Effects of typing positions on the upper trapezius and neck extensor muscles electromyography in office employees: A single-blind cross-sectional study

Abstract

BACKGROUND:

Holding incorrect postures over a long period could lead to chronic nonspecific neck pain (CNNP) in office employees.

OBJECTIVE:

The present study aimed to evaluate the effects of different typing positions on the activity of the neck extensor and upper trapezius (UT) muscles of office employees diagnosed with CNNP.

METHODS:

This assessor-blinded cross-sectional study was performed on 22 female subjects with the mean age of 39.95±5.30 years. The neck extensors and UT muscle activities of the participants were assessed in the upright, forward, and slouching postures by electromyography (EMG). In addition, neck proprioception and the performance of the cervical stabilizer muscles were evaluated using an inclinometer and biofeedback pressure unit, respectively.

RESULTS:

A significant difference was observed between the cervical erector spine (CES) and UT muscle activities in the upright, forward, and slouching typing positions (P < 0.05). In addition, a difference was observed between the upright and slouching postures in these muscles. A positive correlation was denoted between CES muscle activity in the slouching and forward postures and the activation index of neck muscles (P < 0.05). Furthermore, a significant, negative correlation was observed between the UT muscle activity in the slouching posture and neck proprioception (P < 0.05). A positive correlation was also noted between the pain index and repositioning error rates (P < 0.05).

CONCLUSION:

CES muscle activity increased in a forward head posture, which could damage neck proprioception through causing early fatigue and stimulating a cumulative damage cycle.

Keywords

Chronic nonspecific neck pain posture neck muscle cervical erector spine

1 Introduction

Chronic nonspecific neck pain (CNNP) is a highly prevalent condition in humans and a common cause of disability among employed individuals. Approximately 67% of adults experience this pain throughout their lives [1]. CNNP is particularly prevalent among office employees due to working with the cervical spine in flexion for long periods [2]. When a person is in the wrong movement pattern for a long time, the antigravity muscle group is stretched and becomes fatigued while holding a forward head posture (FHP) [3]. Long-term holding of an incorrect posture weakens the trapezius muscle and impairs the sensory receptors of gamma motor (motor G) neurons and the reflex of neck muscle regulation [4].

According to the literature, the load received by the cervical spine increases drastically with the increased forward bend angle of the head, which puts office employees at risk of more injuries [5]. The upper trapezius (UT) and lower trapezius muscle activity increase with FHP in order to maintain cervical stability in the new angle, thereby applying huge loads on these muscles [6]. Meanwhile, the control and stability of the cervical spine are impaired by pain [7], and researchers have reported the reduction of isometric power and neck and head muscle endurance in patients with neck pain [8]. In addition, electromyogram (EMG) test results have revealed higher fatigue in the neck muscles of these patients compared to healthy individuals [7, 9]. On the other hand, some researchers have reported neck proprioception impairment in individuals with CNNP compared to healthy individuals [10]. These issues confirm the cumulative cycle of the micro traumas of the cervical spine and the emergence of persistent and chronic neck pain.

Namwongsa evaluated the effects of various neck flexion angles on the neck muscle activity of individuals using smartphones with and without pain. According to the obtained results, the activity of the cervical erector spine (CES) and UT muscles were acceptably low at the neck flexion angle of 0–15 degrees. In addition, the smartphone users with neck pain had slightly higher muscle activity compared to the smartphone users without neck pain [11]. In another study, Østensvika et al. assessed the association between the number of long periods with sustained low-level trapezius muscle activity and neck pain, reporting that low-level trapezius muscle activity in periods longer than eight minutes might be associated with the risk of neck pain [12].

A higher extensor torque is required to handle the increased neck bending torque caused by FHP. If occurring in office employees for a long time as a habitual bad sitting position at a desk, the condition increases the load on the extensor muscles, thereby leading to the higher risk of muscle fatigue. Ultimately, the transfer of the imposed loads to the cervical spine causes a damage cycle, which leads to the persistence of chronic neck pain.

