Electromyography analysis of the trapezius muscles in shoulder stiffness Visualization of specific muscle activity based on myogenic potential

Transcription

1 Electromyography analysis of the trapezius muscles in shoulder stiffness Visualization of specific muscle activity based on myogenic potential Saori YOSHINAGA, Eriko KURAMOTO, Hiroe KINOSHITA, Seiji NEMOTO Department of Fundamental Nursing, Faculty of Medicine, Miyazaki University, 5200, Kihara, Kiyotake, Miyazaki , Japan Interdisciplinary Graduate School of Medicine and Veterinary Medicine, Miyazaki University, 5200, Kihara, Kiyotake, Miyazaki , Japan Received on October 11, In final form on December 5, 2013 Abstract : Since shoulder stiffness is characterized by subjective symptoms centered mainly around the trapezius muscle, an objective evaluation may aid in understanding this condition. Thus, assessing the distribution and intensity of muscle activity may help to characterize shoulder stiffness. Using myogenic potential topography, the present study aimed to identify the changes in the state of the trapezius muscle among subjects with shoulder stiffness. Surface electromyogram recordings were obtained from the trapezius region of eight healthy women immediately before exercise, immediately after the end of exercise, and at the end of a 20 min convalescence period. Surface electromyogram data were analyzed by fast Fourier transform FFT, and power spectra were obtained. Based on the analyzed data, myogenic potential topography was composed at 6-bit resolution. Women who complained of shoulder stiffness showed remarkable changes in the lowfrequency domain of the surface electromyogram immediately after the end of exercise. Further, these changes were in accordance with the positions of the subjective symptoms reported by the subjects. Therefore, these events suggest a phenomenon specific to shoulder stiffness. Visually identifying the physiological alteration of muscle activity is possible using myogenic potential topography. Keywords : surface electromyogram, myogenic potential topography, shoulder stiffness, trapezius muscle Although shoulder stiffness is the most common subjective physical discomfort reported among Japanese individuals[1], the underlying mechanisms of the condition are not fully understood. In Western countries, this condition is often referred to as neck and/or shoulder pain[2-4]. Indeed, a number of studies have suggested that symptoms of neck pain, shoulder pain, or chronic nonspecific neck pain are similar to those of shoulder stiffness[5-6]. Since shoulder stiffness is defined based on various subjective symptoms of tension and pain centered mainly around the trapezius muscle[7-8], an objective evaluation may aid in understanding this condition. The trapezius muscle is of special interest to the pathogenesis of shoulder stiffness[9-10]. In occupational and laboratory settings, electromyogram EMG recordings have often been used to gain insight into the activity of the trapezius muscle. For instance, Itoh et al.[11] identified the electrical activities that correspond with the sensation of dull shoulder pain among patients with shoulder stiffness. Additionally, Leonard et al.[12] reported that the mean EMG activity of the upper trapezius muscle was significantly higher in subjects with neck pain than in those without. Results from these earlier studies indicate that shoulder stiffness may be evident in the characteristics of trapezius muscle activity. Thus, assessing the distribution and intensity of trapezius muscle activity may help to characterize shoulder stiffness. To our knowledge, no such assessment has been previously carried out. Topography can be used to produce a visual expression of a physiological phenomenon by plotting central values, such as brain potentials. Image processing can be used to quickly display the spatial distribution of huge potentials, and is the most useful method for evaluating the amplitude, or localization. Elucidating the myogenic potential topography of the human trapezius muscle may provide the foundation for visually assessing shoulder stiffness conditions. Therefore, in the present study, we defined myogenic potential topography as an adapting topography that classifies muscle activity according to the intensity of the electrical change generated in the trapezius muscle as a color, and expresses the relative state of muscle activity. Using myogenic potential topography, the present study sought to identify the changes in the state of the trapezius muscle accompanying the exercise loading among subjects with shoulder stiffness. We then used a projection of a myogenic potential topogram on a three dimensional body model to visualize the relationship with the actual complaints of the part centering on trapezius. Eight healthy women between 20 and 40 years of age with no known neurological or musculoskeletal disorders gave their informed consent to participate in this study. Each subject was questioned regarding the presence of shoulder stiffness currently experiencing shoulder stiffness, often experiences shoulder stiffness, or has never experienced shoulder stiffness, and were divided into those with shoulder stiffness or those without shoulder stiffness. Furthermore, the location of subjective symptoms in terms of stiffness, tension, pressure and pain, which the subject felt immediately before exercise and immediately after the end of exercise, and at the end of a 20-min rest convalescence, was assessed using a figure classified Vol.31 No

