4. Statistical analysis
180
Maximum force and RMSmax were used to investigate the reliability of the force and EMG
181
recordings. QQ-plot and Kolmogrov-Smirnov were used to test for normal distribution.
182
Paired t-test was used to identify significant differences between test and retest. P 0.75 was considered an acceptable reliability (Landis and Koch, 1977).
191
Statistical analyses were performed in SPSS 20.0.
and
inspected
visually
for
consistency
of
agreement.
To
test
for
Figure 3 near here
192 193 194
3. Results
9
195
3.1. Dynamometer
196
The force data were not normally distributed and, therefore, a logarithm transformation
197
was performed. No sign of heteroscedasticity was found in the log-transformed data which
198
were visually inspected by plotting the difference and mean from test and retest.
199
Furthermore, there was no statistically significant difference between test and retest
200
except from the abduction test. The results showed that the dynamometer is reliable with
201
LOA% presenting low values ranging from 3.2-7.6% and ICC ranging from 0.89-0.98
202
(Table 2, Figure 3). The visual inspection of the Bland-Altman plots (Figure 3) showed that
203
all the mean differences were close to zero and that the difference between test and retest
204
remained similar across the scale. Table 2 near here
205 206
3.2. Surface electromyography
207
The EMG data were normally distributed for the difference between test and retest.
208
Further, no sign of heteroscedasticity was found.
209
The result from MVC showed an absolute reliability of LOA% ranging from 39.4-67.1%
210
while the relative reliability showed acceptable reliability with ICC=0.79-0.86 (Table 2,
211
Figure 3).
212
Figure 4 near here
213
The results from the isometric submaximal contractions were calculated as both absolute
214
and normalized RMS values. The absolute reliability described by LOA was similar for
215
absolute (LOA=20.0%-68.4%) and normalized (LOA=42.4%-66.5%) RMS values (Table 3,
216
Figures 4 and 5). However, the results concerning the relative reliability showed higher
217
ICC for absolute (ICC=0.82-0.92) compared with normalized (ICC=0.57-0.72) RMS values
218
(Table 3, Figures 4 and 5).
219
Table 3 near here
10
220
The results from the dynamic arm movement (flexion) showed an absolute reliability of
221
LOA% ranging from 42.0%-65.6% (Table 3). The relative reliability showed acceptable
222
reliability with ICC ranging from 0.86-0.99 for absolute data and 0.89-0.96 for normalized
223
data (Table 3, Figures 4 and 5). The visual inspection of the Bland-Altman plots (Figures 4
224
and 5) revealed that all the mean differences were close to zero and that the difference
225
between test and retest tended to increase with higher level of the scale in some cases. Figure 5 near here
226 227 228
4. Discussion
229
This study showed that measurements of force in healthy subjects during isometric flexion,
230
abduction, and internal and external rotation of the shoulder by means of a hand-held
231
dynamometer are reliable in terms of both absolute and relative reliability. Further, EMG
232
recordings were also found reliable when measuring muscle activity from m. trapezius
233
superior and deltoideus anterior during isometric submaximal flexion, abduction and
234
dynamic flexion as depicted by the relative reliability. Finally, absolute RMS values were in
235
general more reliable than normalized values.
236 237
4.1. Absolute and normalized amplitude of surface electromyography signals
238
The normalization of EMG is often recommended when comparing muscle activity within
239
and between subjects (Meskers et al., 2004; McLean et al., 2003). Normalization
240
procedure is used to increase reliability by decreasing the variation between and within
241
subjects (Zakaria et al. 1996). The normalization of EMG is often made in relation to MVC
242
(Meskers et al., 2004; Fukuda et al., 2012; Marras et al., 2001). The procedure is
243
preferable when measuring static contractions (Fukuda et al., 2012) and has been found
244
suitable in the literature. Knutson et al. found that normalization using MVC showed higher
11
245
reliability when compared with normalization using mean and peak values during dynamic
246
contractions (Knutson et al., 1994). In contrast, Yang and Winter (1983) postulate that
247
MVC is not a reliable normalization procedure as the subjects’ ability to perform a MVC is
248
influenced by emotional and environmental factors. Pain can also influence the ability to
249
perform a maximal contraction questioning the use of MVC in patient populations (Meskers
250
et al., 2004). In this study, the choice of MVC is based on existing recommendations
251
(Meskers et al., 2004; Fukuda et al., 2012; Marras and Davis, 2001). Since absolute and
252
normalized data show different reliability results, other normalization procedures might be
253
appropriate. A reference contraction, such as a sub-maximal contraction or a static
254
position without external load, might be used for normalization procedures (Marras et al.,
255
2001; Yang and Winter, 1984.; Madeleine et al., 2002). If the protocol is to be used with
256
patients, the normalization procedures need to be addressed further.
257
Even though the choice of MVC in this study is based on existing recommendations, our
258
findings show different reliability values for absolute and normalized data. This
259
discrepancy was also found by Zakaria et al. (1996), who found that absolute data show
260
higher reliability compared with normalized data. The reason for these differences is
261
unknown, but might be influenced by variability in performing the MVC and the challenges
262
arising when comparing one test position with another (Zakaria et al., 1996). Furthermore,
263
the literature indicates that even though normalization is performed to reduce variability,
264
the magnitude of variance can be increased during normalization (Jackson et al., 2009 ;
265
Nordander et al., 2004).
266 267
4.2. Reliability of a hand-held dynamometer and surface electromyography
268
In this study conducted on healthy subjects, LOA shows acceptable reliability for the hand-
269
held dynamometer. However, LOA shows questionable reliability when using EMG. The
12
270
ICC shows acceptable reliability for both hand-held dynamometer and EMG. The mean
271
differences in EMG amplitude tended to increase at higher levels of the scale in some
272
cases (Figures 4 and 5), pointing at larger standard error of measurement for healthy
273
subjects with higher compared with lower EMG amplitude. Relative reliability describes the
274
degree at which subjects maintain their position in a sample with repeated measurements,
275
whereas absolute reliability is the degree at which repeated measurements vary for
276
subjects (Atkinson and Nevill, 1998). Therefore, relative reliability is affected by the ratio of
277
the variability between subjects and the total variability (Rankin and Stokes, 1998), which
278
means that heterogeneous subjects are more likely to produce a higher ICC value than
279
homogeneous subjects (Weir, 2005; de Vet et al., 2006). Absolute reliability is not affected
280
by the total variability as it is related to the difference between each subject. Our results
281
underlined the importance of reporting both absolute and relative reliability in line with
282
GRASS guidelines (Kottner, 2011).
283
Magnusson et al. (1990) indicate that a variation of 11% is to be expected when
284
measuring force signals. Therefore, the EMG variation may be altered if the 11% of
285
variation is associated with normal biological variance and not related to measurement
286
error (Magnusson et al., 1990). Despite the relatively inconsistent results concerning the
287
EMG relative and absolute reliability, the literature also shows different reliability results for
288
m. trapezius superior measured with EMG. Almosnino et al. (2009) found lower reliability
289
of isometric flexion of m. trapezius superior with ICC=0.64 and 95% confidence interval of
290
0.11-0.85. However, contrary to our study focusing on RMS values, Almosnino et al.
291
(2009) investigated EMG onset values. Nordander et al. investigated the variability of m.
292
trapezius superior in different work tasks and found low between-day variability with a
293
coefficient of variation of 8% (Nordander et al., 2004).
13
294
Since the hand-held dynamometer shows high reliability, it is relevant to include this
295
outcome measurement in future studies evaluating the functional status of the shoulder
296
among athletes or patients.
