Download EMG of arm and forearm muscle activities with regard

Acta of Bioengineering and Biomechanics
Vol. 4, No. 2, 2002
EMG of arm and forearm muscle activities
with regard to handgrip force in relation
to upper limb location
DANUTA ROMAN-LIU, TOMASZ TOKARSKI
Central Institute for Labour Protection, ul. Czerniakowska 16, 00-701 Warszawa, Poland.
E-mail: [email protected]
The aim of the study was to assess the maximum force of the handgrip depending on four different
upper limb locations and to analyse the influence of limb location on muscle activities connected with the
handgrip force. Five upper limb and shoulder muscles were examined: extensor carpi radialis longus,
flexor carpi ulnaris, biceps brachii caput breve, deltoideus pars anterior and trapezius pars descendent.
The results showed that the four upper limb locations chosen are differentiated by the value of maximum
handgrip force. The study also confirmed the hypothesis that upper limb location influences the
component of muscle activity which is responsible for handgrip force exertion. Such a phenomenon was
especially obvious in extensor carpi radialis and deltoid pars anterior muscles. The activity of the flexor
carpi ulnaris and biceps brachii caput breve muscles although strongly connected with handgrip force
exertion was not sensitive to upper limb location.
Key words: electromyography, handgrip force, upper limb location, muscle activity
1. Introduction
In literature on the different types of upper limb activities, the broadest area is
devoted to research performed on the transverse grip commonly known as handgrip.
This situation can be due to the fact that handgrip is most commonly connected with
work tasks. In work settings, the handgrip is perceived as one of the most important
hand functions used while gripping an object in conjunction with twisting, rotating,
lifting, lowering, pressing down, pushing or pulling.
The first studies aimed at the measurement of maximum handgrip force did not
consider upper limb location [12], [21], [30], [39]. However, in 1981, The American
Society of Hand Therapists recommended the so-called standard upper limb location
as appropriate for the measurement of maximum handgrip force [28]. Standard upper
limb location was defined as seated with shoulder adducted and neutrally rotated,
elbow flexed at 90°, forearm and wrist in neutral position.
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D. ROMAN-LIU, T. TOKARSKI
Although there have been quite a few research works showing the values of
maximum handgrip for the standard upper limb location [2], [4], [5], [8], [14], [15],
[19], [31], [42], research work for standard, as well as other strictly determined upper
limb locations, has also been performed [11], [20], [23]–[26], [37]. Those studies have
proved that the wrist angle, arm flexion, pronation and supination influence the value
of maximum handgrip force.
For the evaluation of muscle activities associated with force exertion the surface
electromyography method is well established. The amplitude of the EMG signal
quantitatively expresses muscle activity [16], [18], [32], [40] and has been used in
studies of various vocations to estimate muscle loads in tasks involving upper limbs [9],
[17], [38].
As maximum force exerted by the hand depends on upper limb location, for
musculoskeletal load assessment it is important to determine how the value of
maximum force changes in relation to upper limb location. Although studies which
considered this problem (as cited above) have been performed, taking into account
variety of upper limb locations, further research is still needed for normalisation
purposes.
The force which the muscle exerts as well as muscle tension expressed by the
amplitude of the EMG signal depend on muscle length (upper limb location) [3]. Also
the study of DUQUE, MASSET and MALCHAIRE [7] confirmed that differences in EMG
signal amplitude in the flexor carpi radialis muscle should occur according to wrist
flexion and extension, and the study of Wright (as cited in [6]) showed that the activity
of the long head of the biceps brachii depends on the arm abduction and arm rotation.
Muscle activity during force exertion can be spread up between muscle activity for
upper limb stabilisation in a defined upper limb location and activity connected with
the external force exertion. It should be expected that not only the component of
muscle activity, which is responsible for upper limb stabilisation, depends on upper
limb location but muscle activity associated with force exertion is influenced by upper
limb location as well. Therefore, it is also an interesting problem to see whether the
component of muscle activity, which is associated with handgrip force exertion, varies
according to upper limb location.
