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Modulation in Elastic Properties of Upper Trapezius with Varying Neck Angle

Modulation in Elastic Properties of Upper Trapezius with Varying Neck Angle Hindawi Applied Bionics and Biomechanics Volume 2019, Article ID 6048562, 8 pages https://doi.org/10.1155/2019/6048562 Research Article Modulation in Elastic Properties of Upper Trapezius with Varying Neck Angle 1 2 1 1 3 Jun Zhang, Jiafeng Yu, Chunlong Liu, Chunzhi Tang, and Zhijie Zhang Clinical College of Acupuncture, Moxibustion, and Rehabilitation, Guangzhou University of Chinese Medicine, Guangzhou, China Department of Rehabilitation Medicine, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China Luoyang Orthopedic Hospital of Henan Province, Orthopedic Hospital of Henan Province, Luoyang, China Correspondence should be addressed to Zhijie Zhang; Sportspt@163.com Received 13 October 2018; Accepted 19 January 2019; Published 3 March 2019 Academic Editor: Thibault Lemaire Copyright © 2019 Jun Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Neck and shoulder complaints caused by poor posture may influence upper trapezius stiffness. The relationship between the shear elastic modulus of the upper trapezius and cervical flexion angles is unknown. Therefore, it is essential to assess upper trapezius stiffness during cervical flexion. The objectives of this study were to (1) determine the intra- and interoperator reliabilities of evaluating upper trapezius stiffness and calculate the minimal detectable change (MDC); (2) examine the elastic modulus alterations of the upper trapezius during cervical flexion; and (3) explore the difference of upper trapezius stiffness between the dominant and nondominant sides. Methods. Twenty healthy male participants were recruited in this study. The shear modulus of the upper trapezius was evaluated by two independent investigators using ° ° shear wave elastography (SWE) during cervical flexion at 0 and 50 . Findings. The intraoperator (intraclass correlation coefficient ICC =0 85–0.86) and interoperator (ICC = 0 94–0.98) reliabilities for measuring the shear elastic modulus of the upper trapezius during the cervical flexion ranged from good to excellent. An increase of 35.58% in upper trapezius stiffness was ° ° found at 0 to 50 of cervical flexion, and the MDC was 7.04 kPa. In addition, a significant difference was obtained in the elastic modulus of the upper trapezius muscle between the dominant and nondominant sides (P <0 05). Conclusions. Our findings revealed that SWE could quantify the elastic modulus of the upper trapezius and monitor its changes. Therefore, further studies are required to delineate the modulation in upper trapezius muscle stiffness among subjects with neck and shoulder pain. 1. Introduction biomechanical properties of the upper trapezius to further explore its biomechanical mechanism and provide stan- dard guidance in rehabilitation plans. Neck pain is a common complaint that seriously diminishes The upper trapezius muscles, as neck extensor muscles, quality of life [1, 2]. The annual incidence of neck pain now exceeds 30% [3]. Additionally, neck pain is considered a play a vital part in maintaining cervical stability despite head and neck movement. Intensive electronic device users who more general consequence of musculoskeletal disorders in certain professions than lumbar and knee discomforts [4]. assume a fixed posture for a long term are prone to develop- ing exhaustion and neck and shoulder pain [9]. The activity The upper trapezius muscle, which spans the neck and of the upper trapezius was significantly associated with neck shoulder, contributes to normal cervical vertebra and scapula motion [5]. The biomechanical properties of the upper and elbow flexion angles while using the cellphones [10]. In addition, upper trapezius fatigue became more serious dur- trapezius can be influenced among individuals with neck ° ° pain as evidenced by the significant increases in upper tra- ing neck flexion of 0 to 50 [11]. When the cervical muscles were flexed at the reextension phase, the EMG signal of the pezius activity on electromyography (EMG) and stiffness shoulder extensor muscles was sufficiently powerful [12]. by SWE [6–8]. Therefore, it is meaningful to evaluate the 2 Applied Bionics and Biomechanics Based on the findings of previous studies, the biomechanical properties of the upper trapezius were influenced by the cervical flexion angle. The biomechanical properties of the upper trapezius muscle were recently quantified using various techniques. For example, EMG is still widely used to detect muscle conditions [11, 12]. However, there are some limitations, including the source of the EMG signals being complex and the results being particularly influenced by interfer- ence between physiology, muscle tissue, external environ- mental noise, and sweating [13]. Nevertheless, SWE as a novel technology used to assess various degrees skeletal muscle stiffness is increasingly common in scientific fields [14–16] and can overcome these limitations. The principle of SWE technology is based on different shear wave velocities (V) generated by pulses in various biological tis- sues [17]. Young’s modulus (E), one shear modulus, is generally used to indirectly reflect tissue stiffness, namely, E =3ρv , in which ρ represents the tissue density. Excel- lent reliability and feasibility for assessing the deltoid, supraspinatus, and infraspinatus muscles using SWE in different positions (abduction, external rotation, and scap- tion) were reported [18]. During arm abduction, excellent intra- and interoperator reliabilities for the upper trapezius Figure 1: Participant position at 0 of cervical flexion with a stiffness were seen as evidenced by ICC > 0 78 and a stan- Goniometer Pro assessing upper trapezius stiffness. dard error of the mean SEM <6 23 kPa [19]. Further- more, SWE can be used to quantify individual neck extensor modulation during isometric contraction [20]. 2.3. Equipment. The shear modulus of the upper trapezius Therefore, SWE has the potential to estimate upper trape- muscle was quantified using the SWE with an Aixplorer zius muscle stiffness. To our knowledge, no studies have ultrasound unit (SuperSonic Imagine, Aix-en-Provence, examined the upper trapezius muscle stiffness modulation France) equipped with a 40 mm linear ultrasound transducer at different neck flexion angles. (2–10 MHz). The musculoskeletal mode was used to estimate The objectives of this study were to (1) determine the the shear modulus of the upper trapezius muscle with tempo- intra- and interoperator reliabilities of evaluating upper tra- ral averaging (persistence), penetration mode, and 85% opac- pezius elasticity and calculate the minimal detectable change; ity. The range of the color scale was adjusted from 0 to (2) examine the elastic modulus alterations of the upper tra- 200 kPa. pezius during cervical flexion; and (3) explore the difference of upper trapezius stiffness between the dominant and non- dominant sides. 2.4. SWE for Measuring Upper Trapezius Muscle. The SWE was used to quantify the upper trapezius muscle stiffness. The subjects sat on a chair with the shoulders in a neutral 2. Methods position and knees at 90 of flexion. Before testing, the partic- ipants were allowed to have a 5 min rest in a seated position. 