297
4.3. Clinical implications
298
In this study isometric contractions at submaximal level were investigated as these are
299
more suitable for patients compared with existing test positions (Magnusson et al., 1990;
300
Hayes et al., 2002; Forthomme et al., 2011). Patients with rotator cuff rupture often have a
301
decreased ability to stabilise the humeral head in cavitas glenoidale especially during
302
movement due to muscular loss (Ainsworth, 2006; Smith and Smith 2010; Jenp et al,
303
1996). Further, patients with rotator cuff rupture are at risk of proximal sub-luxation caused
304
by decreased ability to maintain the humeral head in the cavitas glenoidale (Ainsworth,
305
2006). This can worsen their symptoms since the subacromial space can be decreased. In
306
the literature many of the tests consisting of internal and external rotation include arm
307
abduction or flexion also resulting in decreases of the subacromial space during rotation.
308
Especially the combination of arm abduction and internal rotation is often used to provoke
309
pain in relation to shoulder impingement (Magee, 2007). Thus the test positions for internal
310
and external rotation with 0° of arm abduction or flexion used in this study may be more
311
appropriate in patients with rotator cuff tears. Furthermore, all the tests with submaximal
312
contraction were performed isometrically using a non-elastic band. In this way the subjects
313
could control the amount and rate of force development, which may also be useful with
314
patients since rapid movement may compromise the stability of the humeral head even
315
more.
316
The 45o abduction test was also performed as we hypothesized that a diminution of the
317
subacromial space. The flexion tests were performed at both 45° and 90°. Presumably, not
14
318
all patients would be able to perform 90o of flexion so it could be considered to record a
319
45° flexion only.
320
Even though the isometric contractions may be the most appropriate in patients, a
321
dynamic movement was also included in this study with the purpose of measuring the
322
interaction between m. trapezius superior and deltoideus anterior during a dynamic
323
movement. The dynamic arm movement showed acceptable relative reliability. We thus
324
suggest that the dynamic arm movement test can be used in patients since the movement
325
is performed without external load and at a low pace.
326 327
4.4 Methodological considerations
328
The measurement of force with a hand-held dynamometer reflects the sum of active
329
muscles, while the use of RMS EMG provides the researcher with recordings of muscle
330
activity from specific muscles. The present study is methodologically sound as we used a
331
randomization process in a balanced order as well as a high degree of standardization
332
concerning the performed isometric contractions. Further, blinding of subjects and
333
examiners from results of the isometric contractions was used to ensure that the examiner
334
did not influence the subjects’ performance. On the other hand, crosstalk, skin movement
335
and movement artefacts are always an issue when measuring with EMG. Even though
336
many initiatives have been made to improve existing protocols, the current study also has
337
some limitations. First, recordings from men and women were pooled even though sex
338
differences are reported in muscle coordination (Côté, 2012). There was no warm-up
339
period prior to MVCs but the participants performed a single MVC trial to become
340
familiarized with the procedure. This first MVC trial was disregarded from the analysis.
341
Moreover, the use of MVC in relation to the EMG normalization procedure may not be
15
342
appropriate in patient populations. Future studies are needed to investigate reliability in
343
patient populations.
344 345
5. Conclusions
346
The hand-held dynamometer showed high absolute and relative reliability during isometric
347
flexion, abduction, and internal and external rotation among healthy subjects. Further, the
348
EMG showed acceptable relative reliability when measuring muscle activity from m.
349
trapezius superior and deltoideus anterior in isometric submaximal flexion, abduction and
350
a dynamic arm movement. Therefore, the outcome measurements have the potential to
351
detect changes in muscle strength and muscle activity. The current protocol may be used
352
in patient populations but the use of normalization with respect to MVC can be
353
problematic.
354 355
Acknowledgements
356
This study was partly supported by a grant from Gigtforeningen (The Danish Rheumatism
357
Association).
358 359
Conflict of interests
360
There is no conflict of interests from any of the authors.
361
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Knutson LM, Soderberg GL, Ballantyne BT, Clarke WR. A study of various normalization procedures for within day electromyographic data. J Electromyogr Kinesiol 1994;4:47–59. Kottner J, Audigé L, Brorson S, Donner A, Gajewski BJ, Hróbjartsson A, Roberts C, Shoukri M, Streinser DL. Guidelines for Reporting Reliability and Agreement Studies (GRRAS) were proposed. J Clin Epidemiol 2001;64:96– 106. Landis JR, Koch G. The measurement of observer agreement for categorical data. Biometrics 1977;33:159–74. Ludewig PM, Reynolds JF. The association of scapular kinematics and glenohumeral joint pathologie. J Orthop Sports Phys Ther 2007;39:90–104. Madeleine P, Farina D, Merletti R, Arendt-Nielsen L. Normalisation effects of the upper trapezius mechanomyographic and electromyographic activity during test and fatiguing contraction. Eur J Applied Physiol 2002;87:327–36. Madeleine P, Lundager B, Voigt M, Arendt-Nielsen L. Shoulder muscle coordination under chronic and experimental neck-shoulder pain. An occupational pain study. Eur J Appl Occup Physiol1999;79:127–40. Magee DJ. Orthopedic physical assessment. 5th ed. Saunders Elsevier;2007. Magnusson SP, Gleim GW, Nicholas JA. Subject variability of strength testing shoulder abduction. Am J Sports Med 1990;18:349–53. Marras WS, Davis KG. A non-MVC EMG normalization technique for the trunk musculature: Part 1. Method development. J Electromyogr Kinesiol 2001;11:1–9. McLean L, Chislett M, Keith M, Murphy M, Walton P. The effect of head position , electrode site , movement and smoothing window in the determination of a reliable maximum voluntary activation of the upper trapezius muscle. J Electromyogr Kinesiol 2003;13:169–80. Meskers CG, de Groot JH, Arwert HJ, Rozendaal LA, Rozing M. Reliability of force direction dependent EMG parameters of shoulder muscles for clinical measurements. Clin Biomech 2004;19:913–20. Mirka GA. The quantification of EMG normalization error. Ergonomics 1991;34:343–52. Nordander C, Balogh I, Mathiassen SE, Ohlsson K, Unge J, Skerfving S, Hansson GA. Precision of measurements of physical workload during standardised
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manual handling. Part I: surface electromyography of m. trapezius, m. infraspinatus and the forearm extensors. J Electromyogr Kinesiology 2004;14:443–54. Rankin G, Stokes M. Reliability of assessment tools in rehabilitation: an illustration of appropriate statistical analyses. Clin Rehabil 1998;12:187–99. Samani A, Holtermann A, Søgaard K, Madeleine P. Effects of eccentric exercise on trapezius electromyography during computer work with active and passive pauses. Clin Biomech 2009;24:619–25. Seitz AL, Uhl TL. Reliability and minimal detectable change in scapulothoracic neuromuscular activity. J Electromyogr Kinesiol 2012;22:968–74. Shoukri MM, Asyali MH, Donner A. Sample size requirements for the design of reliability study: review and new results. Statistical Methods Med Res 2004;13:251–71. Smith MA, Smith WT. Rotator cuff tears: an overview. Orthop Nurs 2010;29:319– 22. Steenbrink F, de Groot JH, Veeger HE, Meskers CG, van de Sande MA, Rozing PM. Pathological muscle activation patterns in patients with massive rotator cuff tears, with and without subacromial anaesthetics. Man Ther 2006;11:231–7. Thorn S, Søgaard K, Kallenberg LA, Sandsjö L, Sjøgaard G, Hermens HJ, Kadefors R, Forsman M. Trapezius muscle rest time during standardised computer work - A comparison of female computer users with and without self-reported neck/shoulder complaints. J Electromyogr Kinesiol 2007;17:420–27. de Vet H, Terwee CB, Knol DL, Bouter LM. When to use agreement versus reliability measures. J Clin Epidemiol 2006;59:1033–39. Weir JP. Quantifying rest-retest reliability using the intraclass correlation coefficient and the SEM. J Stength Cond Res 2005;19:231–40. Yang JF, Winter DA. Electromyographic amplitude normalization methods: improving their sensitivity as diagnostic tools in gait analysis. Arch Phys Med Rehabil 1984;65:517–521. Yang JF, Winther DA. Electromyography reliability in maximal and submaximal isometric contractions. Arch Phys Med Rehabil 1983;64:417–20.