Studies considering this problem in relation to shoulder muscles were performed
by SPORRONG, PALMERUD and HERBERTS [35], [36]. The upper limb location tested
were flexion and abduction of arm. The studies have revealed that although there is no
influence of handgrip activity on the trapezius muscle there is such on the middle part
of the deltoid muscle, supraspinatus and infraspinatus. However, those studies do not
consider forearm muscles.
The aim of the present study was to assess the maximum force of the handgrip in
relation to four different upper limb locations and to analyse the influence of the limb
location on shoulder, arm and forearm muscle activities associated with handgrip
force.
Arm and forearm EMG of muscle activity
35
A hypothesis has been put forwarded that the muscle involvement could vary
according to upper limb location as exertion of the same handgrip force can require
different muscle activities according to upper limb location.
2. Methodology
2.1. Participants
There were nine young, right hand dominant men aged from 20 to 24 years
(average 21.89 years) recruited from a group of male students of the Academy of
Physical Education. The participants were healthy, had no history of muscle pain and
were characterised by similar anthropometric dimensions. Their average body mass was
88 kg (from 80 to 93) and body height 179 cm (from 177 to 182).
The study was carried out with the approval of the Academy of Physical
Education Ethics Committee. Before the experiments, an informed consent was
obtained.
2.2. Experimental design
Experimental procedure. During the experiments the handgrip force and EMG
signal from five muscles were measured. The experiment was divided into two tests.
During Test 1, maximum handgrip force (Fmax) and respective EMG signals from
selected muscles for four upper limb locations were measured and recorded.
During Test 2 for the same four upper limb locations the EMG signal from five
muscles was measured when force was exerted on the level of 10% Fmax.
The participants were asked to build up the force gradually without jerking and to
hold the exertion for 3 seconds. During exertion of force, the participants were in
a sitting position with their back straight and left limb relaxed. The sequence of
variants of upper limb location was randomised for each participant.
Muscle strength capabilities were measured by hand dynamometer against which
the participants exerted contractions of muscles in static (isometric) tests. The
dynamometer was fastened onto the metal support in a position which allowed
exerting handgrip force in a defined upper limb position. During the test the
participants controlled the force level with the aid of a digital meter.
Upper limb location. The four upper limb locations under examination were
marked location A, location B, location C and location D. Illustration of the limb
locations is presented in figure 1.
Location A was the standard upper limb location as defined above. In locations B
and C, there was no abduction in arm, however, the arm was flexed of 45°. The angle
between arm and forearm was set to 135° and there was supination of forearm at 30°.
The wrist was in neutral position. The difference between locations B and C is in
D. ROMAN-LIU, T. TOKARSKI
36
rotation of the arm around the axis. In location B there is no rotation as in location C
there is rotation of 45°. In location D the shoulder was flexed at 90° with full
extension in the elbow.
Location B
Location A
Location C
Location D
Fig. 1. Upper limb locations under examination
Specific locations were chosen as they were significantly different from each other
and it was comparably easy to make measurements and repeat the upper limb locations
in the sequential experiments.
Muscle activity. To examine muscle activity, surface electromyography (EMG) was
applied. In experiments, the EMG signals from five main muscles of shoulder girdle, arm
and forearm were registered. The anatomical localisation of the muscles was done by
feel as the participant put them to isometric tension. Electrodes were attached along the
direction of the muscle fibres in the bulky central part of the muscle.
Arm and forearm EMG of muscle activity
37
The examined muscles were: two muscles of the forearm – extensor carpi radialis
longus and flexor carpi ulnaris, two muscles of the arm – deltoid anterior and biceps
brachii caput breve and one muscle of the shoulder girdle – trapezius pars
descendents. Those muscles were selected because they play a different role [1], [6],
[9], [22], [29], [41] and different involvement of the analysed muscles in the
performed task was expected.