According to the literature, limited activity of the upper trapezius affects the spinal erector muscles, thereby leading to long-lasting neck positions and neck pain [11, 12]. In the present study, the activity of the upper trapezius and spinal erector muscles was evaluated in three neck positions (upright, trunk-forward, and slouching postures). Previous findings have shown neck proprioception defects in individuals with CNNP [10], while the correlation between neck proprioception and different neck positions has not been investigated. In the present study, we assessed the correlation between neck proprioception and different neck positions while typing.

The hypotheses of the present study were as follows: 1) there is a significant difference among office employees with CNNP in the upright, trunk-forward, and slouching postures regarding the activity of the neck extensors and UT muscle and 2) there are correlations between the activity of the cervical extensor and UT muscles in the mentioned positions and factors such as proprioception and performance of the cervical stabilizer muscles.

2 Materials and methods

2.1 Study design

This assessor-blinded cross-sectional study was performed at the Razi University Sports Rehabilitation Laboratory from 22 September 2020 to 20 January 2021. The participants included female office employees with CNNP who worked in similar lighting and temperature conditions and had the same workplace furniture. Cervical extensors and UT muscle activities were assessed in the upright, trunk-forward, and slouching postures. Moreover, the researchers assessed the activity of the mentioned muscles in the three positions considering the neck proprioception and performance of the cervical stabilizer muscles.

2.2 Participants

In total, 22 female employees with chronic neck pain (mean age: 39.95±5.30 years, mean height: 162.25±4.95 cm, mean weight: 71.88±14.88 kg) and a minimum work experience of five years were enrolled in the study. The nonspecific status of the participants’ neck pain was confirmed by a specialist, and the subjects received no therapeutic intervention within six months prior to the study.

Sample size was estimated at 22 subjects using one-way ANOVA based on the study by Namwongsa [11]. The inclusion criteria were as follows: 1) minimum pain intensity score of three (index: 0–10); 2) experiencing neck pain for more than three months; 3) nonspecific neck pain confirmed by a specialist; and 4) dominance of the right hand. The exclusion criteria were as follows: 1) neuropathies/radiculopathies as confirmed by a physician; 2) neuromuscular and/or rheumatoid diseases; 3) history of fractures/dislocations in the hand and neck joints; 4) carpal tunnel syndrome; 5) shoulder impingement; 6) history of upper limb and neck surgery; and 7) vision problems that cannot be corrected with glasses [11, 13]. Written informed consent was obtained from the participants prior to enrolment, and the study protocol was approved by the Ethics Committee of Razi University (code: IR.RAZI.REC.1399.032). Eligible individuals were invited to the Sports Rehabilitation Laboratory of Razi University to undergo the necessary experiments. All participants were called to the laboratory from 10:00 a.m. to 12:00 p.m.

2.3 Outcome measures

We assessed the factors affecting the electromyography (EMG) of the UT and CES muscles, neck proprioception, and performance of the cervical stabilizer muscles.

2.3.1 Muscles’ EMG

The activation of the neck muscles (CES and UT) [14] was measured in three typing postures (each position of text typing was held for 90 s with 2 min rest between each position) using surface EMG. After skin preparation at the right side of the CES and UT to reduce skin impedance, cleaning was performed using 70% alcohol, and the skin was gently abraded using light sandpaper. The surface EMG electrodes were attached 1–2.5 cm apart in parallel with both the cervical erector spine and upper trapezius muscle fibers. The EMG sensors were attached around both C4 areas for the cervical erector spine and slightly outward from the midline between C7 and the acromioclavicular joint for the upper trapezius muscle. The raw EMG of the muscles was recorded at the right side (Noraxon, Scottsdale, AZ 85260, USA) using a pair of Ag-AgCl disposable surface electrodes (diameter: 20 mm; Skintact, Austria). The sampling rate of the EMG signal was set at 1,000 Hz with the signal amplification gain of 1,000 and common mode rejection ratio of 108 dB. The frequency band-pass filter was set at 20–500 Hz, and the location of the surface electrodes was based on the SENIAM recommendations [15]. Maximal voluntary contraction (MVC) was also performed for amplitude normalization [11, 16]. For the EMG normalization procedure, each participant performed three trials of resisted maximum voluntary isometric contraction. Each MVC was performed for five seconds with a two-minute rest interval [17]. Muscle activity was tested in the sitting position for the right UT and CES muscles; the CES muscles were examined with resisted neck extension, and the UT muscles were tested with resisted shoulder elevation.