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Zakaria D, Kramer JF, Harburn KL. Reliability of non-normalized and normalized integrated EMG during maximal isometric contractions in females. J Electromyogr Kinesiol 1996;6:129–35.
21
Table 1: Description and reliability results from studies using strength measured with a handheld dynamometer as outcome measure. Study
Test positions o
Magnusson
90 abduction with manual resistance.
et al. 1990.
Shoulder
Movement
n
Reliability
Non-dominant. The
Isometric
9
r = 0.94-0.98
Isometric
8-
ICC = 0.96¹, 0.92²
dominant shoulder was tested with an isokinetic machine. o
Hayes et al. Elevation with 90 flexion in the plane of scapula (30 2002.
o
Symptomatic shoulder
frontal).
9* o
External rotation in supine position with 90 arm
ICC = 0.92¹, 0.82²
abduction. Internal rotation in supine position with 90o arm
ICC = 0.85¹´²
abduction. Lift-off from lumbal spine.
ICC = 0.70¹, 0.79²
Celik et al. Test of specific muscles, among these
Dominant and non-
2012.
dominant
- m. trapezius superior during elevation of the shoulder
Isometric
o
- m. deltoideus anterior during 90 flexion of the arm Cadogan
et
o
Abduction 10 in the plane of scapula.
al. 2011.
Symptomatic and asymptomatic shoulder
External rotation during sitting.
Isometric
35 +
ICC = 0.45-0.97
22*
ICC = 0.72-0.95
40*
ICC = 0.91-0.98¹, 0.77-0.84² LOA = 2.2-7¹, 6.3-8.5²
ICC = 0.91-0.99¹, 0.68-0.74² LOA = 1.1-3.2¹, 3.2-4.4²
22
Cools et al. Test of internal and external rotation in different 2014.
Not mentioned
Isometric
30
shoulder and patient positions. Internal rotation in sitting position with 0 o abduction.
ICC = 0.96-0.99¹, 0.98²
MDC= 14.07-22.11¹, 7.76² External rotation in sitting position with 0 o abduction.
ICC = 0.96-0.97¹, 0.96² MDC = 11.52-12.80¹, 6.00²
Abbreviations: * refer to subjects with shoulder pain, ¹ refer to intra-rater reliability and ² refer to inter-rater reliability.
23
Table 2. The relative and absolute reliability of the m. trapezius superior (TS) and m. deltoideus anterior (DA) root mean square during maximum voluntary contraction and of the hand-held dynamometer during isometric contractions. ICC (95% CI)
LOA (95% CI)
LOA %
Maximum voluntary contraction
TS
0.86 (0.70-0.94)
0.36 (-0.30-0.43)
67.1%
DA
0.79 (0.48-0.91)
0.86 (-1.13-0.58)
39.4%
Flexion 45o
0.91 (0.81-0.96)
0.14 (-0.13-0.15)
7.6%
Flexion 90o
0.91 (0.79-0.96)
0.14 (-0.13-0.14)
7.3%
Abduction
0.94 (0.85-0.98)
0.10 (-0.07-0.12)
4.5%
Internal rotation
0.98 (0.95-0.99)
0.07 (-0.07-0.07)
3.2%
External rotation
0.89 (0.76-0.95)
0.12 (-0.12-0.13)
6.4%
Isometric contractions
Abbreviations: ICC: Intraclass correlation coefficient, LOA: Limits of agreement, CI: confidence interval.
24
Table 3. The relative and absolute reliability of the absolute and normalized surface electromyography (EMG) root mean square recorded from the m. trapezius superior (TS) and m. deltoideus anterior (DA) during isometric and dynamic contractions. ICC Absolute EMG
ICC Normalized EMG
LOA Absolute EMG
LOA Normalized EMG
LOA %
LOA %
(95% CI)
(95% CI)
(95% CI)
(95% CI)
Absolute EMG
Normalized EMG
Flexion 45o TS
0.88 (0.71-0.95)
0.72 (0.46-0.87)
0.25 (-0.19-0.31)
40.31 (-37.82-42.79)
59.1%
48.2%
Flexion 45o DA
0.88 (0.73-0.94)
0.57 (0.22-0.79)
0.70 (-0.68-0.72)
69.28 (-52.35-86.22)
26.0%
52.5%
Flexion 90o TS
0.82 (0.63-0.92)
0.60 (0.27-0.80)
0.33 (-0.34-0.32)
67.33 (-80.53-54.13)
68.4%
66.5%
Flexion 90o DA
0.92 (0.83-0.96)
0.59 (0.26-0.80)
0.55 (-0.60-0.49)
70.34 (-56.44-84.25)
20.0%
52.2%
Abduction TS
0.90 (0.79-0.96)
0.72 (0.46-0.87)
0.30 (-0.27-0.33)
49.48 (-55.98-42.98)
52.8%
42.4%
Abduction DA
0.89 (0.76-0.95)
0.63 (0.31-0.82)
0.67 (-0.72-0.61)
70.79 (-55.42-86.16)
22.7%
49.0%
Isometric contractions
Dynamic contractions
Dynamic TS
0.99 (0.97-0.99)
0.96 (0.91-0.98)
0.12 (-0.10-0.14)
19.91 (-21.61-18.21)
65.6%
55.9%
Dynamic DA
0.86 (0.71-0.94)
0.89 (0.86-0.97)
0.63 (-0.50-0.77)
32.79 (-20.72-44.86)
42.0%
50.4%
Abbreviations: ICC: Intraclass correlation coefficient, CI: confidence interval, LOA: Limits of agreement
25
Fig. 1. A. Design of the test procedure. The procedure was repeated with 1-3 days in between. MVC = maximum voluntary isometric contraction. TS: m. trapezius superior, DA: m. deltoideus anterior. Four isometric contractions were performed in flexion, abduction, and with internal and external rotation. See Methods section for further details. B. Electrode placement for m. trapezius superior and m. deltoideus anterior. Fig. 2. Performance of maximum voluntary isometric contraction (MVC) and isometric submaximal contractions. A: MVC performed for m. trapezius superior and m. deltoideus anterior. B: Dynamic arm flexion. C: Isometric submaximal contractions. a=flexion at 45°, b=flexion at 90°, c=abduction at 45°, d=internal rotation, e=external rotation. Fig. 3. Bland-Altman plots for test-retest reliability of the absolute root mean square values recorded from m. trapezius superior and m. deltoideus anterior during maximum voluntary isometric contraction and of the hand-held dynamometer isometric contractions. Fig. 4. Bland-Altman plots for test-retest reliability of the absolute and normalized root mean square values recorded from m. trapezius superior during isometric and dynamic contractions. Fig. 5. Bland-Altman plots for test-retest reliability of the absolute and normalized root mean square values recorded from m. deltoideus anterior during isometric and dynamic contractions.
26
Figure
Figure 1
4 x isometric maximum contractions 5 sec.
