Musculoskeletal disorders and functional characteristics of the neck and shoulder: Comparison between office workers using a laptop or desktop computer

Abstract

BACKGROUND:

Using a laptop for work is gaining rapid popularity, but there is little evidence of how it influences musculoskeletal disorders (MSDs) and functional characteristics of the neck and shoulder area.

OBJECTIVE:

This study aimed to compare the prevalence of upper body MSDs and functional characteristics of the neck between office workers using a laptop or desktop computer.

METHODS:

A total of 110 office workers with a mean age of 41±10 years participated. 45 office workers (73% female) used a laptop and 65 office workers (86% female) used desktop computers. The prevalence of MSDs was recorded using the Nordic Musculoskeletal Questionnaire. Active range of motion (AROM), maximal voluntary isometric contraction (MVC) force, joint position error (JPE), and pain-pressure threshold (PPT) of the neck and shoulder area were measured.

RESULTS:

Laptop users experienced significantly more MSDs in the right shoulder area on the day of participation (p < 0.001, OR = 4.47), during the previous 7 days (p < 0.01, OR = 3.74), and at 6 months (p < 0.01, OR = 3.57). Laptop users also experienced significantly more MSDs in the left shoulder during the previous 7 days (p < 0.05, OR = 2.44). There were no statistically significant differences in any of the functional characteristics of the neck and shoulder area between the groups.

CONCLUSION:

Using the laptop computer for office work may pose a higher risk of developing MSDs in the right shoulder area, but might not have long-term effects on the functional characteristics of the neck and shoulder area.

Keywords

Musculoskeletal pain range of motion muscle strength proprioception nociception

1 Introduction

Laptop computers are gaining popularity in several areas including office work and education. The main reasons behind the increasing usage of laptops are portability, low weight, affordable prices, wireless access, and connectivity. For these reasons, the advantages of laptop computers outweigh desktop computers in most categories [1]. Since laptops are also used for leisure purposes, and with the recent increase in working or studying from home, the trend towards using more laptops instead of traditional desktop computers is believed to continue [2].

Musculoskeletal disorders (MSDs) are a common problem among office workers, causing decreased work ability, increased sick leave, and long-term disability [3]. MSDs among office workers are complex issues influenced by individual and work-related risk factors. Individual risk factors include higher age, female gender, poor overall health, and lifestyle factors, such as low physical activity [4 –7]. Work-related risk factors include awkward postures, static load, poor ergonomic conditions, and low physical activity during the workday [4 , 8]. Several authors have discussed ergonomic concerns in laptop users, such as difficulty keeping a neutral posture, not using optimal ergonomics, and adjustability restrictions due to its specific design [9 , 12]. In contrast to previously stated ergonomic concerns, working with a laptop can provide more variability in posture and locations of work due to its portability. Thus, postural variability and variance of work environment might have a positive impact on work-time physical activity and reduction of MSDs [13]. The most common types of MSDs among laptop users are shoulder pain, neck pain, lower back pain, wrist pain, and finger pain [14]. The prevalence of MSDs in these body regions is similar to the results of studies investigating the prevalence of MSDs among office workers without addressing which type of equipment was used for work [15, 16]. In this study, we investigated the prevalence of MSDs separately, depending on the type of computer used, to better determine if any difference is present.

A laptop computer can be used in different positions and configurations. Studies have investigated discomfort and muscle activity in different body positions and laptop configurations. When changing the position of work or the physical configuration of the laptop, muscle activity and discomfort seem to shift to different areas, making it impossible to find the best posture and setting to use the laptop [9, 17]. Laptop users have been shown to work in more extreme postures than desktop computer users. The most common difference in posture is increased flexion of the neck, which can potentially cause postural strain to the musculoskeletal system in the neck and back [18]. Postural strain is considered one of the factors leading to MSDs [10]. There is some evidence that postural changes in the neck, particularly forward-head posture, are associated with changes in functional characteristics, such as lower maximal voluntary isometric contraction (MVC) force of neck extensor muscles [19], and reduced range of flexion in the neck [20]. It is also known that neck pain alone is associated with changes in functional characteristics, such as reduced neck active range of motion (AROM) [21], MVC force [22], joint position error (JPE) [23], and pain-pressure threshold (PPT) in certain neck and shoulder areas [24]. The differences in neck posture between laptop and desktop computer users have been recorded [25], however, the differences in such functional characteristics of the neck are little studied. Previous research has investigated primarily the short-term effect of laptop use on certain functional characteristics of the neck and shoulder area [26]. The long-term effect of using a laptop-type computer on the functional characteristics of the neck and shoulder area, investigating possible musculoskeletal adaptation, is little studied.