2.3.2 Neck proprioception

Neck proprioception was measured using a bubble inclinometer (USA). To perform the test, the subjects would sit upright in a chair with back support in a 90-degree knee and pelvis position with the sole of the foot remaining on the ground. The thoracic spine of the subjects was firmly attached to the chair while moving the neck using a strap. To find the target position in measuring proprioception, the examiner considered 50% of the available range of motion of the subject. Afterwards, the subject would stay in two supine and seated positions to measure the proprioception of bending, extending, lateral bending, and rotation. Initially, the range of motion of the neck was measured to determine the target angle, and the head of the subject would be slowly moved toward the target point (50% range of motion) and held at this angle for three seconds. At the next stage, the subject would be asked to remember the angle, so that the head would be returned to its primary position and the subject could move their head to the target point the next time. Finally, the absolute value of the difference between the two angles was recorded as the angle repositioning error. No verbal or visual feedback was provided to the subjects during the test, and the mean value of three measurements was recorded as the repositioning error [18].

2.3.3 Performance of the cervical stabilizer muscles

The performance of the cervical stabilizer muscles was evaluated by the craniocervical flexion test (CCFT). The subjects were positioned in a supine position, lying with both knees bent and the cervical spine in a neutral position. The forehead and chin were aligned horizontally to the plinth surface. The biofeedback pressure unit was placed behind the neck at the suboccipital region and inflated to the baseline pressure of 20 mmHg [12]. Then, the subjects were instructed to perform a slow and controlled craniocervical flexion in a head nod action by progressively increasing the pressure of two mmHg increments (20–30 mmHg) and holding at each increment for 10 seconds. Furthermore, a 30-second rest interval was considered between the successful increments.

During the testing process, the contraction of surface neck flexor muscles was palpated by an assessor whose activity was kept to a minimum. The high activity level of the surface muscles was observed to be an indicator of decreased deep cervical flexor activity. Two types of data were recorded during the CCFT: the activation score (AS) and performance index (PI). The AS was defined as the highest pressure level change achieved by the participants, which could be maintained steadily for 10 seconds. The PI reflected the isometric endurance of the deep cervical flexor muscles, which was calculated by multiplying the number of times the participants could replicate the test at the AS. The highest PI score was set at 100 (10 repetitions at an AS of 10 mmHg) [19].

2.4 Intervention

The participants were asked to re-adjust their desk based on their height and comfort, so that the soles of their feet would be placed on the ground and they could use the footrest, if necessary, considering a 90-degree angle for the knees. The subjects had no back support while typing in the three mentioned postures, and the viewing distance (i.e., space between the operator’s eyes and screen) was set at 70 centimeters. A text typed in a word file was provided to the subjects before the implementation of the typing tests, and they were asked to continuously type the text in three positions of upright, forward, and slouching [20] for 1: 30 seconds (Fig. 1). In addition, two minutes of rest were considered at each posture change, and the activity of the UT and CES was recorded via electromyography in the three postures [17].

Fig. 1

Posture of text typing: a) upright; b) forward; c) slouching.

2.5 Statistical analysis

Data analysis was performed in SPSS version 21.0 (IBM Corp., Armonk, NY, USA) using descriptive statistics to assess the characteristics of the participants. The Shapiro-Wilk test was used to determine the normal distribution of the data; the normally distributed data included age, weight, height, neck pain intensity, neck proprioception, performance of the cervical stabilizer muscles, and UT and CES EMG, and their differences were evaluated using one-way analysis of variance (ANOVA) and Tukey’s post-hoc test. In addition, bivariate correlation was applied to assess the correlations between the EMG of the muscles, performance of the cervical stabilizer muscles, and neck proprioception. In all the statistical analyses, the significance level was set at 0.05.

3 Results

Table 1 shows the general characteristics of the participants. Since this study was conducted only on women, the outcomes cannot be generalized to all populations. Neck pain intensity was measured using the visual analog scale (VAS), which is a standardized, valid, and reliable tool for pain measurement. The visual analogue scale (VAS) in the case group was within the range of 3.00–10.00 centimeters, and the duration of neck pain in these subjects was 3–15 months. In addition, the subjects worked for 3–10 hours per day.