Submaximal dynamic and isometric contractions
Dynamic arm flexion 2 sec. upward & 2 sec. downward
2 min rest
Maximum voluntary contraction
2 min rest
A
Isometric contractions
5 sec. 30 sec. rest in between repetition 2 min. rest between each direction
30 sec. rest in between repetition 2 min. rest between TS and DA MVC
Procedure repeated after 1-3 days
B
Electrode placement for m. trapezius superior
Electrode placement for m. deltoideus anterior
Figure 2
A: Maximum voluntary contraction for respectively m. trapezius and m. deltoideus anterior
B: Dynamic arm flexion
C: Isometric test contractions. a : 45o arm flexion, b : 90o arm flexion, c :45o arm abduction, d : internal arm rotation, and e: external arm rotation
Figure 3 Maximum voluntary contraction
Isometric contractions – Hand-held dynamometer Flexion 45o
Flexion 90o
Difference between test and retest
Difference between test and retest
m. trapezius superior
Difference between test and retest
Abduction
Internal rotation
Exernal rotation
Difference between test and retest
Difference between test and retest
m. deltoideus anterior
Mean of test and retest
Mean of test and retest
Mean of test and retest
Figure 4 Isometric contractions Flexion 90o
Abduction
Difference between test and retest
Flexion 45o
Dynamic contraction
Difference between test and retest
Absolute root mean square values from m. trapezius superior
Mean of test and retest
Mean of test and retest
Mean of test and retest
Normalized root mean square values from m. trapezius superior
Mean of test and retest
Figure 5 Isometric contractions Flexion 90o
Abduction
Difference between test and retest
Flexion 45o
Dynamic contraction
Difference between test and retest
Absolute root mean square values from m. deltoideus anterior
Mean of test and retest
Mean of test and retest
Mean of test and retest
Normalized root mean square values from m. deltoideus anterior
Mean of test and retest
Kathrine S Andersen received her degree as a physiotherapist in 2011 from University College Nordjylland and her Master of Science in Clinical Science and Technology from Aalborg University in 2013. She is currently employed at Viborg Region Hospital as a physiotherapist with responsibility for development and research of clinical practice in the field of neurology. Furthermore she is employed as a research physiotherapist at Aalborg University Hospital, where her research field is patients with shoulder pain and altered kinematics.
Birgitte H Christensen received her degree as a physiotherapist in 2011 from University College Nordjylland and her Master of Science in Clinical Science and Technology from Aalborg University in 2013. She is currently employed at Aalborg University Hospital as a physiotherapist with responsibility for development and research of clinical practice in the field of neurology, pediatrics and neurosurgery. Furthermore she is employed as a research physiotherapist at Aalborg University Hospital, where her research field is patients with shoulder pain and altered kinematics.
Afshin Samani received his PhD in Biomedical Engineering and Science in 2010 from Aalborg University, Denmark. He is currently employed as an assistant professor in sports science and ergonomics at the Department of Health Science and Technology at Aalborg University, Denmark. He is co-director of the laboratory for Ergonomics and Work-related Disorders. His specific research field is focused on methods of quantification of work exposure, risk factors for the development of musculoskeletal disorders and interactions between muscle pain and motor control among computer users. Pascal Madeleine was born in Toulouse, France, in 1969. He received his Dr. Scient. degree and PhD from Aalborg University, Denmark. He is currently employed as a Professor at the Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology at Aalborg University, Denmark. He is head of the research interest group within Physical Activity and Human Performance and co-director of the laboratory for Ergonomics and Work-related Disorders. He has published more 130 peer reviewed scientific journal publications and book chapters. His main area of research interests are the development and application of novel methods and technologies in Ergonomics and Sports.
27
Kathrine S Andersen
Birgitte H Christensen
Afshin Samani
Pascal Madeleine
28
S1050-6411(14)00104-7 http://dx.doi.org/10.1016/j.jelekin.2014.05.007 JJEK 1715
To appear in:
Journal of Electromyography and Kinesiology
Received Date: Revised Date: Accepted Date:
20 November 2013 22 May 2014 28 May 2014
Please cite this article as: K.S. Andersen, B.H. Christensen, A. Samani, P. Madeleine, Between-day reliability of a hand-held dynamometer and surface electromyography recordings during isometric submaximal contractions in different shoulder positions, Journal of Electromyography and Kinesiology (2014), doi: http://dx.doi.org/10.1016/ j.jelekin.2014.05.007
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Between-day reliability of a hand-held dynamometer and surface electromyography recordings during isometric submaximal contractions in different shoulder positions
Authors Kathrine S Andersen1,2, Birgitte H Christensen1,3, Afshin Samani1, Pascal Madeleine1
1: Physical Activity and Human Performance Group, Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark 2: Department of Occupational and Physical Therapy, Regional Hospital Central Jutland, Viborg, Denmark 3: Department of Occupational and Physical Therapy, Aalborg University Hospital, Aalborg, Denmark
Corresponding author Prof. P. Madeleine, Ph.D., dr.scient., Physical Activity and Human Performance Group, Center for Sensory-Motor Interaction (SMI), Dept. of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7, 9220 Aalborg East, Denmark; Tel: +45994088 33. Fax: +4598154008. E-mail: [email protected]
1
1
ABSTRACT
2
Functional shoulder assessments require the use of objective and reliable standardized
3
outcome measures. Therefore, the aim of this study was to examine the between-day
4
reliability of a hand-held dynamometer when measuring muscle strength during flexion,
5
abduction, and internal and external rotation as well as surface electromyography (EMG)
6
when measuring muscle activity from m. trapezius superior and deltoideus anterior.
7
Twenty-four healthy subjects participated and performed four isometric contractions
8
measured with a hand-held dynamometer and EMG. Both relative and absolute reliability
9
were calculated based on the mean of the last three of the four repetitions. EMG amplitude
10
was assessed calculating both absolute and normalized root-mean-square (RMS) values.
11
The reliability of the hand-held dynamometer was high (LOA = 3.2%-7.6% and ICC = 0.89-
12
0.98). The absolute reliability for EMG showed similar results for absolute RMS values
13
(LOA=20.0%-68.4%) and normalized RMS values (LOA=42.4%-66.5%). However, the
14
results concerning the relative reliability showed higher ICC for absolute RMS values
15
(ICC=0.82-0.92) compared with normalized values (ICC=0.57-0.72).The outcome
16
measurements of this study with healthy subjects were found reliable and, therefore, have
17
the potential to detect changes in muscle strength and muscle activity.
18 19
Keywords: Absolute reliability, relative reliability, m. deltoideus anterior, m. trapezius
20
superior; outcome measurements.
21
2
22
1. Introduction
23
Functional shoulder assessments are performed by both researchers and clinicians. The
24
changes in performance over time are often monitored among athletes over a season and
25
among patients over interventions or treatments. The quantifications of the changes in
26
muscle strength and muscle activity around the shoulder girdle are important to assess the
27
risk of injuries among athletes (Hidalgo-Lozano et al., 2012). Patients with pain in the
28
shoulder are often characterized by lower muscle strength and muscular imbalance with
29
either weak or overactive surface electromyographic (EMG) activity (Madeleine et al.,
30
1999; Thorn et al., 2007). Especially an undesired increased EMG activity in m. trapezius
31
superior is present in patients with, e.g., rotator cuff injuries (Ludewig, 2007; Hawkes et al.,
32
2012; Cools et al., 2007). Consequently, both muscle strength and muscle activity would
33
be relevant to include as outcome measurements in studies evaluating changes in the
34
functional status of the shoulder among athletes or patients suffering from, e.g., rotator cuff
35
injuries. Prior to this, the reliability of the outcome measures needs to be addressed
36
(Atkinson and Nevill, 1998). Muscle strength can be measured with a handheld
37
dynamometer, but the positions in which the subjects are tested are in general not
38
consistent and the reported reliability fluctuates (see Table 1) (Magnusson et al., 1990;
39
Celik et al., 2012; Cadogan et al., 2011; Hayes et al., 2002). For example, Hayes et al.
40
(2002) found an intraclass correlation coefficient (ICC) of 0.85 and 0.92 for, e.g., internal
41
and external arm rotation tested with subjects in supine position and with 90o arm
42
abduction. On the other hand, Cadogan et al. tested rotation in a sitting position with 0º of
43
arm flexion and reported ICC ranging from 0.68 to 0.99 (Cadogan et al., 2011). In similar
44
test positions Cools et al. reported a relative reliability of 0.96-0.99 whereas the absolute
45
reliability showed a minimal detectable difference of 11.52-22.11 (Cools et al., 2014).
46
Many of the test positions as well as strength levels can be challenging for patients with
3
47
shoulder pain (Hayes et al., 2002). Based on these inconsistencies a reliable method is
48
required for future use in patient populations. Measurement of the EMG activity would also
49
be relevant to include for the assessment of motor control in the shoulder girdle.