EMG measurements. EMG measurements were performed during isometric muscle
contractions. The Muscle Tester MESPEC 4000 (Mega Electronics, Finland) and an IBM
computer were used to measure and store data. The EMG signal was recorded by means
of MS-OOS (Medicates, Denmark) surface electrodes. To ensure consistent electrode
placement for each of the test sessions, the participant’s skin was marked around the
electrodes. The skin was properly prepared to obtain skin resistance below 2 kΩ.
Preamplifiers mounted close to the electrodes allowed recording of the non-artefacted
signal. The EMG signal was sampled using a 12 bit A/D converter of a sampling rate of
1000 Hz.
Force measurements. Measurements of the grip strength were performed using
equipment which consisted of a DR-3 hand dynamometer with a grip span connected
through a WT8-RS eight-channel amplifier with a 12-bit analogue-digital converter to
the PC class computer. The equipment was produced by JBA (Poland). The nominal
measuring range of the hand dynamometer was 1200 N with maximal linear error lower
than 5%. An auxiliary, specially developed CPS_v_2.0 software allowed recording and
graphical representation of the actual value of strength from the dynamometer and after
the end of the test made it possible to show the measured value.
2.3. Data analysis
An analysis was performed of the differences in maximum handgrip force recorded
in Test 1 and differences in EMG signal according to upper limb location.
The analysis of the EMG signal was based on software supplied with the MESPEC
4000 equipment, which was used for measuring and recording the EMG signal. For
the analysis, integrated amplitude of the EMG signal, which converts information
about muscular tension for a given muscle, was employed. The EMG signals were full
wave rectified and averaged within windows that were 0.5 s in length (IEMG).
For each of the muscles and each of the four upper limb locations under examination
calculations were made of the ratio of IEMG measured during Test 2 related to IEMG
measured in Test 1 for the same upper limb location. In this way, differences in the EMG
signal which could have occurred due to muscle activity connected with upper limb
mass, shift with the skin which change electrode location with respect to the muscle, and
the necessity of limb stabilisation with regard to various upper limb locations were
excluded. It means that the IEMG ratio was a measure of muscle activity on the level of
10% of maximum handgrip force. Differences in the stabilisation of upper limb
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D. ROMAN-LIU, T. TOKARSKI
according to various upper limb locations were eliminated. At this stage differences in
the IEMG ratio, which can occur, are caused only by the influence of upper limb
location on the activity of the muscle associated with handgrip force exertion.
The IEMG ratio on the level close to 1.00 means that activation of the muscle while
exerting maximum handgrip force and while exerting 10% Fmax are similar. This can
suggest that the muscle in the upper limb location being analysed is not involved in the
handgrip. On the other hand, when the IEMG ratio is close to 0.10 it can suggest that the
muscle is strongly involved in force exertion. The higher the IEMG ratio above 0.10 is,
the weaker the involvement of the muscle in handgrip force exertion.
For statistical analysis, software Statistica (from StatSoft) was used. The analysis
of differences between maximum handgrip force value according to upper limb
location as well as between IEMG ratio in the four upper limb locations was
conducted by the variance analysis ANOVA. To establish differences between specific
groups of variants a post-hoc analysis was made.
3. Results
Handgrip force [N]
Mean values and standard deviation of maximum handgrip force are presented in
figure 2. The value of exerted force is between 604 N and 635 N. The highest
maximum handgrip force is in location B, the lowest – in location D.
upper limb location
Arm and forearm EMG of muscle activity
39
Fig. 2. Mean value, standard deviation and standard error of maximum handgrip force
in four upper limb locations
Statistic F of the variance analysis ANOVA was equal to 4.260 with the
probability level of 0.006. Table 1 presents values of the probability level of a posthoc analysis showing the significance level of differences in maximum handgrip force
values between the upper limb locations under examination.