2.1. Ethical Approval. The study was approved by the Human The cervical flexion angle was measured by a new iPhone Subject Ethics Committee of the Guangzhou University of application (Goniometer Pro) (Figure 1). Pourahmadi et al. Chinese Medicine. The experimental procedures were fully measured cervical flexion angles using Goniometer Pro and explained to each subject before the study. All subjects pro- reported good reliability: ICC > 0 65, SEM < 3 11 , and vided written informed consent prior to the experiment, MDC < 8 62 [21]. In our study, 10 subjects were recruited and all of the study procedures adhered to the principles of to calculate Goniometer Pro reliability during 50 of cervical the Declaration of Helsinki. ° ° flexion: ICC > 0 71, SEM < 0 61 , and MDC < 1 96 . The measurement sites were marked with a marker at the mid- 2.2. Subjects. Twenty healthy male subjects from Luoyang point between the seventh cervical spinous process and the Orthopedic-Traumatological Hospital participated in this acromion [22]. The marked site for each subject was cleaned study. Age, height, weight, body mass index (BMI), and after the experiment. Before the scanning, ultrasound gel was weekly exercise time of each subject were recorded. The applied to the skin around the probe location. On the subjects were prohibited from exercising for 48 h before B-mode image, the probe was placed perpendicularly to the the experiment. Subjects with a history of neck or shoul- skin and slightly adjusted so it was parallel to the upper tra- der pain, orthopedic disease, or upper-limb neuropathy pezius muscle fibers to obtain a clear image. Once an image were excluded. without a muscle anisotropic artifact was determined, we Applied Bionics and Biomechanics 3 (a) (b) Figure 2: SWE maps of the upper trapezius muscle. Upper images: color-coded box presentations of the upper trapezius elasticity are shown in the upper image (the image color represents stiffness degree: red indicates stiff, while blue indicates soft). Lower images: B-mode images of the upper trapezius (UT: upper trapezius). Table 1: Subjects’ demographic information (N =20 male subjects). switched to E mode to quantify the elastic modulus of the upper trapezius muscle (Figure 2). The size of the circular Mean ± SD regions of interest (ROIs) was defined as the thickness of 23 1±2 7 Age (years) the upper trapezius [22]. The mean value of three measure- ments was used in this study. 70 6±9 9 Weight (kg) The bilateral sides of the elastic modulus of the upper tra- 1 74 ± 0 04 Height (m) pezius muscle were estimated using SWE. The dominant side 23 4±2 7 Body mass index (kg/m ) was subjected to the intra- and interoperator reliability tests. 2 8±2 3 Weekly exercise hours To assess intraoperator reliability, all subjects were examined ° ° by operator A (ZJ) using SWE at 0 and 50 of neck flexion. SD, standard deviation. The same subjects were evaluated again by operator A (ZJ) (standard deviation), and values of P <0 05 were consid- 5 days later. For the evaluation of interoperator reliability, ered statistically significant. all subjects were assessed by both operators (ZJ and ZJP) once at 30 min intervals. The operators were blinded to the measurement results during the test. After completing the 3. Results measurement task at each angle, the participants were 3.1. Demographic Data. Demographic information including allowed to relax for 2 mins. age, weight, height, BMI, and weekly exercise hours for all 2.5. Statistical Analysis. SPSS version 19.0 software (SPSS subjects are shown in Table 1. All subjects were able to Inc., Chicago, IL, USA) was used to perform the statistical complete the action of cervical flexion without discomfort analyses. The demographic information was calculated by under the guidance of the operators. descriptive statistics. A paired t-test was performed to com- pare the mean elastic moduli of the upper trapezius muscle 3.2. Intra- and Interoperator Reliabilities. The related statisti- ° ° between 0 and 50 of cervical flexion and verify the differ- cal parameters for intra- and interoperator reliabilities for ences between the elastic moduli of the upper trapezius assessing upper trapezius muscle stiffness of the dominant muscle between the dominant and nondominant sides. shoulder are summarized in Table 2. The mean stiffness Intra- and interoperator reliabilities were determined by values of the upper trapezius were 40.47 kPa for operator A the calculation of the intraclass correlation coefficient in test 1, 39.90 kPa for operator A in test 2, and 41.01 kPa (ICC) with 95% confidence interval. The intraoperator reli- for operator B during the cervical flexion at 0 . The mean ability was evaluated using the ICC (3,1) (two-way stiffness values of the upper trapezius were 62.83 kPa for mixed-effect model, consistency), and the interoperator operator A in test 1, 64.12 kPa for operator A in test 2, and reliability was assessed using the ICC (2,2) (two-way 63.20 kPa for operator B during the cervical flexion at 50 . random effects model, absolute agreement). The standard The ICC values of intraoperator reliability were good in the error of measurement (SEM) was computed by the formula context of cervical flexion at 0 (ICC = 0 86; 95% CI = 0 69– SEM = standard deviation × 1 − ICC, while the MDC was 0.94; SEM < 2 59 kPa; and MDC < 7 20 kPa) and cervical calculated by the formula MDC = 1 96 × SEM × 2. Bland flexion at 50 (ICC = 0 85; 95% CI = 0 67–0.94; SEM < 5 01 and Altman plots further intuitively indicated the degree kPa; and MDC < 13 89 kPa). The ICC values of interoperator of agreement for assessing intra- and interoperator reliabil- reliability were excellent in the context of 0 of cervical ities. All measurement data are expressed as mean flexion (ICC = 0 98; 95% CI = 0 96–0.99; SEM < 2 69 kPa; 4 Applied Bionics and Biomechanics Table 2: Intra- and interrater reliabilities of SWE for assessing upper trapezius muscle stiffness. ° ° Cervical flexion at 0 Cervical flexion at 50 Mean ± SD SEM MDC Mean ± SD SEM MDC 40 47 ± 11 37 62 83 ± 22 42 Operator A in test 1 2.54 7.04 5.01 13.89 Operator A in test 2 39 90 ± 11 62 2.59 7.20 64 12 ± 19 58 4.37 12.13 41 01 ± 12 07 63 20 ± 21 77 Operator B 2.69 7.48 4.86 13.49 ICC (95% CI) 0.86 (0.69–0.94) 0.85 (0.67–0.94) ICC (95% CI) 0.98 (0.96–0.99) 0.94 (0.86–0.97) ICC, intraclass correlation coefficient; CI, confidence interval; SEM (kPa), standard error of measurement of kPa; MDC (kPa), minimal detectable change; SD a b (kPa), standard deviation of kPa; kPa, kilo Pascal. Intraoperator reliability; Interoperator reliability. +1.96 SD 11.3 +1.96 SD 4.16 Mean Mean -0.57 0.54 -4 -1 -8 -2 -1.96 SD -1.96 SD -12 -3 -12.5 -3.07 -16 -4 24 30 39 42 48 54 60 66 72 24 30 39 42 48 54 60 66 72 Mean stiffness (kPa) Mean stiffness (kPa) (a) (b) +1.96 SD 20 +1.96 SD 23.7 20 15 15.4 Mean Mean 0 1.29 0 0.37 -5 -10 -10 -1.96 SD -1.96 SD -20 -15 -14.47 -21.1 -20 30 45 60 75 90 105 120 135 30 45 60 75 90 105 120 135 Mean stiffness (kPa) Mean stiffness (kPa) (c) (d) Figure 3: Bland-Altman plots of intra- and interoperator reliabilities for measuring the upper trapezius at 0 of cervical flexion. (a, b) Intra- and interoperator reliabilities of assessing upper trapezius stiffness at 0 of cervical flexion. (c, d) Intra- and interoperator reliabilities