50
Table 1 near here
51
Regarding EMG activity, an investigation of the reliability of different test positions is
52
required. To the best of the authors’ knowledge, EMG from m. trapezius superior and
53
deltoideus anterior has not been investigated in relatively common test positions like
54
isometric submaximal contractions and dynamic arm flexion.
55
Therefore, the aim of this study was to investigate the reliability of 1) isometric muscle
56
strength measured with a hand-held dynamometer in five different test positions when
57
performing isometric submaximal contractions and 2) EMG activity from m. trapezius
58
superior and deltoideus anterior in isometric and dynamic contractions. For that purpose,
59
we conducted a study among healthy subjects testing the between-day reliability involving
60
a handheld dynamometer and EMG recordings. The presentation of this reliability study
61
follows the guidelines for reporting reliability and agreement studies (GRRAS) (Kottner et
62
al., 2011).
63
2. Methods
64
2.1. Participants
65
The number of required subjects was estimated based on recommendations made by
66
Shoukri et al (2004) resulting in a population sample size between 18 and 29 subjects.
67
Two calculation methods were used; (i) based on the estimated ICC values, number of
68
measurements per subjects, alpha and beta level from a pilot study, and the existing
69
literature resulting in N being equal to 18 subjects and (ii) based on recommendations
70
involving the combination of the number of subjects and the number of measurements
71
made per subject resulting in N being equal to 29 subjects (Shoukri et al., 2004). Based on
4
72
these calculations, a convenient sample of 24 healthy subjects was recruited. Two
73
subjects out of 24 were left handed. The population consisted of 14 women and 10 men.
74
Mean age was 26.9 years (range 23-33 years) and mean BMI 22.9 (range 19.2-26.9). The
75
inclusion criteria were: healthy volunteers aged 18-35, ability to read and understand
76
Danish, no known neurological conditions affecting muscle strength or muscle activity, and
77
no recent surgery or pain in shoulder, neck or upper back. A questionnaire was used to
78
check if the subjects met the inclusion criterion. The study was approved by the local
79
ethical committee (N-20120040) and performed in accordance with The Declaration of
80
Helsinki. An informed consent was obtained from all subjects prior to participation. Figure 1 near here
81 82
2.2. Experimental procedure
83
All subjects were tested on their dominant shoulder by one single tester (intra-rater
84
reliability) at two occasions with 1-3 days in between (between-day reliability). See Figure
85
1A for details. The dominant shoulder was chosen since a more torque-efficient strategy is
86
reported for the dominant side (Bagesteiro and Sainburg, 2002). A hand-held Commander
87
PowerTrack II Muscle Dynamometer (PowerTrack II, JTech Medical Industries, Salt
88
Lake City, USA) was used to measure the shoulder strength in four different directions
89
(i.e., flexion, abduction, internal and external rotation). The calibration procedure had been
90
performed by the manufacturer prior to our testing. The dynamometer measures forces up
91
to 556 N with 4.4 N increments.
92
The EMG signals from m. trapezius superior and deltoideus anterior were gathered using
93
a Biovision EMG amplifier (Werheim, Germany) with the following specifications:
94
differential mode, input impedance (1200 GΩ), common mode rejection ratio (120 dB),
95
band-pass filter ([10-700 Hz]), gain (2000). The EMGs were sampled at 2000 Hz with a 12
96
bit A/D converter (input voltage +/-5 V, Biovision, Werheim, Germany) and digitally filtered
5
97
using a [10-400 Hz] band-pass filter (4th order Butterworth filter). DASYLab 10.0 software
98
(DASYLab, Norton, MA, USA) was used for data collection. Pre-gelled surface electrodes
99
(Blue Sensor M, Ambu A/S, Neuroline, Ballerup, Denmark) consisting of Ag/AgCl were
100
used. The electrodes were placed on m. trapezius superior and deltoideus anterior
101
according to recommendations made in the literature (Seitz and Uhl, 2012; Berth et al.,
102
2009;) with an inter-electrode distance of 20 mm. The electrode placement for m. trapezius
103
superior was parallel to the muscle fibres midway between processus spinosus c7 and the
104
posterior part of acromion. Electrode placement for m. deltoideus anterior was
105
approximately 3.5 cm distal and anterior of acromion (Berth et al., 2009; Meskers et al.,
106
2004; de Groot et al., 2004; Boettcher et al., 2008). A reference electrode was placed on
107
processus spinosus of C7 (see Figure 1B). Before electrode placement the skin was
108
shaved, gently abraded with fine sandpaper and wiped with alcohol to reduce the electrical
109
impedance. Adhesive tape was used as fixation of wires from the electrodes. The EMG
110
recordings started approximately 2 min after the placement of the electrodes.
111
First the subjects performed maximum voluntary isometric contractions (MVC) for m.
112
trapezius superior and deltoideus anterior. The recording sequence of MVC for the two
113
muscles was randomized in a balanced order. This was followed by a dynamic arm flexion
114
and ended with isometric submaximal contractions (see Figure 1A). The recording
115
sequence of the isometric submaximal contractions (Flexion 45o/90o, abduction 45o, and
116
internal/external rotation) was also randomized in a balanced order to avoid carry over
117
effects. EMG normalization is common when comparing subjects (McLean et al., 2003;
118
Fukuda et al., 2012). We used MVC to normalize the EMG activity (Fukuda et al., 2012;
119
Mirka, 1991), and the MVCs were performed in the following way:
120
1. MVC for m. trapezius superior was performed with the subjects standing on a
121
footstool. A non-elastic band was stretched between the footstool and the subject’s
6
122
hand. From this position the subjects were asked to perform shoulder elevation
123
(Kendall et al., 2005). See Figure 2A.
124
2. MVC for m. deltoideus anterior was performed with the subjects standing with the
125
shoulder abducted to 90o in the plane of scapula and elbow also flexed 90º. A non-
126
elastic band was fixed to a wall bar and the subject’s arm. From this position the
127
subjects were asked to perform a combination of abduction and slight flexion
128
(Kendall et al., 2005). See Figure 2A.
129
Figure 2 near here
130
The subjects performed MVC contraction lasting approximately 5 sec. and repeated four
131
times with a 30 sec. rest between each repetition (Celik et al., 2012; Cadogan et al., 2011;
132
Almosnino et al., 2009). The subjects rested for 2 min. between the MVC measured for m.
133
trapezius superior and deltoideus anterior (Jenp et al.,1996). To facilitate maximal
134
contraction and motivation, the subjects were given verbal encouragement (Samani et al.,
135
2009).
136
Dynamic arm flexion was performed while the subjects were in a standing position with the
137
dominant shoulder next to a wall. Thus the movement was performed in the sagittal plane.
138
From this position the subjects performed maximal flexion following a metronome (2 sec.
139
upward and 2 sec. downward) four times with 30 sec. rest between each repetition. Prior
140
to the recordings, the subjects practised to get acquainted with the time-paced task. See
141
Figure 2B. EMG was recorded during dynamic arm flexion.
142
The isometric submaximal contractions were performed in three directions (Figure 2C):
143
1. Flexion at 45o and 90o. The subjects were standing on a footstool with the back
144
against a wall. In a randomized order the shoulder was flexed at either 45o or 90o. A
145
non-elastic band was stretched between the footstool and the subject’s hand. From
7
146
this position the subjects were asked to perform shoulder flexion (Figure 2C a-b).
147
Both shoulder strength and EMG were recorded.
148
2. Abduction at 45o. The subjects were standing on a footstool with the back against a
149
wall. The shoulder was abducted at 45o with the elbow flexed at 90o. A non-elastic
150
band was stretched between the footstool and the subject’s elbow. From this
151
position the subjects were asked to perform shoulder abduction (Figure 2C c). Both
152
shoulder strength and EMG were recorded.