Table 1. The value of the probability level in a post-hoc analysis (test NIR)
performed to differentiate between maximum handgrip forces
for particular upper limb locations (statistically significant differences are marked in bold)
Location
Location A–B
Location A–C
Location A–D
Location B–C
Location B–D
Location C–D
p
0.051
0.345
0.059
0.009
0.001
0.278
In most cases, differences in the maximum handgrip force in the analysed upper
limb locations are statistically not significant. Only the differences between locations
marked B and C as well as B and D are statistically significant. However, in the
differentiation of locations A and B the value of the probability level is not much
higher than 0.05, which means that differences in maximum handgrip force between
locations A and B can be assumed. When differentiating between location A and
location D similar situation occurs.
The mean values and standard deviation of IEMG ratio recorded for five muscles
being examined are presented in figures 3 through 7.
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D. ROMAN-LIU, T. TOKARSKI
Fig. 3. Mean value, standard deviation and standard error of the IEMG ratio
of the trapezius descendent muscle in four upper limb locations
The values of the IEMG ratio vary for particular upper limb locations and for the
different muscles examined. The highest values are for the trapezius muscle (figure 3).
For upper limb locations marked A and C the mean value of the ratio is close to 1. For
upper limb locations B and D the mean values are close to 0.8.
Arm and forearm EMG of muscle activity
Fig. 4. Mean value, standard deviation and standard error of the IEMG ratio
of the muscle deltoid anterior in four upper limb locations
Fig. 5. Mean value, standard deviation and standard error of the IEMG ratio
of the biceps brachii caput breve muscle in four upper limb locations
Fig. 6. Mean value, standard deviation and standard error of the IEMG ratio
of the extensor carpi radialis muscle in four upper limb locations
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D. ROMAN-LIU, T. TOKARSKI
Fig. 7. Mean value, standard deviation and standard error of the IEMG ratio
of the flexor carpi ulnaris muscle in four upper limb locations
As far as the deltoid muscle is concerned (figure 4), the value of the IEMG ratio is
much lower for the upper limb location marked A (standard limb location) than for
other limb locations considered in the study. The highest value is for the location
marked B (close to 0.8).
Values of the IEMG ratio for the biceps brachii muscle differ, depending on the
upper limb locations, in the narrow range from 0.12 up to 0.13 (figure 5).
Also, for the extensor carpi radialis muscle differences in the IEMG ratio for
particular upper limb locations were not big (figure 6). The lowest value occurs for the
upper limb location marked B (0.14) and the highest for location C (0.17).
In the case of the flexor carpi ulnaris muscle, the values are very similar (close to
0.11) and differences in the IEMG ratio for particular upper limb locations can be
neglected.
The differences in the IEMG ratio of the muscles examined according to upper
limb location were analysed by the variance analysis ANOVA. Statistics and the
probability level for particular muscles are presented in table 2.
Table 2. Values of F statistics and the probability level in variance analysis performed
to differentiate between muscle activities (IEMG ratio) in trapezius pars descendents, deltoid anterior,
biceps brachii caput breve, extensor carpi radialis and flexor carpi ulnaris
for particular upper limb locations (statistically significant differences are marked in bold)
Arm and forearm EMG of muscle activity
Muscle
Trapezius pars descendents
Deltoid anterior
Biceps brachii caput breve
Extensor carpi radialis
Flexor carpi ulnaris
F
1.485
58.936
0.441
21.033
0.382
43
p
0.221
0.001
0.724
0.014
0.766
Table 2 shows that differences in the IEMG ratio according to upper limb location
reached statistical significance only for deltoid anterior and extensor carpi radialis
muscles. For those two muscles a post-hoc analysis was performed (table 3).