The aim of this study was to compare the prevalence of upper body MSDs and functional characteristics of the neck and shoulder area among office workers using a laptop or desktop computer for work. More specifically, AROM, MVC force, JPE, and PPT were measured as functional characteristics. Because laptop usage can cause more awkward postures [9 , 11], which are associated with a higher postural strain resulting in MSDs [10] and negative changes in functional characteristics of the neck [19, 20], we hypothesized that laptop users have more neck and shoulder area MSDs and impairments of functional characteristics of the neck and shoulder area when compared with workers using a desktop computer.

2 Materials and methods

2.1 Subjects

A total of 110 office workers (80.9% female) with an age range of 23–60 years (mean 40.97±9.96 years) participated in this study. Based on the type of computer used for work, the subjects were divided into two groups: laptop users (n = 45) and desktop computer users (n = 65) as a control group. The work-related data, demographic information, and physical activity are presented in Table 1. There were no statistically significant differences between the groups based on this data. The inclusion criteria included working in an office setting, working with a computer for at least six hours a day, and age between 20–60 years. The inclusion criteria for the laptop group included using a laptop-type computer for work without an external display, keyboard, or mouse. The exclusion criteria were chronic neurological, orthopedic, metabolic, or inflammatory conditions, legally designated disability, and a body mass index (BMI) over 30 kg/m². The participants were recruited from five different organizations by contacting their health and safety officer. The organizations operated in the fields of telecommunication, energy, health, and education. The inclusion criteria for the organizations entailed using modern and recently updated work equipment. All participants had contemporary furniture including an adjustable office chair and an electronically or manually adjustable desk. The participating organizations used modern ergonomic guidelines enforced by certified occupational health specialists. The guidelines were developed by the occupational health service providers for the participating organizations. The participating organizations implemented a standard 8-hour workday with a 30-minute lunch. Besides the lunch break, all participants had an opportunity to take smaller breaks on demand. Participation in this study was voluntary and all the participants signed the informed consent form. This study was approved by the Ethics Review Committee on Human Research, University of Tartu. (Report nr 287/T-26). The comparison of demographic and work-related characteristics between the groups is presented in Table 1.

Table 1
Demographic and work-related characteristics of the subjects based on the type of computer used for\\ work (mean±SD)

Feature Desktop users Laptop users p-value

(n = 65) (n = 45) (95% CI)

Age (years) 41.78±9.99 39.89±10.11 0.346 (–1.977 to 5.768)

Female (%) 86.2% 73.3% 0.09

BMI (kg/m²) 24.30±3.25 23.98±3.43 0.627 (–0.966 to 1.624)

Right handed (%) 97.1% 93.3% 0.37

Work experience (years) 16.04±9.97 15.16±10.74 0.561 (–3.137 to 4.901)

EICS (years) 8.05±8.45 5.79±7.55 0.109 (–0.790 to 5.310)

BPAI score 8.12±1.38 7.72±1.47 0.155 (–0.153 to 0.950)

BPAI work score 1.95±0.31 2.00±0.35 0.460 (–0.173 to 0.086)

Screen time at work (hrs) 7.74±1.16 7.72±1.75 0.880 (–0.579 to 0.612)

Feature	Desktop users	Laptop users	p-value
Age (years)	41.78±9.99	39.89±10.11	0.346 (–1.977 to 5.768)
Female (%)	86.2%	73.3%	0.09
BMI (kg/m²)	24.30±3.25	23.98±3.43	0.627 (–0.966 to 1.624)
Right handed (%)	97.1%	93.3%	0.37
Work experience (years)	16.04±9.97	15.16±10.74	0.561 (–3.137 to 4.901)
EICS (years)	8.05±8.45	5.79±7.55	0.109 (–0.790 to 5.310)
BPAI score	8.12±1.38	7.72±1.47	0.155 (–0.153 to 0.950)
BPAI work score	1.95±0.31	2.00±0.35	0.460 (–0.173 to 0.086)
Screen time at work (hrs)	7.74±1.16	7.72±1.75	0.880 (–0.579 to 0.612)

BMI – body mass index; EICS – experience in current settings; BPAI – baecke physical activity index.

2.2 Study design

The study took place at the participants’ workplace in a private room adjusted for this study. The data collection consisted of two parts. First, filling the questionnaires for determining eligibility for participation and assessing the prevalence of MSDs. The second part consisted of measuring height, body weight, AROM and JPE of the neck, MVC force of the neck muscles, and soft tissue PPT of the neck and shoulder region.

Self-reported physical activity, body mass index, and physical demands of the work were measured to assess the homogeneity regarding lifestyle and physical work demands, of the two groups. Baecke Physical Activity Questionnaire was used to measure the self-reported overall physical activity and work-related physical activity.

Order of procedures:

The research methods were introduced to the participants, and informed consent was signed.

The suitability for this study was assessed using the Pre-Test questionnaire.

Body height and weight were measured, and BMI was calculated.