153
3. Internal and external rotation. The subjects were sitting with both feet on the ground
154
with 90o of flexion of both knees. The dominant shoulder was positioned in neutral
155
and the elbow at 90o of flexion. A non-elastic band was stretched between a wall
156
bar and the subject’s hand. From this position the subjects were asked to perform
157
an internal and external rotation of the shoulder. To avoid shoulder abduction
158
another non-elastic band was placed around the truncus and the distal end of the
159
humerus (Figure 2C d-e). Shoulder strength was recorded.
160
The subjects performed an isometric contraction lasting approximately 5 sec. and repeated
161
four times with 30 sec. rest between each repetition and for each of the movement
162
directions (McLean et al., 2003; Celik D et al., 2012; Hayes et al., 2002). The subjects
163
rested for 2 min. between each movement direction (Jenp et al.,1996).
164
2.3. Data analysis
165
Data from the hand-held dynamometer were imported into Excel 2003 (Microsoft Office©).
166
The maximum forces registered during the two MVCs and the four submaximal isometric
167
contractions were extracted. The mean of the last three contractions was used for
168
statistical analysis (Cools et al., 2014). The first repetition was considered a familiarization
169
trial, to avoid misinterpretations from initial adjustments.
8
170
Data from the EMG were analysed in Matlab (MathWorks, Natick, MA, USA), using a
171
custom-made program. The data were digitally filtered ([10-300] Hz, 4th order Butterworth
172
and Notch Filter with a width of 1 Hz at a frequency of 50 Hz). Root mean square (RMS)
173
was calculated over an epoch of 250 ms with 50% overlap between successive epochs.
174
The maximal amplitude, calculated by RMSmax, was identified. For MVC recordings, the
175
mean of RMS max over the last three repetitions was computed and used for both
176
reliability and normalization purpose. The mean of RMSmax over the last three repetitions
177
was also computed for the isometric submaximal contractions and the dynamic movement.
178
Both absolute and normalized RMS data were analysed.
179
2.4. Statistical analysis
180
Maximum force and RMSmax were used to investigate the reliability of the force and EMG
181
recordings. QQ-plot and Kolmogrov-Smirnov were used to test for normal distribution.
182
Paired t-test was used to identify significant differences between test and retest. P 0.75 was considered an acceptable reliability (Landis and Koch, 1977).
191
Statistical analyses were performed in SPSS 20.0.
and
inspected
visually
for
consistency
of
agreement.
To
test
for
Figure 3 near here
192 193 194
3. Results
9
195
3.1. Dynamometer
196
The force data were not normally distributed and, therefore, a logarithm transformation
197
was performed. No sign of heteroscedasticity was found in the log-transformed data which
198
were visually inspected by plotting the difference and mean from test and retest.
199
Furthermore, there was no statistically significant difference between test and retest
200
except from the abduction test. The results showed that the dynamometer is reliable with
201
LOA% presenting low values ranging from 3.2-7.6% and ICC ranging from 0.89-0.98
202
(Table 2, Figure 3). The visual inspection of the Bland-Altman plots (Figure 3) showed that
203
all the mean differences were close to zero and that the difference between test and retest
204
remained similar across the scale. Table 2 near here
205 206
3.2. Surface electromyography
207
The EMG data were normally distributed for the difference between test and retest.
208
Further, no sign of heteroscedasticity was found.
209
The result from MVC showed an absolute reliability of LOA% ranging from 39.4-67.1%
210
while the relative reliability showed acceptable reliability with ICC=0.79-0.86 (Table 2,
211
Figure 3).
212
Figure 4 near here
213
The results from the isometric submaximal contractions were calculated as both absolute
214
and normalized RMS values. The absolute reliability described by LOA was similar for
215
absolute (LOA=20.0%-68.4%) and normalized (LOA=42.4%-66.5%) RMS values (Table 3,
216
Figures 4 and 5). However, the results concerning the relative reliability showed higher
217
ICC for absolute (ICC=0.82-0.92) compared with normalized (ICC=0.57-0.72) RMS values
218
(Table 3, Figures 4 and 5).
219
Table 3 near here
10
220
The results from the dynamic arm movement (flexion) showed an absolute reliability of
221
LOA% ranging from 42.0%-65.6% (Table 3). The relative reliability showed acceptable
222
reliability with ICC ranging from 0.86-0.99 for absolute data and 0.89-0.96 for normalized
223
data (Table 3, Figures 4 and 5). The visual inspection of the Bland-Altman plots (Figures 4
224
and 5) revealed that all the mean differences were close to zero and that the difference
225
between test and retest tended to increase with higher level of the scale in some cases. Figure 5 near here
226 227 228
4. Discussion
229
This study showed that measurements of force in healthy subjects during isometric flexion,
230
abduction, and internal and external rotation of the shoulder by means of a hand-held
231
dynamometer are reliable in terms of both absolute and relative reliability. Further, EMG
232
recordings were also found reliable when measuring muscle activity from m. trapezius
233
superior and deltoideus anterior during isometric submaximal flexion, abduction and
234
dynamic flexion as depicted by the relative reliability. Finally, absolute RMS values were in
235
general more reliable than normalized values.
236 237
4.1. Absolute and normalized amplitude of surface electromyography signals
238
The normalization of EMG is often recommended when comparing muscle activity within
239
and between subjects (Meskers et al., 2004; McLean et al., 2003). Normalization
240
procedure is used to increase reliability by decreasing the variation between and within
241
subjects (Zakaria et al. 1996). The normalization of EMG is often made in relation to MVC
242
(Meskers et al., 2004; Fukuda et al., 2012; Marras et al., 2001). The procedure is
243
preferable when measuring static contractions (Fukuda et al., 2012) and has been found
244
suitable in the literature. Knutson et al. found that normalization using MVC showed higher
11
245
reliability when compared with normalization using mean and peak values during dynamic
246
contractions (Knutson et al., 1994). In contrast, Yang and Winter (1983) postulate that
247
MVC is not a reliable normalization procedure as the subjects’ ability to perform a MVC is
248
influenced by emotional and environmental factors. Pain can also influence the ability to
249
perform a maximal contraction questioning the use of MVC in patient populations (Meskers
250
et al., 2004). In this study, the choice of MVC is based on existing recommendations
251
(Meskers et al., 2004; Fukuda et al., 2012; Marras and Davis, 2001). Since absolute and
252
normalized data show different reliability results, other normalization procedures might be
253
appropriate. A reference contraction, such as a sub-maximal contraction or a static
254
position without external load, might be used for normalization procedures (Marras et al.,
255
2001; Yang and Winter, 1984.; Madeleine et al., 2002). If the protocol is to be used with
256
patients, the normalization procedures need to be addressed further.
257
Even though the choice of MVC in this study is based on existing recommendations, our
258
findings show different reliability values for absolute and normalized data. This
259
discrepancy was also found by Zakaria et al. (1996), who found that absolute data show
260
higher reliability compared with normalized data. The reason for these differences is
261
unknown, but might be influenced by variability in performing the MVC and the challenges
262
arising when comparing one test position with another (Zakaria et al., 1996). Furthermore,
263
the literature indicates that even though normalization is performed to reduce variability,
264
the magnitude of variance can be increased during normalization (Jackson et al., 2009 ;
265
Nordander et al., 2004).
266 267
4.2. Reliability of a hand-held dynamometer and surface electromyography
268
In this study conducted on healthy subjects, LOA shows acceptable reliability for the hand-
269
held dynamometer. However, LOA shows questionable reliability when using EMG. The
12
270
ICC shows acceptable reliability for both hand-held dynamometer and EMG. The mean
271
differences in EMG amplitude tended to increase at higher levels of the scale in some
272
cases (Figures 4 and 5), pointing at larger standard error of measurement for healthy
273
subjects with higher compared with lower EMG amplitude. Relative reliability describes the
274
degree at which subjects maintain their position in a sample with repeated measurements,
275
whereas absolute reliability is the degree at which repeated measurements vary for
276
subjects (Atkinson and Nevill, 1998). Therefore, relative reliability is affected by the ratio of
277
the variability between subjects and the total variability (Rankin and Stokes, 1998), which
278
means that heterogeneous subjects are more likely to produce a higher ICC value than
279
homogeneous subjects (Weir, 2005; de Vet et al., 2006). Absolute reliability is not affected
280
by the total variability as it is related to the difference between each subject. Our results
281
underlined the importance of reporting both absolute and relative reliability in line with
282
GRASS guidelines (Kottner, 2011).