The results of one-way ANOVA showed a significant difference in the CES EMG between the three text typing postures of upright, forward, and slouching (F[2, 65] = 3.17; P = 0.049), as well as a significant difference in the UT EMG between these postures (F[2,65] = 3.42; P = 0.039). Table 2 shows the results of Tukey’s post-hoc test.

Table 1
General characteristics of participants (n = 22)

Variables M SD

Age (year) 39.95 5.30

Weight (kg) 71.88 14.82

Height (cm) 162.23 4.95

VAS (cm) 6.00 2.04

Pain duration (month) 6.13 2.79

Work time (h) 5.77 4.46

Variables	M	SD
Age (year)	39.95	5.30
Weight (kg)	71.88	14.82
Height (cm)	162.23	4.95
VAS (cm)	6.00	2.04
Pain duration (month)	6.13	2.79
Work time (h)	5.77	4.46

M: mean; SD: standard deviation; VAS: visual analog scale; cm: centimeter; h: hours.

Table 2

Comparison of mean CES and UT EMG between text typing positions of participants (n = 22)

Text typing positions
	Variables	Upright/forward	Upright/slouching	Forward/slouching
	CES	9.76±4.42/11.86±4.61	9.76±4.42/13.27±4.90	11.86±4.61/ 13.27±4.90
Muscle EMG	P-value	0.29	0.039^*	0.65
	UT	3.32±1.62/4.23±2.18	3.32±1.62/4.91±2.21	4.23±2.18/4.91±2.21
	P-value	0.30	0.030^*	0.91

Values expressed as mean±SD; EMG: electromyography; UT: upper trapezius; CES: cervical erector spine; P≤0.05.

The results of bivariate correlation indicated that the CES EMG in the slouching posture of text typing was correlated with the activation score of the neck muscles (R = 42%; P = 0.049), and a correlation was also observed between the CES EMG in the forward posture of text typing and the activation score of the neck muscles (R = 42%; P = 0.048). In addition, the UT EMG in the slouching posture of text typing was significantly correlated with neck proprioception (R = –42.8%; P = 0.047), VAS scores (M = –42.8%; SD = 0.047), and neck proprioception (R = 48.7%; P = 0.022) (Fig. 2).

Fig. 2

Scatter/dot plot for correlations between research variables.

4 Discussion

The present study aimed to evaluate the activities of the UT and CES muscles in the office employees diagnosed with CNNP in three typing positions. A significant difference was observed in the CES muscle activity between the upright, forward, and slouching postures. Moreover, a significant difference was denoted in the UT muscle activity between the mentioned positions. Similarly, significant correlations were observed between the muscle activation score and the EMG activity of the UT muscle when typing in forward and slouching postures. Furthermore, a significant relationship was observed between EMG activity of the UT muscle while typing in the slouching position, while pain intensity was also correlated with proprioception. Therefore, it could be concluded that different sitting postures significantly affect the UT and CES muscle activity patterns.

According to the literature, environmental factors such as the couch-sitting position (sitting position on a sofa/couch), furniture position, and accessories used while working (e.g., height of the desk, desk support handle, keyboard, and mouse) affect muscle activity [21 –25]. Some studies have assessed posture differences while using one or two devices in different situations in healthy individuals [26 –28]. While previous research has been focused on the effects of head posture changes while using a laptop on the neck and trunk muscle activity [29], the present study aimed to evaluate the impact of uptight, forward, and slouching postures on the UT and CES muscle activity and determine the correlation between the activity of these muscles with neck proprioception and neck pain in the office employees diagnosed with CNNP. Our findings demonstrated a significant increase in the UT and CES muscle activity due to the forward bending of the head and spine, which supported the hypothesis regarding the increased activity of the cervical extensors and UT muscle with the forward bending of the head for head stability in the new angle, which led to an extreme load imposed on these muscles [6].