of assessing upper trapezius stiffness at 50 of cervical flexion (the continuous lines represent the mean difference, while the dotted lines show the 95% upper and lower limits of agreement). and MDC < 7 48 kPa) and 50 of cervical flexion shown in Figures 3(c) and 3(d). The mean difference was (ICC = 0 94; 95% CI = 0 86–0.97; SEM < 5 01 kPa; and 1.29 or 0.37 kPa and the 95% limits of agreement were MDC < 13 89 kPa). -21.1 to 23.7 kPa or -14.7 to 15.4 kPa. Bland and Altman plots of intra- and interoperator reliabilities with 0 of cervical flexion are shown in 3.3. Changes in Upper Trapezius Stiffness during Cervical Figures 3(a) and 3(b). The mean difference was -0.57 or Flexion. The mean upper trapezius stiffness value was 4.16 kPa, and the 95% limits of agreement were -12.5 to 40.47 kPa at 0 of cervical flexion. By comparison, the stiff- 11.3 kPa or -3.07 to 4.16 kPa. Other plots of intra- and ness was 60.83 kPa at 50 of cervical flexion (P ≤ 0 001), with interoperator reliabilities at 50 of cervical flexion are an increase of 35.58% (Figure 4). Difference (kPa) Difference (kPa) Difference (kPa) Difference (kPa) Applied Bionics and Biomechanics 5 100 100 Dominant upper trapezius 80 ⁎⁎ 80 ⁎ 60 60 40 40 20 20 0 0 Angles of cervical (°) Angles of cervical (°) Dominant upper trapezius Figure 4: Mean and standard deviation of upper trapezius shear ° ° Non-Dominant upper trapezius modulus examined during 0 (white bar) or 50 (gray bar) of cervical flexion. Significant intergroup difference (P <0 05). Figure 5: Mean and standard deviation in upper trapezius shear modulus examined between the dominant (white bar) and 3.4. Differences of Upper Trapezius Stiffness between the ° ° nondominant (gray bar) sides during 0 and 50 of cervical flexion. Dominant and Nondominant Sides. At 0 of cervical flexion, Significant intergroup difference (P <0 05). there was a significant difference in the elastic modulus of the upper trapezius between the dominant (40.47 kPa) and nondominant (35.25 kPa) sides (P ≤ 0 001). During 50 of use of different instruments for assessing the upper trapezius. No study of the reliability of assessing the upper trapezius at cervical flexion, a significant difference in the elastic modulus of the upper trapezius muscle was found between the 50 of neck flexion is available to enable a comparison. The dominant (62.83 kPa) and nondominant (55.21 kPa) sides intra- and interoperator reliabilities of assessing other skele- (P ≤ 0 001) (Figure 5). tal muscles using SWE were excellent. All regions of supras- pinatus muscle elasticity were quantified by SWE and showed satisfactory intra- and interobserver reliabilities: 4. Discussion ICC = 0 945–0.970 or ICC = 0 882–0.948 [24]. Only intraoperator reliability (ICC ≥ 0 90) was used to evaluate SWE is a feasible instrument for assessing the shear mod- ulus of the upper trapezius at different cervical degrees. the pectoralis minor muscle in six different positions [25]. To summarize, SWE is a highly repeatable technique for We noted excellent intra- and interoperator reliabilities for evaluating upper trapezius stiffness via SWE with rela- quantifying muscle elasticity. tively low SEM and MDC values. A significant difference In our study, the ICC values for interoperator reliability were relatively high compared to those of intraoperator reli- was obtained in upper trapezius stiffness between the 0 and 50 of neck flexion. We also noted a significant difference ability. Considering possible explanations for these differ- in upper trapezius muscle stiffness between the dominant ences, we considered that the 5-day interval from the first measurement might have been a dominant factor, as the and nondominant sides. amount of exercise and other external factors in this 5-day 4.1. Intra- and Interoperator Reliabilities. In the present period may have influenced the experiment’s accuracy. The study, intraoperator reliability was good for assessing the ICC value for 0 of cervical flexion may have been superior ° ° upper trapezius at 0 of cervical flexion (ICC = 0 86) and to that of 50 of cervical flexion due to measurement errors. ° ° 50 of cervical flexion (ICC = 0 85), but the interoperator reli- In comparison to keeping the cervical flexion at 0 , maintain- ° ° ° ability at 0 of cervical flexion (ICC = 0 98) and 50 of cervical ing a cervical flexion of 50 according to the Goniometer Pro flexion (ICC = 0 94) was excellent. Our findings were rela- was difficult as holding the cervical flexion at relatively higher tively consistent with those of previous studies evaluating degrees of flexion accurately was difficult, and thus, the error skeletal muscles. SWE was used to assess the upper trapezius of measuring the flexion angles in such cases cannot be with the arm at rest and at 30 ignored. The findings from this study have indicated that of abduction [19]. The intrao- perator (ICC = 0 87) and interoperator (ICC = 0 78) reliabil- the SWE is a credible instrument for evaluating upper ities were good with the arm at rest, corresponding to the trapezius stiffness. SEM < 6 23 kPa and MDC < 17 26 kPa. One study revealed The Bland-Altman plots of our study data further verified the same ICC values (ICC = 0 97) for intra- and interopera- the consistency of our findings. It is clinically acceptable to obtain measurement differences within the limits of agree- tor reliabilities of assessing the upper trapezius using the Myoton PRO with the shoulder in a neutral position [23]. ment [26]. As seen in Figure 3, almost all of the data points One possible reason for the higher ICC values for intraopera- were within the 95% confidence limit. Therefore, the consis- tor reliability than those in our study may be related to the tency of our study data is satisfactory. UT elastic modulus (kPa) UT elastic modulus (kPa) 6 Applied Bionics and Biomechanics stiffness using a Myoton PRO and reported that upper 4.2. Alterations in Upper Trapezius Stiffness during Cervical Flexion. The shear elastic modulus of the upper trapezius trapezius stiffness was significantly reduced by 5.5 N/m after muscle during cervical flexion was quantified using SWE in cervical traction. Furthermore, massage therapy is also a this study. Our results demonstrated that the mean shear good way to relieve pain and tension, as a 19.3% decrease modulus of the upper trapezius at 0 of cervical flexion was in upper trapezius activity was measured by EMG after 40.47 kPa; this value increased to 62.83 kPa at 50 of cervical massage treatment [29]. flexion. Also, the change in the shear modulus was greater The MDC was calculated to detect true changes. In our than the MDC (7.04 kPa), indicating true changes. This is study, the elastic modulus of the upper trapezius should have the first study to examine the effect of different neck positions been greater than 7.04 kPa with different operators to reveal on the elastic modulus of the upper trapezius muscle. It is dif- the true changes with reassessed measurements. ficult to directly compare our findings to those of previous studies. However, previous studies investigated the effect of 4.3. Differences in Upper Trapezius Stiffness between the various shoulder positions on the elastic modulus of the Dominant and Nondominant Sides. Here, we found a signif- upper trapezius muscle. For example, using SWE, Leong icant