283
Magnusson et al. (1990) indicate that a variation of 11% is to be expected when
284
measuring force signals. Therefore, the EMG variation may be altered if the 11% of
285
variation is associated with normal biological variance and not related to measurement
286
error (Magnusson et al., 1990). Despite the relatively inconsistent results concerning the
287
EMG relative and absolute reliability, the literature also shows different reliability results for
288
m. trapezius superior measured with EMG. Almosnino et al. (2009) found lower reliability
289
of isometric flexion of m. trapezius superior with ICC=0.64 and 95% confidence interval of
290
0.11-0.85. However, contrary to our study focusing on RMS values, Almosnino et al.
291
(2009) investigated EMG onset values. Nordander et al. investigated the variability of m.
292
trapezius superior in different work tasks and found low between-day variability with a
293
coefficient of variation of 8% (Nordander et al., 2004).
13
294
Since the hand-held dynamometer shows high reliability, it is relevant to include this
295
outcome measurement in future studies evaluating the functional status of the shoulder
296
among athletes or patients.
297
4.3. Clinical implications
298
In this study isometric contractions at submaximal level were investigated as these are
299
more suitable for patients compared with existing test positions (Magnusson et al., 1990;
300
Hayes et al., 2002; Forthomme et al., 2011). Patients with rotator cuff rupture often have a
301
decreased ability to stabilise the humeral head in cavitas glenoidale especially during
302
movement due to muscular loss (Ainsworth, 2006; Smith and Smith 2010; Jenp et al,
303
1996). Further, patients with rotator cuff rupture are at risk of proximal sub-luxation caused
304
by decreased ability to maintain the humeral head in the cavitas glenoidale (Ainsworth,
305
2006). This can worsen their symptoms since the subacromial space can be decreased. In
306
the literature many of the tests consisting of internal and external rotation include arm
307
abduction or flexion also resulting in decreases of the subacromial space during rotation.
308
Especially the combination of arm abduction and internal rotation is often used to provoke
309
pain in relation to shoulder impingement (Magee, 2007). Thus the test positions for internal
310
and external rotation with 0° of arm abduction or flexion used in this study may be more
311
appropriate in patients with rotator cuff tears. Furthermore, all the tests with submaximal
312
contraction were performed isometrically using a non-elastic band. In this way the subjects
313
could control the amount and rate of force development, which may also be useful with
314
patients since rapid movement may compromise the stability of the humeral head even
315
more.
316
The 45o abduction test was also performed as we hypothesized that a diminution of the
317
subacromial space. The flexion tests were performed at both 45° and 90°. Presumably, not
14
318
all patients would be able to perform 90o of flexion so it could be considered to record a
319
45° flexion only.
320
Even though the isometric contractions may be the most appropriate in patients, a
321
dynamic movement was also included in this study with the purpose of measuring the
322
interaction between m. trapezius superior and deltoideus anterior during a dynamic
323
movement. The dynamic arm movement showed acceptable relative reliability. We thus
324
suggest that the dynamic arm movement test can be used in patients since the movement
325
is performed without external load and at a low pace.
326 327
4.4 Methodological considerations
328
The measurement of force with a hand-held dynamometer reflects the sum of active
329
muscles, while the use of RMS EMG provides the researcher with recordings of muscle
330
activity from specific muscles. The present study is methodologically sound as we used a
331
randomization process in a balanced order as well as a high degree of standardization
332
concerning the performed isometric contractions. Further, blinding of subjects and
333
examiners from results of the isometric contractions was used to ensure that the examiner
334
did not influence the subjects’ performance. On the other hand, crosstalk, skin movement
335
and movement artefacts are always an issue when measuring with EMG. Even though
336
many initiatives have been made to improve existing protocols, the current study also has
337
some limitations. First, recordings from men and women were pooled even though sex
338
differences are reported in muscle coordination (Côté, 2012). There was no warm-up
339
period prior to MVCs but the participants performed a single MVC trial to become
340
familiarized with the procedure. This first MVC trial was disregarded from the analysis.
341
Moreover, the use of MVC in relation to the EMG normalization procedure may not be
15
342
appropriate in patient populations. Future studies are needed to investigate reliability in
343
patient populations.
344 345
5. Conclusions
346
The hand-held dynamometer showed high absolute and relative reliability during isometric
347
flexion, abduction, and internal and external rotation among healthy subjects. Further, the
348
EMG showed acceptable relative reliability when measuring muscle activity from m.
349
trapezius superior and deltoideus anterior in isometric submaximal flexion, abduction and
350
a dynamic arm movement. Therefore, the outcome measurements have the potential to
351
detect changes in muscle strength and muscle activity. The current protocol may be used
352
in patient populations but the use of normalization with respect to MVC can be
353
problematic.
354 355
Acknowledgements
356
This study was partly supported by a grant from Gigtforeningen (The Danish Rheumatism
357
Association).
358 359
Conflict of interests
360
There is no conflict of interests from any of the authors.
361
16
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20
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21
Table 1: Description and reliability results from studies using strength measured with a handheld dynamometer as outcome measure. Study
Test positions o
Magnusson
90 abduction with manual resistance.
et al. 1990.
Shoulder
Movement
n
Reliability
Non-dominant. The
Isometric
9
r = 0.94-0.98
Isometric
8-
ICC = 0.96¹, 0.92²
dominant shoulder was tested with an isokinetic machine. o
Hayes et al. Elevation with 90 flexion in the plane of scapula (30 2002.
o
Symptomatic shoulder
frontal).
9* o
External rotation in supine position with 90 arm
ICC = 0.92¹, 0.82²
abduction. Internal rotation in supine position with 90o arm
ICC = 0.85¹´²
abduction. Lift-off from lumbal spine.
ICC = 0.70¹, 0.79²
Celik et al. Test of specific muscles, among these
Dominant and non-
2012.
dominant
- m. trapezius superior during elevation of the shoulder
Isometric
o
- m. deltoideus anterior during 90 flexion of the arm Cadogan
et
o
Abduction 10 in the plane of scapula.
al. 2011.
Symptomatic and asymptomatic shoulder
External rotation during sitting.
Isometric
35 +
ICC = 0.45-0.97
22*
ICC = 0.72-0.95
40*
ICC = 0.91-0.98¹, 0.77-0.84² LOA = 2.2-7¹, 6.3-8.5²
ICC = 0.91-0.99¹, 0.68-0.74² LOA = 1.1-3.2¹, 3.2-4.4²
22
Cools et al. Test of internal and external rotation in different 2014.
Not mentioned
Isometric
30
shoulder and patient positions. Internal rotation in sitting position with 0 o abduction.
ICC = 0.96-0.99¹, 0.98²
MDC= 14.07-22.11¹, 7.76² External rotation in sitting position with 0 o abduction.
ICC = 0.96-0.97¹, 0.96² MDC = 11.52-12.80¹, 6.00²
Abbreviations: * refer to subjects with shoulder pain, ¹ refer to intra-rater reliability and ² refer to inter-rater reliability.