Subjects filled in the Baecke Physical Activity Questionnaire, and the Nordic Musculoskeletal Questionnaire.

AROM of the neck was measured.

JPE of the neck was measured.

MVC force of the neck muscles was measured.

PPT of the soft tissues in the neck and shoulder region was measured.

2.3 Evaluation of MSD prevalence

The Modified Nordic Musculoskeletal Questionnaire was used to determine the prevalence and duration of MSDs in different body regions. Exclusion of data regarding lower-limb MSDs was deemed necessary since its association with this type of computer work evidenced low correlation to upper extremities. Thus, this data was less relevant regarding the scope of the study. The duration of MSDs was recorded as current pain, pain in the previous 7 days, and pain in the previous 6 months.

2.4 Measurements of functional characteristics

To gather data about the adaptation of the musculoskeletal system, the functional characteristics were measured during rest. The measurements were implemented during the mid-day lunch hours. All of the functional characteristics were measured on the same day. During the measurements of functional characteristics of the neck and shoulder region, the subject was sitting on an adjustable piano bench, with 90 degrees of flexion in the hip and knee joints, and feet fully supported on the ground. The participants were asked to keep their natural posture and support their forearms on their thighs.

The AROM of the neck was measured using a CROM goniometer (Performance Attainment Associates, USA). Flexion, extension, lateral flexion, and rotation for both sides were measured. The reading was recorded when the participants reached the maximum possible active range of motion, perceived pain, or began to compensate with their trunks. The unit of measurement used was degrees of rotation (°). Every function was measured three times and the arithmetical mean was calculated.

The JPE was measured using a laser-pointer mounted to the midline on the CROM goniometer. The JPE target was attached to the wall at eye level approximately 90 cm in front of the subject. The unit of measurement for JPE was millimeters (mm). The participants were asked to point the laser in the middle of the target, close their eyes, rotate the head to the side as far as possible, and return to the middle without opening their eyes. The final point was measured from the center of the target. JPE was measured six times on both sides and the arithmetical mean for each side was calculated.

The MVC force of the neck muscles was measured using a hand-held digital dynamometer Lafayette Manual Muscle Testing System (Lafayette Instrument Company, USA). The positions of measurement were adapted from a protocol in previous research [27]. The MVC force was measured in protraction, extension, and lateral flexion to the left and right. The unit of measurement for MVC force was kilograms (kg). The participants were asked not to compensate with their trunk or limbs by keeping them in place and using only the neck. Depending on the direction measured, the dynamometer was held by the researcher against the participant’s forehead, temporal region, or occipital region. The participants were asked to hold their heads in a neutral position and push against the dynamometer to build up to their maximal cervical muscle force over three seconds while maintaining the static neck position. During the procedure, the researcher applied counter-force to prevent the dynamometer from moving. Every direction was measured three times, with 60 seconds of rest between the repetitions. The maximum value was used in statistical analysis.

The PPT of the subjects was measured using a handheld digital algometer with a rubber disk area of 1 cm² and provided a quantitative measurement of sensory perception of mechanical stimuli. To assess the PPT, the rubber disk of the algometer was applied perpendicularly against the skin on the test area, and the pressure was applied at the rate of approximately 50 kPa/s. The PPT was defined as the pressure (kPa) where the pain was first experienced. The subjects were instructed to push a button, when they reached the PPT, locking the exact value on the display of the algometer. We included three test sites on both body sides. The first site was the midpoint of the upper trapezius, measured from the spinous process of C7 to acromion. The second site was the inferior end of the levator scapulae muscle near the superior angle of the scapula. The third point of measurement was the midpoint of neck extensor muscles, measured from the base of the neck to the base of the skull. The assessment consisted of three sets of measurements 5 minutes apart. The mean PPT was included in the statistical analysis. All measurements were carried out by a licensed physiotherapist.

2.5 Statistical analysis

The prevalence of MSDs is presented as percentages. To determine the statistically significant differences in the prevalence of MSDs between the groups, Fisher’s exact test was used. Odds ratios with 95% confidence intervals were used to express the magnitude of the difference among statistically significant results. The functional characteristics of the groups are presented as mean±SD. Normality was determined using the Shapiro-Wilks test with the significance level set to p < 0.05. Depending on the distribution, the Welch t-test or Mann-Whitney U test was used to determine the statistical significance when comparing the means of functional characteristics between the groups. 95% confidence intervals were included in the comparison of functional characteristics. Data analysis for MVC force and PPT was done separately for both genders. Multivariate logistic regression analysis was used to find associations between neck and shoulder pain as the dependent variable, type of computer used for work, and functional characteristics of the neck and shoulder region as independent variables, correcting for age, gender, BMI, screentime, and physical activity. For the regression analysis, total AROM, total MVC force, total JPE, and total PPT were used, where the results of directions/locations of individual characteristics were merged. This merged model was used to reduce correlations between covariates for a better fit. The results of this analysis are presented as odds ratios and 95% confidence intervals. RStudio version 3.6.3 was used for the statistical analysis.