difference in the elastic modulus of the upper trapezius et al. [19] reported that the elastic modulus of the upper tra- between the dominant and nondominant sides. The high pezius muscle was influenced by shoulder abduction, specify- utilization of the dominant versus the nondominant side ing an increase of 55.23% of shear elastic modulus during may contribute to the long-term usage of the extensor ° ° arm positions of 0 to 30 of abduction. In addition, our muscles, which reasonably explains the differences in stiff- ness. Uthaikhup et al. [30] examined the thickness of the recent study demonstrated that shoulder flexion could affect upper trapezius stiffness using a handheld Myoton PRO lower trapezius and found greater lower trapezius muscle device. We also found a 14.2% increase in upper trapezius thickness on the dominant versus the nondominant side ° ° stiffness at 0 to 60 of shoulder flexion [23]. In addition, of 0 43 ± 0 02 mm. Fatigue of the upper trapezius also dif- using SWE, Maher et al. [27] reported that the elastic fered bilaterally; the upper trapezius on the dominant side modulus of the upper trapezius was affected by a posture was less fatigable by surface EMG [31]. These results were change. Specifically, they reported a 12.2% increase with similar to our findings, which might support the notion of a change from a prone to a sitting position. In another long-term usage of the extensor muscles on the dominant study, an increase in upper trapezius activity was detected side. However, another study reported no significant dif- among smart phone users. The fatigue of the upper trapezius ference in muscle fatigue between the dominant and non- assessed by EMG during cervical flexion revealed a value of dominant sides [11]. The different results might be caused −0 2±1 3Hz at 0 of neck flexion that increased to −3 5± by differences between studies, such as those associated 5 6Hz at 50 of neck flexion [11]. Here, we found an increase with the participant sex, age, and work experience. There- of 35.58% in the elastic modulus of the upper trapezius with a fore, the stiffer upper trapezius on the dominant side ° ° change from 0 to 50 of cervical flexion. might lead to a higher risk of neck and shoulder pain The upper trapezius, as a neck extensor muscle, main- compared to the nondominant side. Our findings could tains cervical spine stability. The external flexion torque be useful in the prevention of neck and shoulder pain, and we should consider the differences in the shear elastic caused by cervical flexion has a significant effect, directly increasing the extensor muscle load. Moreover, muscle over- moduli of the upper trapezius between the dominant and load in a poor posture can easily lead to pathological changes nondominant sides. to the neck and shoulder, while upper trapezius stiffness SWE, a new technique that provides relatively standard can significantly increase among people with neck and elastic parameters of biological tissues, has high accuracy shoulder disorders. For example, using SWE, Leong et al. and sensitivity, features good repeatability, and is a simple [7] demonstrated a 20% stiffer upper trapezius among operative method that measures muscle elasticity from the subjects with rotator cuff tendinopathy compared with that initial qualitative assessment to the quantitative assessment. in healthy subjects. Ishikawa et al. [8] reported an SWE has been widely used in healthy individuals for muscle increased upper trapezius stiffness among people with assessments as well as in biomechanical studies [19, 32, 33]. neck and shoulder complaints compared with healthy sub- Previous comparisons of SWE and a muscle hardness meter jects. Therefore, the 35.58% increase in the shear modulus showed that the former more precisely evaluated neck and of the upper trapezius during cervical flexion noted in our shoulder muscle stiffness [34]. Moreover, assessing alter- study further verifies that poor posture may be a risk ations in supraspinatus stiffness after a margin convergence factor for neck and shoulder complaints. technique using SWE contributed to a deeper insight into Furthermore, recent studies suggested that many thera- the biomechanical effect on the repaired supraspinatus and pies could decrease upper trapezius stiffness. One study provided a scientific and reasonable rehabilitation plan found that dry needling could be used to reduce the elastic [35]. Thus, SWE is expected to be an effective measurement modulus of the upper trapezius, reporting a 12.8% reduction tool for quantitatively evaluating the musculoskeletal system in the elastic modulus of the upper trapezius pre- versus post- under various physiological and pathological conditions. treatment [27]. Cervical traction is a good way to relieve neck discomfort. Sung-Yong and Jung-Hyun [28] examined the 4.4. Limitations. This study had some limitations. First, only influence of three therapies (cervical traction, cranial rhyth- male subjects were included; therefore, sex-based differences mic impulse, and McKenzie exercise) on upper trapezius could not be evaluated. Muscle discomfort caused by a Applied Bionics and Biomechanics 7 [9] U. H. M. Rasim, S. S. Ali, A. Rasheed, and M. Khan, “Fre- computer test was more pronounced in male subjects in a quency and associated risk factors for neck pain among previous study [36]. Further studies of the biomechanical software engineers in Karachi, Pakistan,” Journal of Pakistan characteristics of the upper trapezius of females are required. Medical Students, vol. 67, no. 7, pp. 1009–1012, 2017. Second, we measured only one site of the upper trapezius; [10] P. H. Ko, Y. H. Hwang, and H. W. Liang, “Influence of smart- however, this cannot reflect the entire upper trapezius. It will phone use styles on typing performance and biomechanical be worth exploring the differences in stiffness values in differ- exposure,” Ergonomics, vol. 59, no. 6, pp. 821–828, 2016. ent parts of the upper trapezius in the future. Third, all [11] S. Lee, D. Lee, and J. Park, “Effect of the cervical flexion angle recruited subjects had no neck or shoulder complaints; there- during smart phone use on muscle fatigue of the cervical fore, a subsequent experiment will focus on assessing modu- erector spinae and upper trapezius,” Journal of Physical lations in upper trapezius stiffness using SWE for people who Therapy Science, vol. 27, no. 6, pp. 1847–1849, 2015. suffer from neck and shoulder pain. [12] S. J. Shin, D. H. An, J. S. Oh, and W. G. Yoo, “Changes in pres- sure pain in the upper trapezius muscle, cervical range of 5. Conclusions motion, and the cervical flexion-relaxation ratio after overhead work,” Industrial Health, vol. 50, no. 6, pp. 509–515, 2012. SWE is a potential tool for assessing upper trapezius elasticity [13] C. Disselhorstklug, T. Schmitzrode, and G. Rau, “Surface with satisfactory reliability. Further studies should investigate electromyography and muscle force: limits in sEMG-force the biomechanical properties of the upper trapezius using relationship and new approaches for applications,” Clinical SWE among people with neck and shoulder complaints. biomechanics, vol. 24, no. 3, pp. 225–235, 2009. [14] T. Hatta, H. Giambini, Y. Itoigawa et al., “Quantifying extensi- Data Availability bility of rotator cuff muscle with tendon rupture using shear wave elastography: a cadaveric study,” Journal of Biomechan- All data included in this study are available upon request ics, vol. 61, pp. 131–136, 2017. from the corresponding author. [15] M. S. Taljanovic, L. H. Gimber, G. W. Becker et al., “Shear-wave elastography: basic physics and musculoskeletal applications,” Radiographics, vol. 37, no. 3, pp. 855–870, 2017. 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Modulation in Elastic Properties of Upper Trapezius with Varying Neck Angle