2 a b Fig.1 Possible positions of subjective symptoms a The presence of subjective symptoms was investigated at positions numbered 1-9. b The mimetic diagram positioned on the back of the model body. The location of subjective symptoms was investigated using the figure classified into the standard six domains : lateral neck regions 1 and 3, medial neck region 2, lateral to the superior scapulae 4 and 6, medial to the superior scapulae 5, lateral to the inferior scapulae 7 and 9, and medial to the superior scapulae 8. into the standard six domains, as illustrated in : lateral neck regions 1 and 3, medial neck region 2, lateral to the superior scapulae 4 and 6, medial to the superior scapulae 5, lateral to the inferior scapulae 7 and 9, and medial to the superior scapulae 8. Subjects were permitted to provide multiple answers regarding the location of their body complaint. This study was approved by the ethics review board of the Department of Medicine at Miyazaki University. Following a 10-min rest, subjective symptoms of neck and shoulder discomfort were assessed and 3 min of electromyogram EMG data were recorded from each subject while in a relaxed sitting posture. As described in, these measurements were repeated immediately after the end of exercise and at the end of convalescence. Isolated shoulder shrugs are likely the most specific exercise for the upper trapezius muscle, a conclusion that also is supported by EMG measurements[13-14]. Each subject performed one dynamic bilateral shoulder shrug every 3 to 4 s for 3 min with 2-kg dumbbells in each hand. The shoulder shrugs were performed an average of 46 times, and the number of repetitions did not differ significantly between subjects. Twenty adhesive electrodes Vitrode L-150 X, Nihon Kohden, arranged with an interelectrode distance of 35 mm, were used to record EMGs EEG-9100, Nihon Kohden. As illustrated in, the electrodes were concentrically arranged around the 7th cervical vertebrae in the upper and middle parts of the trapezius after fully removing sebum using alcohol swabs, and achieving a skin resistance of 50 kω or below. The reference electrodes were placed over the ear lobes, and EMG signals were collected monopolarly. Recording conditions included a time constant of 0.3 s and high-cut filters of 500 Hz. The hum filter was used if needed. Fig.3 Mimetic diagram illustrating the electrode arrangement Fig.2 Study protocol EMG data were analyzed by a fast Fourier transform FFT and power spectra were obtained. Using this data, myogenic potential topography was composed at 6-bit resolution. The EEG-9100 software QP-220A/ AK/, Nihon Kohden was used to create the topography. The maximum potential of the 8 Medical Imaging and Information Sciences

3 myogenic potential topogram was set at 30 μv 2, and was subdivided by frequency into five bands : 1-3, 1-5, 1-10, 10-15, and Hz. A three-dimensional female body model was made using a computer-character design tool POSER4, e- frontier, Inc. The myogenic potential topogram was mapped onto the model as a texture. According to the questionnaire, subjects A to E were classified as having shoulder stiffness while subjects F to H were classified as not having shoulder stiffness. Subject A to E experienced stiffness and tension centering on their neck and scapular region that were present prior to exercise and that continued until the end of convalescence. While subjects F to H reported not experiencing shoulder stiffness normally, they noted pain centering on the neck immediately after the end of exercise, which subsequently disappeared at the end of convalescence. Myogenic potential topography indicated a potential distribution in each of the frequency domains. After the end of exercise, subjects A to E showed a change of relatively high potential >30 μv 2 in the low-frequency 1-3 Hz domain of EMG, as illustrated in. Although the high potential distribution had disappeared by the end of convalescence, the potential that decreased to 10 μv 2 was still observed in subject E. Related to this, as illustrated in, the high-amplitude EMG waveform appeared immediately after the end of exercise. When the myogenic potential topogram was mapped onto the model, the high potential was distributed over the middle and upper parts of the trapezius, proximal to the neck and scapular regions. Myogenic potential topography was also a b c Fig.5 The electromyogram from subject C Electromyogram waveform of the electrodes 1, 2 that measured the change in potential following exercise. In comparison to preexercise a, the high-amplitude waveform appeared after exercise b, and also appeared intermittently at the end of convalescence c. Table 1 Characteristics of subjects Subjective symptoms position number before exercise after exercise convalescence A SS stiffness 1, 3 stiffness 1, 2, 3 tension 2 B SS none pain 3 pain 3 C SS tension 1, 3, 4, 6 tension 1, 3 tension 1, 3 D SS none pressure 3, 5 none E SS none pain 1, 3, 4, 6 pain 1, 3 F NSS none pain 1 none G NSS none pain 1, 2, 3 none H NSS none pain 3 none SS ; shoulder stiffness NSS ; no shoulder stiffness Fig.4 Myogenic potential topogram of subjects A-E After exercise, the change in high potential mainly appeared in the frequency band of 1-3 Hz, but disappeared at the end of convalescence. Vol.31 No