Table 3. The value of the probability level in a post-hoc analysis (test NIR) performed to differentiate
between muscle activities (IEMG ratio) in deltoid anterior and extensor carpi radialis for particular upper
limb locations (statistically significant differences are marked in bold)
Location
Location A–B
Location A–C
Location A–D
Location B–C
Location B–D
Location C–D
p
Deltoid anterior
0.001
0.001
0.001
0.001
0.001
0.602
Extensor carpi radialis
0.039
0.146
0.245
0.001
0.338
0.093
For the deltoid anterior muscle the IEMG ratio is statistically differentiated in all
but one case. Only differences between upper limb locations C and D are statistically
not significant. For the extensor carpi radialis muscle the statistically significant
differences are between locations A and B, as well as B and C.
4. Discussion
The values of maximum handgrip force for the standard upper limb location
obtained in our study are higher than those of other studies [2], [4], [5], [11], [14],
[15], [19], [20], [37]. Only CROSBY et al. [5] arrived at values of the maximum
handgrip force that were similar to ours. For the three other limb locations examined
here, no other references have been found in the literature. Most studies performed on
a broad area of upper limb locations [11], [15] [20], [26] have shown the values of
maximum handgrip force to be lower than those derived from the upper limb location
examined in this study. This may be not only because the upper limb locations
examined here allow for higher maximum handgrip force exertion but also because the
group under examination consisted of young males with sports background.
Studies presented by KATTEL et al. [20], SU et al. [37], MARLEY and WEHERMAN
[25], KUZALA and VARGO [23] have revealed that the maximum handgrip force for
standard upper limb location is not the highest one when compared with other limb
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D. ROMAN-LIU, T. TOKARSKI
locations. A similar situation occurred in the study presented. The highest value of
handgrip force was for the upper limb location marked B and the lowest for the
location marked D. In most cases, the differences in the maximum handgrip force in
respective upper limb locations were statistically not significant. It should also be
noted that differences in the mean value of forces were not very big, which suggests
that upper limb locations selected in the study do not greatly differentiate in respect of
maximum handgrip force, although a variance analysis (F = 4.260, p = 0.006)
confirms the hypothesis that upper limb location influences the maximum handgrip
force.
The activities connected with handgrip force generation influence the EMG of
upper limb muscles. A study by OHTSUKI [29] has shown the correlation between
handgrip force and the integrated amplitude of the EMG signal for finger flexor
muscles. In the present study, for the flexor carpi ulnaris muscle the mean values of
the IEMG ratio for the four upper limb locations examined were on a very similar
level (about 0.11). It means that the main role of this muscle is strongly involved in
handgrip force exertion. There are no statistically significant differences between
the upper limb locations under examination, which means that changes in upper
limb location, defined by arm flexion and rotation and forearm flexion and rotation,
have no influence on the activity of this muscle during maximum handgrip force
exertion.
Mean values of the IEMG ratio for the extensor carpi radials muscle are in the range
from 0.14 to 0.17. This can suggest that most of the muscle activity is connected with
maximum handgrip force. There are statistically significant differences in muscle activity
between location B and location C, showing that rotation of the arm influences the
activity of the extensor carpi ulnaris muscle while exerting handgrip force.
The mean value of the IEMG ratio of the biceps brachi muscle in the upper limb
locations under examination is in the range from 0.12 to 0.13 and for this muscle there
are no statistically significant differences between limb locations. The study of
YAMAGUCHI et al. [41] has revealed that the long head of the biceps does not appear
to have an active role in shoulder stabilisation. The results of AOKI [1] have shown
that the activity of rapid wrist movements influence the biceps brachii muscle. Both of
those studies are in line with the results derived from the present study, which have
also revealed that limb location does not have any influence on biceps brachii muscle
activity while generating handgrip force. Such a result supports the thesis that the
biceps brachii muscle does not take part in the stabilisation of the upper limb.