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Copyright © 2019 Jun Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Hindawi Applied Bionics and Biomechanics Volume 2019, Article ID 6048562, 8 pages https://doi.org/10.1155/2019/6048562 Research Article Modulation in Elastic Properties of Upper Trapezius with Varying Neck Angle 1 2 1 1 3 Jun Zhang, Jiafeng Yu, Chunlong Liu, Chunzhi Tang, and Zhijie Zhang Clinical College of Acupuncture, Moxibustion, and Rehabilitation, Guangzhou University of Chinese Medicine, Guangzhou, China Department of Rehabilitation Medicine, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China Luoyang Orthopedic Hospital of Henan Province, Orthopedic Hospital of Henan Province, Luoyang, China Correspondence should be addressed to Zhijie Zhang; Sportspt@163.com Received 13 October 2018; Accepted 19 January 2019; Published 3 March 2019 Academic Editor: Thibault Lemaire Copyright © 2019 Jun Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Neck and shoulder complaints caused by poor posture may influence upper trapezius stiffness. The relationship between the shear elastic modulus of the upper trapezius and cervical flexion angles is unknown. Therefore, it is essential to assess upper trapezius stiffness during cervical flexion. The objectives of this study were to (1) determine the intra- and interoperator reliabilities of evaluating upper trapezius stiffness and calculate the minimal detectable change (MDC); (2) examine the elastic modulus alterations of the upper trapezius during cervical flexion; and (3) explore the difference of upper trapezius stiffness between the dominant and nondominant sides. Methods. Twenty healthy male participants were recruited in this study. The shear modulus of the upper trapezius was evaluated by two independent investigators using ° ° shear wave elastography (SWE) during cervical flexion at 0 and 50 . Findings. The intraoperator (intraclass correlation coefficient ICC =0 85–0.86) and interoperator (ICC = 0 94–0.98) reliabilities for measuring the shear elastic modulus of the upper trapezius during the cervical flexion ranged from good to excellent. An increase of 35.58% in upper trapezius stiffness was ° ° found at 0 to 50 of cervical flexion, and the MDC was 7.04 kPa. In addition, a significant difference was obtained in the elastic modulus of the upper trapezius muscle between the dominant and nondominant sides (P <0 05). Conclusions. Our findings revealed that SWE could quantify the elastic modulus of the upper trapezius and monitor its changes. Therefore, further studies are required to delineate the modulation in upper trapezius muscle stiffness among subjects with neck and shoulder pain. 1. Introduction biomechanical properties of the upper trapezius to further explore its biomechanical mechanism and provide stan- dard guidance in rehabilitation plans. Neck pain is a common complaint that seriously diminishes The upper trapezius muscles, as neck extensor muscles, quality of life [1, 2]. The annual incidence of neck pain now exceeds 30% [3]. Additionally, neck pain is considered a play a vital part in maintaining cervical stability despite head and neck movement. Intensive electronic device users who more general consequence of musculoskeletal disorders in certain professions than lumbar and knee discomforts [4]. assume a fixed posture for a long term are prone to develop- ing exhaustion and neck and shoulder pain [9]. The activity The upper trapezius muscle, which spans the neck and of the upper trapezius was significantly associated with neck shoulder, contributes to normal cervical vertebra and scapula motion [5]. The biomechanical properties of the upper and elbow flexion angles while using the cellphones [10]. In addition, upper trapezius fatigue became more serious dur- trapezius can be influenced among individuals with neck ° ° pain as evidenced by the significant increases in upper tra- ing neck flexion of 0 to 50 [11]. When the cervical muscles were flexed at the reextension phase, the EMG signal of the pezius activity on electromyography (EMG) and stiffness shoulder extensor muscles was sufficiently powerful [12]. by SWE [6–8]. Therefore, it is meaningful to evaluate the 2 Applied Bionics and Biomechanics Based on the findings of previous studies, the biomechanical properties of the upper trapezius were influenced by the cervical flexion angle. The biomechanical properties of the upper trapezius muscle were recently quantified using various techniques. For example, EMG is still widely used to detect muscle conditions [11, 12]. However, there are some limitations, including the source of the EMG signals being complex and the results being particularly influenced by interfer- ence between physiology, muscle tissue, external environ- mental noise, and sweating [13]. Nevertheless, SWE as a novel technology used to assess various degrees skeletal muscle stiffness is increasingly common in scientific fields [14–16] and can overcome these limitations. The principle of SWE technology is based on different shear wave velocities (V) generated by pulses in various biological tis- sues [17]. Young’s modulus (E), one shear modulus, is generally used to indirectly reflect tissue stiffness, namely, E =3ρv , in which ρ represents the tissue density. Excel- lent reliability and feasibility for assessing the deltoid, supraspinatus, and infraspinatus muscles using SWE in different positions (abduction, external rotation, and scap- tion) were reported [18]. During arm abduction, excellent intra- and interoperator reliabilities for the upper trapezius Figure 1: Participant position at 0 of cervical flexion with a stiffness were seen as evidenced by ICC > 0 78 and a stan- Goniometer Pro assessing upper trapezius stiffness. dard error of the mean SEM <6 23 kPa [19]. Further- more, SWE can be used to quantify individual neck extensor modulation during isometric contraction [20]. 2.3. Equipment. The shear modulus of the upper trapezius Therefore, SWE has the potential to estimate upper trape- muscle was quantified using the SWE with an Aixplorer zius muscle stiffness. To our knowledge, no studies have ultrasound unit (SuperSonic Imagine, Aix-en-Provence, examined the upper trapezius muscle stiffness modulation France) equipped with a 40 mm linear ultrasound transducer at different neck flexion angles. (2–10 MHz). The musculoskeletal mode was used to estimate The objectives of this study were to (1) determine the the shear modulus of the upper trapezius muscle with tempo- intra- and interoperator reliabilities of evaluating upper tra- ral averaging (persistence), penetration mode, and 85% opac- pezius elasticity and calculate the minimal detectable change; ity. The range of the color scale was adjusted from 0 to (2) examine the elastic modulus alterations of the upper tra- 200 kPa. pezius during cervical flexion; and (3) explore the difference of upper trapezius stiffness between the dominant and non- dominant sides. 