4 a b c d e Fig.6 Projection onto a three-dimensional female body model of myogenic potential topogram immediately after the end of exercise a Subject A ; A change in electrical activity was located near the right side of the scapular regions positions 3 and 6. b Subject B ; A change in electrical activity was located near the right side of the neck positions 2 and 3. c Subject C ; A change in electrical activity was located near the right side of the neck positions 2 and 3. d Subject D ; A change in electrical activity was located in the scapular regions positions 1, 4, 6, 7, 8 and 9. e Subject E ; A change in electrical activity was located near the scapular regions positions 1, 3, 5, and 6. compared to the subjective symptoms. In subject A, the change in electrical activity appeared at positions 3 and 6. In subject B, the change in electrical activity appeared at positions 2 and 3. In subject C, the change in electrical activity appeared at positions 2 and 3. In subject D, the change in electrical activity appeared at positions 1, 4, 6, 7, 8, and 9, while in subject E, the change in electrical activity appeared at positions 1, 3, 5, and 6. These findings confirmed that the distribution of myogenic potentials after exercise corresponded to the location of the subjective symptoms. On the other hand, no electrical change was observed in subjects F to H. In this research, muscle activity of the trapezius immediately before and after the end of exercise, and at the end of convalescence was observed, using myogenic potential topography as the technique to identify the region and the intensity of the muscle generating the activity by color. Frequency analysis by FFT was conducted on the myogenic potential measured by the arrangement of 20 electrodes, and power spectra were obtained. Although no specific frequency-analysis method was used, when examining the frequency components of specific muscle activity in subjects who complained of shoulder stiffness, the maximum frequency was reduced and the minimum Fig.7 Myogenic potential topogram of subjects F-H No remarkable change of potential was observed before and after exercise, and at the end of convalescence in the frequency band of 1-3 Hz. 10 Medical Imaging and Information Sciences

5 frequency was increased. Details in the five frequency bands were analyzed. Using this data, myogenic potential topography was composed at 6-bit resolution. The color change, which showed the change to a high potential region immediately after the end of exercise, was observed in the myogenic potential topogram of five subjects who complained of shoulder stiffness. Moreover, the EMG waveform of the electrode positions that recorded high potential exhibited high amplitudes compared to the same signals before exercise in these subjects. We attributed this color change to the increase in activity of the trapezius as a distribution of the potential. Conversely, this electrical change was not observed among the subjects who reported no shoulder stiffness. The sudden and involuntary painful muscle contraction of the skeletal muscle caused by movement is typically an exercise-induced muscle cramp. Ross et al.[15] reported seeing high-frequency and high-amplitude electrical discharge at the time of the maximum voluntary contraction in the motor unit action potential of the triceps surae muscle during cramping. On the other hand, Ohno et al.[16] reported that the EMG waveform in the hamstrings with an induced muscle cramp showed far less electrical discharge as compared with that during exercise. Although comparison with measurements during exercise was not completed in this research, since a clear difference was observed in the myogenic potential topogram and the EMG waveform by isotonic movement of the trapezius, it is possible that the trapezius of subjects who complained of shoulder stiffness underwent exercise-induced involuntary muscle contractions. Moreover, by projecting a myogenic potential topogram on the model, high-potential regions were distributed not throughout the entire trapezius but only in limited areas of the neck or scapular region, and the distribution changed with subjects. Furthermore, when the relevance of a myogenic potential topogram and actual complaint was examined, the distribution pattern of the myogenic potential and subjective symptoms were in agreement, and muscle activity in regions identified as exhibiting a subjective symptom was observed. Asano et al.[17] reported the existence of tonic muscular activity as a nociceptive response from an algesic substance in vitro. According to recent research, a high concentration of serotonin 5HT and glutamate in the interstitial fluid surrounding the trapezius muscle has also been reported in a subject with shoulder stiffness[18]. Although there are many factors that can induce involuntary muscle contractions, involuntary contractions induced in the trapezius in subjects that complain of shoulder stiffness may be a nociceptive response to exercise. Further, the subjects who complained of shoulder stiffness showed remarkable electrical change in the low-frequency domain 1-3 Hz of EMGs. The strength of a muscle contraction depends on the discharge frequency and mobilization of alpha motor neurons. Mobilization of a motor unit mainly takes the lead during a weak contraction, and the discharge frequency of alpha motor neurons greatly increases as the contraction intensifies. Moreover, frequency analysis indicates that an increase in contraction intensity reflects an increase in frequency[19]. Since the increase in potential immediately after the end of exercise in this research was remarkable in the 1-3 Hz lowfrequency bands, it was surmised to represent muscle activity related to weak muscle contraction. This could be a muscle activity phenomenon peculiar to the subjects who complained of shoulder stiffness because this electrical change was not observed among the subjects who reported no shoulder stiffness. Repeating this type of muscle contraction may change the hardness of the muscle and decrease blood flow to the muscle. It is very difficult to evaluate shoulder stiffness objectively when a clear underlying disease is not present. There is a paucity of reports on the spatial relationship between the state of the muscle that is presenting shoulder stiffness and subjective symptoms. It is impossible for a surface EMG to quantify the recruitment of motor units in electrical activity and the firing rate of each motor unit. However, since the EMG exhibits characteristics that reflect the activity of the muscle, it can acquire information about the total activity of each motor unit visually as a distribution or frequency by topogram myogenic potential. Since the presence of specific muscle activity was visually regarded as a distribution or frequency on the trapezius for the subjects who complained of shoulder stiffness, this study provides fundamental data for a technique to evaluate shoulder stiffness objectively. It is necessary to examine other factors relevant to shoulder stiffness by examining the characteristics related to and those not related to involuntary contractions. Remarkable electrical changes in the low-frequency EMG domain immediately after the end of exercise suggest a specific phenomenon occurring among subjects with shoulder stiffness. These electrical changes were in agreement with the positions of the subjective symptoms reported by the subjects. Specific muscle activity is one factor that induces shoulder stiffness and visually identifying the physiological alteration of muscle activity among subjects with shoulder stiffness is possible using myogenic topography. A part of this research was supported by Grants-in-Aid for Scientific Research Nos and [ 1 ] Ministry of Health, Labour and Welfare : Comprehensive survey of living conditions of the people on health and welfare Statistics and Information Department, Ministry of Health, Labour and Welfare, Tokyo, toukei/ saikin/ hw/ k-tyosa 07/ 3-1. html. [ 2 ] Janwantanakul P, Pensri P, Jiamjarasrangsri V, et al. : Prevalence of self-reported musculoskeletal symptoms among office workers, Occup Med, 58, , [ 3 ] Blangsted AK, Sogaard K, Hansen EA, et al. : One-year randomized controlled trial with different physical-activity programs to reduce musculoskeletal symptoms in the neck and shoulders among office workers, Scand J Work Environ Health, 34, 55-65, [ 4 ] Andersen LL, Hansen K, Mortensen OS, et al. : Prevalence and anatomical location of muscle tenderness in Vol.31 No

