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: daliu@ciop.pl 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.
34 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 (F max ) 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% F max. 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
36 D. ROMAN-LIU, T. TOKARSKI 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 A Location B 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
38 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% F max 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 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. Handgrip force [N] 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 p Location A B 0.051 Location A C 0.345 Location A D 0.059 Location B C 0.009 Location B D 0.001 Location C D 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.
40 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 41 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
42 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 43 Muscle F p Trapezius pars descendents 1.485 0.221 Deltoid anterior 58.936 0.001 Biceps brachii caput breve 0.441 0.724 Extensor carpi radialis 21.033 0.014 Flexor carpi ulnaris 0.382 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 p Deltoid anterior Extensor carpi radialis Location A B 0.001 0.039 Location A C 0.001 0.146 Location A D 0.001 0.245 Location B C 0.001 0.001 Location B D 0.001 0.338 Location C D 0.602 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
44 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% F max 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% F max 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
46 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. References [1] AOKI F., Activity patterns of upper arm muscles in relation to direction of rapid wrist movement in man, Experimental Brain Research, 1991, 83, 679 682. [2] BALOGUN J.A., AKOMOLAFE C.T., AMUSA L.O., Grip strength: Effects of testing posture and elbow position, Archives of Physical Medicine and Rehabilitation, 1991, 72, 280 283. [3] BIGLAND B., LIPPOLD O.C.T., The relationship between forces, velocity and integrated electrical activity in human muscles, Journal of Physiology, 1954, 123, 214 224. [4] CHATTERJEE S., CHOWDHURI B. J., Comparison of grip strength and isometric endurance between the right and left hands of men and their relationship with age and other physical parameters, Journal of Human Ergology, 1991, 20, 41 50. [5] CROSBY C.A., WEHBÉ M.A., MAWR B., Hand Strength: Normative Values, The Journal of Hand Surgery, 1994, 19A (4), 665 670. [6] DEDUCA C.J., FORREST W., Force analysis of individual muscles acting simultaneously on the shoulder joint during isometric abduction, Journal of Biomechanics, 1973, 6, 385 393. [7] DUQUE J., MASSET D., MALCHAIRE J., Evaluation of handgrip force from EMG measurements, Applied Ergonomics, 1995, 26 (1), 61 66. [8] FAIRFAX A.H., BALNAVE R., ADAMS R.D., Variability of grip strength during isometric contraction, Ergonomics, 1995, 38 (9), 1819 1830. [9] GIROUX B., LAMONTAGNE M., Net shoulder joint moment and muscular activity during light weight handling at different displacements and frequencies, Ergonomics, 1992, 35 (4), 385 403. [10] HAGBERG M., Electomyographic signs of shoulder muscular fatigue in two elevated arm positions, American Journal of Physical Medicine, 1981, 60, 111 121. [11] HALLBECK M.S., McMULLIN D.L., Maximal power grasp and three-jaw chuck pinch force as a function of wrist position, age, and glove type, International Journal of Industrial Ergonomics, 1993, 11, 195 206.
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