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Table 2. The relative and absolute reliability of the m. trapezius superior (TS) and m. deltoideus anterior (DA) root mean square during maximum voluntary contraction and of the hand-held dynamometer during isometric contractions. ICC (95% CI)
LOA (95% CI)
LOA %
Maximum voluntary contraction
TS
0.86 (0.70-0.94)
0.36 (-0.30-0.43)
67.1%
DA
0.79 (0.48-0.91)
0.86 (-1.13-0.58)
39.4%
Flexion 45o
0.91 (0.81-0.96)
0.14 (-0.13-0.15)
7.6%
Flexion 90o
0.91 (0.79-0.96)
0.14 (-0.13-0.14)
7.3%
Abduction
0.94 (0.85-0.98)
0.10 (-0.07-0.12)
4.5%
Internal rotation
0.98 (0.95-0.99)
0.07 (-0.07-0.07)
3.2%
External rotation
0.89 (0.76-0.95)
0.12 (-0.12-0.13)
6.4%
Isometric contractions
Abbreviations: ICC: Intraclass correlation coefficient, LOA: Limits of agreement, CI: confidence interval.
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Table 3. The relative and absolute reliability of the absolute and normalized surface electromyography (EMG) root mean square recorded from the m. trapezius superior (TS) and m. deltoideus anterior (DA) during isometric and dynamic contractions. ICC Absolute EMG
ICC Normalized EMG
LOA Absolute EMG
LOA Normalized EMG
LOA %
LOA %
(95% CI)
(95% CI)
(95% CI)
(95% CI)
Absolute EMG
Normalized EMG
Flexion 45o TS
0.88 (0.71-0.95)
0.72 (0.46-0.87)
0.25 (-0.19-0.31)
40.31 (-37.82-42.79)
59.1%
48.2%
Flexion 45o DA
0.88 (0.73-0.94)
0.57 (0.22-0.79)
0.70 (-0.68-0.72)
69.28 (-52.35-86.22)
26.0%
52.5%
Flexion 90o TS
0.82 (0.63-0.92)
0.60 (0.27-0.80)
0.33 (-0.34-0.32)
67.33 (-80.53-54.13)
68.4%
66.5%
Flexion 90o DA
0.92 (0.83-0.96)
0.59 (0.26-0.80)
0.55 (-0.60-0.49)
70.34 (-56.44-84.25)
20.0%
52.2%
Abduction TS
0.90 (0.79-0.96)
0.72 (0.46-0.87)
0.30 (-0.27-0.33)
49.48 (-55.98-42.98)
52.8%
42.4%
Abduction DA
0.89 (0.76-0.95)
0.63 (0.31-0.82)
0.67 (-0.72-0.61)
70.79 (-55.42-86.16)
22.7%
49.0%
Isometric contractions
Dynamic contractions
Dynamic TS
0.99 (0.97-0.99)
0.96 (0.91-0.98)
0.12 (-0.10-0.14)
19.91 (-21.61-18.21)
65.6%
55.9%
Dynamic DA
0.86 (0.71-0.94)
0.89 (0.86-0.97)
0.63 (-0.50-0.77)
32.79 (-20.72-44.86)
42.0%
50.4%
Abbreviations: ICC: Intraclass correlation coefficient, CI: confidence interval, LOA: Limits of agreement
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Fig. 1. A. Design of the test procedure. The procedure was repeated with 1-3 days in between. MVC = maximum voluntary isometric contraction. TS: m. trapezius superior, DA: m. deltoideus anterior. Four isometric contractions were performed in flexion, abduction, and with internal and external rotation. See Methods section for further details. B. Electrode placement for m. trapezius superior and m. deltoideus anterior. Fig. 2. Performance of maximum voluntary isometric contraction (MVC) and isometric submaximal contractions. A: MVC performed for m. trapezius superior and m. deltoideus anterior. B: Dynamic arm flexion. C: Isometric submaximal contractions. a=flexion at 45°, b=flexion at 90°, c=abduction at 45°, d=internal rotation, e=external rotation. Fig. 3. Bland-Altman plots for test-retest reliability of the absolute root mean square values recorded from m. trapezius superior and m. deltoideus anterior during maximum voluntary isometric contraction and of the hand-held dynamometer isometric contractions. Fig. 4. Bland-Altman plots for test-retest reliability of the absolute and normalized root mean square values recorded from m. trapezius superior during isometric and dynamic contractions. Fig. 5. Bland-Altman plots for test-retest reliability of the absolute and normalized root mean square values recorded from m. deltoideus anterior during isometric and dynamic contractions.
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Figure
Figure 1
4 x isometric maximum contractions 5 sec.
Submaximal dynamic and isometric contractions
Dynamic arm flexion 2 sec. upward & 2 sec. downward
2 min rest
Maximum voluntary contraction
2 min rest
A
Isometric contractions
5 sec. 30 sec. rest in between repetition 2 min. rest between each direction
30 sec. rest in between repetition 2 min. rest between TS and DA MVC
Procedure repeated after 1-3 days
B
Electrode placement for m. trapezius superior
Electrode placement for m. deltoideus anterior
Figure 2
A: Maximum voluntary contraction for respectively m. trapezius and m. deltoideus anterior
B: Dynamic arm flexion
C: Isometric test contractions. a : 45o arm flexion, b : 90o arm flexion, c :45o arm abduction, d : internal arm rotation, and e: external arm rotation
Figure 3 Maximum voluntary contraction
Isometric contractions – Hand-held dynamometer Flexion 45o
Flexion 90o
Difference between test and retest
Difference between test and retest
m. trapezius superior
Difference between test and retest
Abduction
Internal rotation
Exernal rotation
Difference between test and retest
Difference between test and retest
m. deltoideus anterior
Mean of test and retest
Mean of test and retest
Mean of test and retest
Figure 4 Isometric contractions Flexion 90o
Abduction
Difference between test and retest
Flexion 45o
Dynamic contraction
Difference between test and retest
Absolute root mean square values from m. trapezius superior
Mean of test and retest
Mean of test and retest
Mean of test and retest
Normalized root mean square values from m. trapezius superior
Mean of test and retest
Figure 5 Isometric contractions Flexion 90o
Abduction
Difference between test and retest
Flexion 45o
Dynamic contraction
Difference between test and retest
Absolute root mean square values from m. deltoideus anterior
Mean of test and retest
Mean of test and retest
Mean of test and retest
Normalized root mean square values from m. deltoideus anterior
Mean of test and retest
Kathrine S Andersen received her degree as a physiotherapist in 2011 from University College Nordjylland and her Master of Science in Clinical Science and Technology from Aalborg University in 2013. She is currently employed at Viborg Region Hospital as a physiotherapist with responsibility for development and research of clinical practice in the field of neurology. Furthermore she is employed as a research physiotherapist at Aalborg University Hospital, where her research field is patients with shoulder pain and altered kinematics.
Birgitte H Christensen received her degree as a physiotherapist in 2011 from University College Nordjylland and her Master of Science in Clinical Science and Technology from Aalborg University in 2013. She is currently employed at Aalborg University Hospital as a physiotherapist with responsibility for development and research of clinical practice in the field of neurology, pediatrics and neurosurgery. Furthermore she is employed as a research physiotherapist at Aalborg University Hospital, where her research field is patients with shoulder pain and altered kinematics.
Afshin Samani received his PhD in Biomedical Engineering and Science in 2010 from Aalborg University, Denmark. He is currently employed as an assistant professor in sports science and ergonomics at the Department of Health Science and Technology at Aalborg University, Denmark. He is co-director of the laboratory for Ergonomics and Work-related Disorders. His specific research field is focused on methods of quantification of work exposure, risk factors for the development of musculoskeletal disorders and interactions between muscle pain and motor control among computer users. Pascal Madeleine was born in Toulouse, France, in 1969. He received his Dr. Scient. degree and PhD from Aalborg University, Denmark. He is currently employed as a Professor at the Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology at Aalborg University, Denmark. He is head of the research interest group within Physical Activity and Human Performance and co-director of the laboratory for Ergonomics and Work-related Disorders. He has published more 130 peer reviewed scientific journal publications and book chapters. His main area of research interests are the development and application of novel methods and technologies in Ergonomics and Sports.
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Kathrine S Andersen
Birgitte H Christensen
Afshin Samani
Pascal Madeleine
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