6 adults with nonspecific neck/shoulder pain, BMC Musculoskelet Disord, 12, 169, com/ /12/169 [ 5 ] Iijima K, Sasaki M, Katon W : Study of katakori, Nihon Ijishinnpou, 3547, 30-33, [ 6 ] Takagishi K, Hoshino Y, Ide J, et al. : Project study on katakori , J Jpn Orthop Assoc, 82, , [ 7 ] Shinozaki T, Takagishi K : Pathogenesis and symptoms of the chronic non-specific neck pain, MB Orthop, 19 4, 1-5, [ 8 ] Ito M, Imura H, Takaku H : Medical Dictionary 2nd edition, Igaku-shoin, 435, [ 9 ] Takakuwa T, Atsuta Y: Hemodynamics of Trapezius Muscle in Neck-shoulder Stiffness, Clinical Orthopaedic Surgery, 42 5, , [10] Iizuka Y, Shinozaki T, Kobayashi T, et al.: Characteristics of neck and shoulder pain called katakori in Japanese among members of the nursing staff, J Orthop Sci, 17 1, 46-50, [11] Itoh K, Kitakoji H, Kawakita K : Characteristics of spontaneous electrical activities at the trigger point in a chronic shoulder pain patient A case of trigger point on trapezius muscle, Journal of the Japan society of acupuncture and moxibustion, 54 1, , [12] Leonard JH, Kok KS, Ayiesha R, et al. : Prolonged writing task : comparison of electromyographic analysis of upper trapezius muscle in subjects with or without neck pain, Clin Ter, 161 1, 29-33, [13] Hintermeister RA, Lange GW, Schultheis JM, et al. : Electromyographic activity and applied load during shoulder rehabilitation exercises using elastic resistance, Am J Sports Med, 26 2, , [14] Ekstrom RA, Donatelli RA, Soderberg GL : Surface electromyographic analysis of exercises for the trapezius and serratus anterior muscles, J Orthop Sports Phys Ther, 33 5, , [15] Ross BH, Thomas CK : Human motor unit activity during induced muscle cramp, Brain, 118 4, , [16] Ohno M, Nosaka K : Effect of muscle fatigue and dehydration on exercise induced muscle cramp EIMC, JPN, 53, , [17] Asano Y, Atsuta Y, Yamashita I, et al. : Analyses of the pain-muscle spasm relationship and the peripheral nerve receptor activity using in vitro preparations, JPTA, , [18] Rosendal L, Larsson B, Kristiansen J, et al. : Increase in muscle nociceptive substances and anaerobic metabolism in patients with trapezius myalgia ; microdialysis in rest and during exercise, Pain, 112, , [19] Milner Brown HS, Stein RB, Yemm R: Changes in firing rate of human motor units during linearly changing voluntary contractions, J Physiol, 230, , Medical Imaging and Information Sciences