2.4. SWE for Measuring Upper Trapezius Muscle. The SWE was used to quantify the upper trapezius muscle stiffness. The subjects sat on a chair with the shoulders in a neutral 2. Methods position and knees at 90 of flexion. Before testing, the partic- ipants were allowed to have a 5 min rest in a seated position. 2.1. Ethical Approval. The study was approved by the Human The cervical flexion angle was measured by a new iPhone Subject Ethics Committee of the Guangzhou University of application (Goniometer Pro) (Figure 1). Pourahmadi et al. Chinese Medicine. The experimental procedures were fully measured cervical flexion angles using Goniometer Pro and explained to each subject before the study. All subjects pro- reported good reliability: ICC > 0 65, SEM < 3 11 , and vided written informed consent prior to the experiment, MDC < 8 62 [21]. In our study, 10 subjects were recruited and all of the study procedures adhered to the principles of to calculate Goniometer Pro reliability during 50 of cervical the Declaration of Helsinki. ° ° flexion: ICC > 0 71, SEM < 0 61 , and MDC < 1 96 . The measurement sites were marked with a marker at the mid- 2.2. Subjects. Twenty healthy male subjects from Luoyang point between the seventh cervical spinous process and the Orthopedic-Traumatological Hospital participated in this acromion [22]. The marked site for each subject was cleaned study. Age, height, weight, body mass index (BMI), and after the experiment. Before the scanning, ultrasound gel was weekly exercise time of each subject were recorded. The applied to the skin around the probe location. On the subjects were prohibited from exercising for 48 h before B-mode image, the probe was placed perpendicularly to the the experiment. Subjects with a history of neck or shoul- skin and slightly adjusted so it was parallel to the upper tra- der pain, orthopedic disease, or upper-limb neuropathy pezius muscle fibers to obtain a clear image. Once an image were excluded. without a muscle anisotropic artifact was determined, we Applied Bionics and Biomechanics 3 (a) (b) Figure 2: SWE maps of the upper trapezius muscle. Upper images: color-coded box presentations of the upper trapezius elasticity are shown in the upper image (the image color represents stiffness degree: red indicates stiff, while blue indicates soft). Lower images: B-mode images of the upper trapezius (UT: upper trapezius). Table 1: Subjects’ demographic information (N =20 male subjects). switched to E mode to quantify the elastic modulus of the upper trapezius muscle (Figure 2). The size of the circular Mean ± SD regions of interest (ROIs) was defined as the thickness of 23 1±2 7 Age (years) the upper trapezius [22]. The mean value of three measure- ments was used in this study. 70 6±9 9 Weight (kg) The bilateral sides of the elastic modulus of the upper tra- 1 74 ± 0 04 Height (m) pezius muscle were estimated using SWE. The dominant side 23 4±2 7 Body mass index (kg/m ) was subjected to the intra- and interoperator reliability tests. 2 8±2 3 Weekly exercise hours To assess intraoperator reliability, all subjects were examined ° ° by operator A (ZJ) using SWE at 0 and 50 of neck flexion. SD, standard deviation. The same subjects were evaluated again by operator A (ZJ) (standard deviation), and values of P <0 05 were consid- 5 days later. For the evaluation of interoperator reliability, ered statistically significant. all subjects were assessed by both operators (ZJ and ZJP) once at 30 min intervals. The operators were blinded to the measurement results during the test. After completing the 3. Results measurement task at each angle, the participants were 3.1. Demographic Data. Demographic information including allowed to relax for 2 mins. age, weight, height, BMI, and weekly exercise hours for all 2.5. Statistical Analysis. SPSS version 19.0 software (SPSS subjects are shown in Table 1. All subjects were able to Inc., Chicago, IL, USA) was used to perform the statistical complete the action of cervical flexion without discomfort analyses. The demographic information was calculated by under the guidance of the operators. descriptive statistics. A paired t-test was performed to com- pare the mean elastic moduli of the upper trapezius muscle 3.2. Intra- and Interoperator Reliabilities. The related statisti- ° ° between 0 and 50 of cervical flexion and verify the differ- cal parameters for intra- and interoperator reliabilities for ences between the elastic moduli of the upper trapezius assessing upper trapezius muscle stiffness of the dominant muscle between the dominant and nondominant sides. shoulder are summarized in Table 2. The mean stiffness Intra- and interoperator reliabilities were determined by values of the upper trapezius were 40.47 kPa for operator A the calculation of the intraclass correlation coefficient in test 1, 39.90 kPa for operator A in test 2, and 41.01 kPa (ICC) with 95% confidence interval. The intraoperator reli- for operator B during the cervical flexion at 0 . The mean ability was evaluated using the ICC (3,1) (two-way stiffness values of the upper trapezius were 62.83 kPa for mixed-effect model, consistency), and the interoperator operator A in test 1, 64.12 kPa for operator A in test 2, and reliability was assessed using the ICC (2,2) (two-way 63.20 kPa for operator B during the cervical flexion at 50 . random effects model, absolute agreement). The standard The ICC values of intraoperator reliability were good in the error of measurement (SEM) was computed by the formula context of cervical flexion at 0 (ICC = 0 86; 95% CI = 0 69– SEM = standard deviation × 1 − ICC, while the MDC was 0.94; SEM < 2 59 kPa; and MDC < 7 20 kPa) and cervical calculated by the formula MDC = 1 96 × SEM × 2. Bland flexion at 50 (ICC = 0 85; 95% CI = 0 67–0.94; SEM < 5 01 and Altman plots further intuitively indicated the degree kPa; and MDC < 13 89 kPa). The ICC values of interoperator of agreement for assessing intra- and interoperator reliabil- reliability were excellent in the context of 0 of cervical ities. All measurement data are expressed as mean flexion (ICC = 0 98; 95% CI = 0 96–0.99; SEM < 2 69 kPa; 4 Applied Bionics and Biomechanics Table 2: Intra- and interrater reliabilities of SWE for assessing upper trapezius muscle stiffness. ° ° Cervical flexion at 0 Cervical flexion at 50 Mean ± SD SEM MDC Mean ± SD SEM MDC 40 47 ± 11 37 62 83 ± 22 42 Operator A in test 1 2.54 7.04 5.01 13.89 Operator A in test 2 39 90 ± 11 62 2.59 7.20 64 12 ± 19 58 4.37 12.13 41 01 ± 12 07 63 20 ± 21 77 Operator B 2.69 7.48 4.86 13.49 ICC (95% CI) 0.86 (0.69–0.94) 0.85 (0.67–0.94) ICC (95% CI) 0.98 (0.96–0.99) 0.94 (0.86–0.97) ICC, intraclass correlation coefficient; CI, confidence interval; SEM (kPa), standard error of measurement of kPa; MDC (kPa), minimal detectable change; SD a b (kPa), standard deviation of kPa; kPa, kilo Pascal. Intraoperator reliability; Interoperator reliability. +1.96 SD 11.3 +1.96 SD 4.16 Mean Mean -0.57 0.54 -4 -1 -8 -2 -1.96 SD -1.96 SD -12 -3 -12.5 -3.07 -16 -4 24 30 39 42 48 54 60 66 72 24 30 39 42 48 54 60 66 72 Mean stiffness (kPa) Mean stiffness (kPa) (a) (b) +1.96 SD 20 +1.96 SD 23.7 20 15 15.4 Mean Mean 0 1.29 0 0.37 -5 -10 -10 -1.96 SD -1.96 SD -20 -15 -14.47 -21.1 -20 30 45 60 75 90 105 120 135 30 45 60 75 90 105 120 135 Mean stiffness (kPa) Mean stiffness (kPa) (c) (d) Figure 3: Bland-Altman plots of intra- and interoperator reliabilities for measuring the upper trapezius at 0 of cervical flexion. (a, b) Intra- and interoperator reliabilities of assessing upper trapezius stiffness at 0 of cervical flexion. (c, d) Intra- and interoperator reliabilities of assessing upper trapezius stiffness at 50 of cervical flexion (the continuous lines represent the mean difference, while the dotted lines show the 95% upper and lower limits of agreement). and MDC < 7 48 kPa) and 50 of cervical flexion shown in Figures 3(c) and 3(d). The mean difference was (ICC = 0 94; 95% CI = 0 86–0.97; SEM < 5 01 kPa; and 1.29 or 0.37 kPa and the 95% limits of agreement were MDC < 13 89 kPa). -21.1 to 23.7 kPa or -14.7 to 15.4 kPa. Bland and Altman plots of intra- and interoperator reliabilities with 0 of cervical flexion are shown in 3.3. Changes in Upper Trapezius Stiffness during Cervical Figures 3(a) and 3(b). The mean difference was -0.57 or Flexion. The mean upper trapezius stiffness value was 4.16 kPa, and the 95% limits of agreement were -12.5 to 40.47 kPa at 0 of cervical flexion. By comparison, the stiff- 11.3 kPa or -3.07 to 4.16 kPa. Other plots of intra- and ness was 60.83 kPa at 50 of cervical flexion (P ≤ 0 001), with interoperator reliabilities at 50 of cervical flexion are an increase of 35.58% (Figure 4). Difference (kPa) Difference (kPa) Difference (kPa) Difference (kPa) Applied Bionics and Biomechanics 5 100 100 Dominant upper trapezius 80 ⁎⁎ 80 ⁎ 60 60 40 40 20 20 0 0 Angles of cervical (°) Angles of cervical (°) Dominant upper trapezius Figure 4: Mean and standard deviation of upper trapezius shear ° ° Non-Dominant upper trapezius modulus examined during 0 (white bar) or 50 (gray bar) of cervical flexion. Significant intergroup difference (P <0 05). Figure 5: Mean and standard deviation in upper trapezius shear modulus examined between the dominant (white bar) and 3.4. Differences of Upper Trapezius Stiffness between the ° ° nondominant (gray bar) sides during 0 and 50 of cervical flexion. Dominant and Nondominant Sides. At 0 of cervical flexion, Significant intergroup difference (P <0 05). there was a significant difference in the elastic modulus of the upper trapezius between the dominant (40.47 kPa) and nondominant (35.25 kPa) sides (P ≤ 0 001). During 50 of use of different instruments for assessing the upper trapezius. No study of the reliability of assessing the upper trapezius at cervical flexion, a significant difference in the elastic modulus of the upper trapezius muscle was found between the 50 of neck flexion is available to enable a comparison. The dominant (62.83 kPa) and nondominant (55.21 kPa) sides intra- and interoperator reliabilities of assessing other skele- (P ≤ 0 001) (Figure 5). tal muscles using SWE were excellent. All regions of supras- pinatus muscle elasticity were quantified by SWE and showed satisfactory intra- and interobserver reliabilities: 4. Discussion ICC = 0 945–0.970 or ICC = 0 882–0.948 [24]. Only intraoperator reliability (ICC ≥ 0 90) was used to evaluate SWE is a feasible instrument for assessing the shear mod- ulus of the upper trapezius at different cervical degrees. the pectoralis minor muscle in six different positions [25]. To summarize, SWE is a highly repeatable technique for We noted excellent intra- and interoperator reliabilities for evaluating upper trapezius stiffness via SWE with rela- quantifying muscle elasticity. tively low SEM and MDC values. A significant difference In our study, the ICC values for interoperator reliability were relatively high compared to those of intraoperator reli- was obtained in upper trapezius stiffness between the 0 and 50 of neck flexion. We also noted a significant difference ability. Considering possible explanations for these differ- in upper trapezius muscle stiffness between the dominant ences, we considered that the 5-day interval from the first measurement might have been a dominant factor, as the and nondominant sides. amount of exercise and other external factors in this 5-day 4.1. Intra- and Interoperator Reliabilities. In the present period may have influenced the experiment’s accuracy. The study, intraoperator reliability was good for assessing the ICC value for 0 of cervical flexion may have been superior ° ° upper trapezius at 0 of cervical flexion (ICC = 0 86) and to that of 50 of cervical flexion due to measurement errors. ° ° 50 of cervical flexion (ICC = 0 85), but the interoperator reli- In comparison to keeping the cervical flexion at 0 , maintain- ° ° ° ability at 0 of cervical flexion (ICC = 0 98) and 50 of cervical ing a cervical flexion of 50 according to the Goniometer Pro flexion (ICC = 0 94) was excellent. Our findings were rela- was difficult as holding the cervical flexion at relatively higher tively consistent with those of previous studies evaluating degrees of flexion accurately was difficult, and thus, the error skeletal muscles. SWE was used to assess the upper trapezius of measuring the flexion angles in such cases cannot be with the arm at rest and at 30 ignored. The findings from this study have indicated that of abduction [19]. The intrao- perator (ICC = 0 87) and interoperator (ICC = 0 78) reliabil- the SWE is a credible instrument for evaluating upper ities were good with the arm at rest, corresponding to the trapezius stiffness. SEM < 6 23 kPa and MDC < 17 26 kPa. One study revealed The Bland-Altman plots of our study data further verified the same ICC values (ICC = 0 97) for intra- and interopera- the consistency of our findings. It is clinically acceptable to obtain measurement differences within the limits of agree- tor reliabilities of assessing the upper trapezius using the Myoton PRO with the shoulder in a neutral position [23]. ment [26]. As seen in Figure 3, almost all of the data points One possible reason for the higher ICC values for intraopera- were within the 95% confidence limit. Therefore, the consis- tor reliability than those in our study may be related to the tency of our study data is satisfactory. UT elastic modulus (kPa) UT elastic modulus (kPa) 6 Applied Bionics and Biomechanics stiffness using a Myoton PRO and reported that upper 4.2. Alterations in Upper Trapezius Stiffness during Cervical Flexion. The shear elastic modulus of the upper trapezius trapezius stiffness was significantly reduced by 5.5 N/m after muscle during cervical flexion was quantified using SWE in cervical traction. Furthermore, massage therapy is also a this study. Our results demonstrated that the mean shear good way to relieve pain and tension, as a 19.3% decrease modulus of the upper trapezius at 0 of cervical flexion was in upper trapezius activity was measured by EMG after 40.47 kPa; this value increased to 62.83 kPa at 50 of cervical massage treatment [29]. flexion. Also, the change in the shear modulus was greater The MDC was calculated to detect true changes. In our than the MDC (7.04 kPa), indicating true changes. This is study, the elastic modulus of the upper trapezius should have the first study to examine the effect of different neck positions been greater than 7.04 kPa with different operators to reveal on the elastic modulus of the upper