According to the results of the present study, the UT muscle activity was relatively low in the forward and slouching postures compared to the upright position, which indicated that the UT muscle was restrained in this position and that its activity was dominant at the end domain of flexion (i.e., forward/slouching). In this regard, our findings supported the hypothesis regarding the significant decrease in the activity of the cervical extensors and UT muscle at an angle of 0–15 degrees [11]. Furthermore, significant correlations were observed between increased muscle activity in the forward/slouching postures, neck pain, and proprioception. This highlights the need for a higher extensor torque in order to handle the increased bending torque caused by the FHP. If occurring in office employees for a long time as a habitual desk sitting position, this condition increases the load on the extensor muscles, thereby leading to a higher risk of muscle fatigue. Ultimately, the transfer of the imposed loads to the cervical spine gives rise to a damage cycle and the persistence of chronic neck pain.

Meanwhile, increased head and trunk flexion have been reported to increase neck pain scores in the long run [30]. For instance, Brink et al. evaluated the association between the sitting posture and sitting-related upper extremity musculoskeletal pain, concluding that increased head and neck flexion over a long period could increase pain scores [30]. Head flexion was also reported to have a predictive potential for upper trunk pain, which is consistent with our findings [31 –33]. In addition, our findings regarding the high activity of the CES muscle in the forward/slouching posture is in line with the results obtained by Caneiro et al. Accordingly, a slump sitting position is associated with increased thoracic flexion, and neck flexion leads to the higher anterior translation of the head [34]. In addition, the results of these kinematic changes are associated with increased CES and UT muscle activity [35]. The increased activity of the CES in the slumped position compared to the forward and upright postures might be due to the fact that the moment arm of the head and neck relative to the axis of rotation located in the cervical vertebra increases due to the higher anterior translation of the head in the slumped sitting position. It seems that the CES activity increases to support the weight of the head and neck in this position.

High muscle activity is likely to cause compressive loads in the cervical-thoracic region in the slump posture through the multi-segmental joints and higher activity of this muscle [35]. Similarly, a slump sitting posture may increase the extension of the upper vertebrae of the neck and the flexion of the lower vertebrae of the neck [36]. Increased head and neck flexion leads to higher activity of the cervical extensors, thereby imposing tremendous stress on the cervical vertebrae and eventually leading to neck pain.

The high activity of the CES and UT in the forward/slouching posture could lead to the fatigue of these muscles and the upper extremities, thereby reducing neck proprioception [32]. In a study conducted by Abdelkader et al., neck muscle fatigue had significant effects on neck proprioception and postural instability [37]. In addition, Vuillerme et al. observed a correlation between muscle fatigue and reduced proprioception [38].

Previous studies have demonstrated that the absence of proprioception due to activation deficiencies in mechanoreceptors may give rise to muscle fatigue. In such cases, fatigue is defined as the inability to produce an expected movement or force [38]. Therefore, neck muscle fatigue, which is caused by the excessive activity of the neck muscles in bending postures, may affect neck proprioception and cause other complications as well.

One of the limitations of the present study was that we could not enroll both male and female subjects.

5 Conclusion

There was a significant difference in the activity of the CES and UT muscles between the upright, forward, and slouching postures. In addition, a difference was observed between the upright and slouching postures in this regard. A positive, significant association was denoted between the CES muscle activity in the forward and slouching postures and the neck muscle activation index. Moreover, a negative, significant correlation was observed between the UT muscle activity in the slouching posture and neck proprioception. Our findings also demonstrated a positive, significant association between the pain index and scores of repositioning error to show the proprioception rate. Therefore, it could be concluded that these head and neck positions affected the excessive activity of the CES and UT muscles, thereby leading to the early fatigue of the muscles. This factor could predict a cumulative damage cycle by affecting neck proprioception. In conclusion, proper training should be provided regarding the maintenance of an upright posture while sitting in order to prevent excessive pressure on the neck in the employees with chronic neck pain. However, the outcomes cannot be generalized to all populations since this study was conducted only on women.

Footnotes

Acknowledgments

The authors extend their gratitude to the office workers for participating in this study and the expert at the Sports Rehabilitation Laboratory for assisting them in this research.

Conflict of interest

The authors have no conflicts of interest to report. The authors confirm that the research presented in this article met the ethical guidelines.

Funding

No funding was used to support this research and/or the preparation of the manuscript.

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