It is generally accepted that the role of the trapezius muscle is to support posture. The
activity of the trapezius muscle has been shown to depend on the position of the arm
[10], [13], [27], [34]. A study by MATHIASSEN and WINKEL [27] has confirmed that the
amplitude of surface EMG recorded above the upper trapezius muscle depends on the
vertical and horizontal position of the arm. In the present study, the mean value of the
IEMG ratio for the trapezius descendent muscle is high. In two cases (location B and
location D) the mean value of the IEMG ratio is 0.78, while for the limb location A and
Arm and forearm EMG of muscle activity
45
location C the values are 0.92 and 0.89, respectively. Values higher than 1.00 suggest
that IEMG for 10% Fmax is higher than for maximum force, which is probable as this
muscle is sensitive to the precision with which the task is performed [33], and exerting
force on the level of 10% Fmax can be considered as such. There are no differences in the
IEMG ratio according to upper limb location. The results have shown that the trapezius
muscle is strongly involved in supporting the position of the upper limb and its
contribution in handgrip force exertion can be neglected.
For the deltoid anterior muscle the highest value of the IEMG ratio occurrs for
upper limb location B (mean value is equal to 0.82). For the other two limb locations
(C and D) the values are about one third lower. The lowest value is for location A –
mean value 0.19. Statistically significant differences in the values of the IEMG ratio
are between location A and the other upper limb locations. There are also differences
between B and C as well as between locations B and D. The results for the deltoid
muscle suggest that in upper limb location the deltoid muscle takes part in the force
exertion to a high degree, while in the other limb locations contribution in the
handgrip force of this muscle is much smaller. For the limb location marked B muscle
activity is due to the supporting upper limb location and contribution to force exertion
is very small. The main difference in limb location between A and the other locations
is the angle of arm flexion, which means that arm flexion has a considerable influence
on the deltoid anterior muscle activity. This statement has been supported by
KRONBERG, NEMETH and BROSTRÖM [22], who have found that the anterior and the
middle deltoid are the muscles responsible for arm flexion. A similar tendency in
anterior deltoid and middle deltoid muscles according to the flexion of the elbow has
been pointed out in the study of GIROUX and LAMONTAGNE [9]. The study of
DeDUCA and FORREST [6] has shown these muscles to be also involved in abduction
or adduction movements. Out study demonstrated differences in deltoid muscle
activation modulated by handgrip according to upper limb location by statistically
significant differences between location B and location D, location A and location C,
as well as location A and location B.
The results derived from this study can also be supported by the studies of
SPORRONG, PALMERUD and HERBERTS [35], [36], whose aim was to investigate the
influence of handgrip activity in different upper limb locations on trapezius muscle
activity and the middle part of the deltoid. No influence of handgrip activity on the
trapezius muscle was found. Much bigger changes were observed in the deltoid
muscle, in which there was a correlation between the degree of the muscle activity and
the intensity of the handgrip exertion in most of the arm positions tested.
5. Conclusions
The study has shown that maximum handgrip force is differentiated according to four
upper limb locations under examination. There has also been confirmed the hypothesis
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D. ROMAN-LIU, T. TOKARSKI
that upper limb location influences the component of muscle activity which is
responsible for handgrip force exertion. The upper limb location has been shown to
influence the EMG activity connected with the handgrip force exertion of the extensor
carpi radialis and deltoid anterior muscles. The activity of flexor carpi ulnaris muscle,
although the muscle is strongly connected with handgrip force exertion, is not sensitive
to upper limb location. A similar situation accrues for the biceps brachii caput breve
muscle, which plays a role in handgrip force exertion. However, the activity of this
muscle connected with handgrip force exertion is not influenced by upper limb location.
As regards those two muscles (flexor carpi ulnaris and biceps brachii caput breve) it can
be said here that the upper limb locations examined do not influence the activity
responsible for handgrip force exertion. For other upper limb locations the question is
still open.
Acknowledgement
This study is part of the National Strategic Programme “Occupational Safety and Health Protection
in the Working Environment”, supported in 1998–2001 by the State Committee for Scientific Research of
Poland. The Central Institute for Labour Protection is the Programme’s main co-ordinator.
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