trapezius muscle. It is dif- the true changes with reassessed measurements. ficult to directly compare our findings to those of previous studies. However, previous studies investigated the effect of 4.3. Differences in Upper Trapezius Stiffness between the various shoulder positions on the elastic modulus of the Dominant and Nondominant Sides. Here, we found a signif- upper trapezius muscle. For example, using SWE, Leong icant difference in the elastic modulus of the upper trapezius et al. [19] reported that the elastic modulus of the upper tra- between the dominant and nondominant sides. The high pezius muscle was influenced by shoulder abduction, specify- utilization of the dominant versus the nondominant side ing an increase of 55.23% of shear elastic modulus during may contribute to the long-term usage of the extensor ° ° arm positions of 0 to 30 of abduction. In addition, our muscles, which reasonably explains the differences in stiff- ness. Uthaikhup et al. [30] examined the thickness of the recent study demonstrated that shoulder flexion could affect upper trapezius stiffness using a handheld Myoton PRO lower trapezius and found greater lower trapezius muscle device. We also found a 14.2% increase in upper trapezius thickness on the dominant versus the nondominant side ° ° stiffness at 0 to 60 of shoulder flexion [23]. In addition, of 0 43 ± 0 02 mm. Fatigue of the upper trapezius also dif- using SWE, Maher et al. [27] reported that the elastic fered bilaterally; the upper trapezius on the dominant side modulus of the upper trapezius was affected by a posture was less fatigable by surface EMG [31]. These results were change. Specifically, they reported a 12.2% increase with similar to our findings, which might support the notion of a change from a prone to a sitting position. In another long-term usage of the extensor muscles on the dominant study, an increase in upper trapezius activity was detected side. However, another study reported no significant dif- among smart phone users. The fatigue of the upper trapezius ference in muscle fatigue between the dominant and non- assessed by EMG during cervical flexion revealed a value of dominant sides [11]. The different results might be caused −0 2±1 3Hz at 0 of neck flexion that increased to −3 5± by differences between studies, such as those associated 5 6Hz at 50 of neck flexion [11]. Here, we found an increase with the participant sex, age, and work experience. There- of 35.58% in the elastic modulus of the upper trapezius with a fore, the stiffer upper trapezius on the dominant side ° ° change from 0 to 50 of cervical flexion. might lead to a higher risk of neck and shoulder pain The upper trapezius, as a neck extensor muscle, main- compared to the nondominant side. Our findings could tains cervical spine stability. The external flexion torque be useful in the prevention of neck and shoulder pain, and we should consider the differences in the shear elastic caused by cervical flexion has a significant effect, directly increasing the extensor muscle load. Moreover, muscle over- moduli of the upper trapezius between the dominant and load in a poor posture can easily lead to pathological changes nondominant sides. to the neck and shoulder, while upper trapezius stiffness SWE, a new technique that provides relatively standard can significantly increase among people with neck and elastic parameters of biological tissues, has high accuracy shoulder disorders. For example, using SWE, Leong et al. and sensitivity, features good repeatability, and is a simple [7] demonstrated a 20% stiffer upper trapezius among operative method that measures muscle elasticity from the subjects with rotator cuff tendinopathy compared with that initial qualitative assessment to the quantitative assessment. in healthy subjects. Ishikawa et al. [8] reported an SWE has been widely used in healthy individuals for muscle increased upper trapezius stiffness among people with assessments as well as in biomechanical studies [19, 32, 33]. neck and shoulder complaints compared with healthy sub- Previous comparisons of SWE and a muscle hardness meter jects. Therefore, the 35.58% increase in the shear modulus showed that the former more precisely evaluated neck and of the upper trapezius during cervical flexion noted in our shoulder muscle stiffness [34]. Moreover, assessing alter- study further verifies that poor posture may be a risk ations in supraspinatus stiffness after a margin convergence factor for neck and shoulder complaints. technique using SWE contributed to a deeper insight into Furthermore, recent studies suggested that many thera- the biomechanical effect on the repaired supraspinatus and pies could decrease upper trapezius stiffness. One study provided a scientific and reasonable rehabilitation plan found that dry needling could be used to reduce the elastic [35]. Thus, SWE is expected to be an effective measurement modulus of the upper trapezius, reporting a 12.8% reduction tool for quantitatively evaluating the musculoskeletal system in the elastic modulus of the upper trapezius pre- versus post- under various physiological and pathological conditions. treatment [27]. Cervical traction is a good way to relieve neck discomfort. Sung-Yong and Jung-Hyun [28] examined the 4.4. Limitations. This study had some limitations. First, only influence of three therapies (cervical traction, cranial rhyth- male subjects were included; therefore, sex-based differences mic impulse, and McKenzie exercise) on upper trapezius could not be evaluated. Muscle discomfort caused by a Applied Bionics and Biomechanics 7 [9] U. H. M. Rasim, S. S. Ali, A. Rasheed, and M. Khan, “Fre- computer test was more pronounced in male subjects in a quency and associated risk factors for neck pain among previous study [36]. Further studies of the biomechanical software engineers in Karachi, Pakistan,” Journal of Pakistan characteristics of the upper trapezius of females are required. Medical Students, vol. 67, no. 7, pp. 1009–1012, 2017. Second, we measured only one site of the upper trapezius; [10] P. H. Ko, Y. H. Hwang, and H. W. Liang, “Influence of smart- however, this cannot reflect the entire upper trapezius. It will phone use styles on typing performance and biomechanical be worth exploring the differences in stiffness values in differ- exposure,” Ergonomics, vol. 59, no. 6, pp. 821–828, 2016. ent parts of the upper trapezius in the future. Third, all [11] S. Lee, D. Lee, and J. Park, “Effect of the cervical flexion angle recruited subjects had no neck or shoulder complaints; there- during smart phone use on muscle fatigue of the cervical fore, a subsequent experiment will focus on assessing modu- erector spinae and upper trapezius,” Journal of Physical lations in upper trapezius stiffness using SWE for people who Therapy Science, vol. 27, no. 6, pp. 1847–1849, 2015. suffer from neck and shoulder pain. [12] S. J. Shin, D. H. An, J. S. Oh, and W. G. Yoo, “Changes in pres- sure pain in the upper trapezius muscle, cervical range of 5. Conclusions motion, and the cervical flexion-relaxation ratio after overhead work,” Industrial Health, vol. 50, no. 6, pp. 509–515, 2012. 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Applied Bionics and BiomechanicsHindawi Publishing Corporation

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