3 Results

Table 2 represents the prevalence of MSDs in different body areas among office workers working with a laptop or desktop computer. The results indicate a higher prevalence of neck and shoulder region MSDs among workers using a laptop when compared with the control group. The difference was significant particularly in the right shoulder area, whereas the overall neck and shoulder MSD prevalence was slightly higher among laptop users, but did not reach statistical significance. Laptop users demonstrated a significantly higher prevalence of right shoulder pain on the day of participation (p = 0.048, OR = 4.41, 95% CI 0.98 to 27.40), in the previous 7 days (p = 0.012, OR = 3.69, 95% CI 1.24 to 12.03), and the previous 6 months (p = 0.003, OR = 3.53, 95% CI 1.49 to 8.63), when compared with desktop computer users. Laptop users also had a significantly higher prevalence of left shoulder pain in the previous 7 days (p = 0.049, OR = 2.42, 95% CI 0.93 to 6.45) when compared with desktop computer users.

Table 2
Prevalence of musculoskeletal disorders among office workers working with a laptop (n = 45) or desktop (n = 65) computer

Body area 1 day 7 days 6 months

Laptop N (%) Desktop N (%) OR (95% CI) p Laptop N (%) Desktop N (%) OR (95% CI) p Laptop N (%) Desktop N (%) OR (95% CI) p

NS 17 (37.8) 18 (27.7) 1.58 (0.65 to 3.74) 0.302 28 (62.2) 33 (50.8) 1.59 (0.69 to 3.74) 0.249 40 (88.9) 51 (78.5) 2.18 (0.67 to 8.40) 0.203

Neck 14 (31.1) 12 (18.5) 1.98 (0.74 to 5.36) 0.171 20 (44.4) 26 (40.0) 1.20 (0.52 to 2.77) 0.697 33 (73.3) 43 (66.2) 1.40 (0.57 to 3.59) 0.530

Left shoulder 5 (11.1) 6 (9.2) 1.23 (0.28 to 5.20) 0.757 16 (35.6) 12 (18.5) 2.42 (0.93 to 6.45) 0.049 21 (46.7) 22 (33.8) 1.70 (0.73 to 4.00) 0.233

Right shoulder 8 (17.8) 3 (4.6) 4.41 (0.98 to 27.40) 0.048 14 (31.1) 7 (10.8) 3.69 (1.24 to 12.03) 0.012 26 (57.8) 18 (27.7) 3.53 (1.49 to 8.63) 0.003

Lower back 7 (15.6) 9 (13.8) 1.14 (0.33 to 3.80) 0.791 15 (33.3) 25 (38.5) 0.80 (0.33 to 1.90) 0.688 26 (57.8) 49 (75.4) 0.45 (0.18 to 1.10) 0.062

Upper back 5 (11.1) 8 (12.3) 0.89 (0.21 to 3.36) 1.000 15 (33.3) 19 (29.2) 1.21 (0.49 to 2.96) 0.679 25 (55.6) 40 (61.5) 0.78 (0.34 to 1.82) 0.559

Left elbow 0 (0.0) 1 (1.5) 0.00 (0.00 to 56.28) 1.000 1 (2.2) 4 (6.2) 0.35 (0.01 to 3.69) 0.647 4 (8.9) 6 (13.3) 0.96 (0.19 to 4.34) 1.000

Right elbow 4 (8.9) 2 (3.1) 3.04 (0.41 to 35.06) 0.224 4 (8.9) 5 (7.7) 1.17 (0.22 to 5.80) 1.000 11 (24.4) 11 (16.9) 1.58 (0.55 to 4.52) 0.344

Left WHF 1 (2.2) 2 (3.1) 0.72 (0.01 to 14.19) 1.000 3 (6.7) 3 (4.6) 1.47 (0.19 to 11.52) 0.687 10 (22.2) 11 (16.9) 1.40 (0.48 to 4.07) 0.623

Right WHF 4 (8.9) 6 (9.2) 0.96 (0.19 to 4.34) 1.000 7 (15.6) 11 (16.7) 0.91 (0.27 to 2.83) 1.000 13 (28.9) 17 (26.2) 1.15 (0.45 to 2.90) 0.829

Body area	1 day	7 days	6 months
NS	17 (37.8)	18 (27.7)	1.58 (0.65 to 3.74)	0.302	28 (62.2)	33 (50.8)	1.59 (0.69 to 3.74)	0.249	40 (88.9)	51 (78.5)	2.18 (0.67 to 8.40)	0.203
Neck	14 (31.1)	12 (18.5)	1.98 (0.74 to 5.36)	0.171	20 (44.4)	26 (40.0)	1.20 (0.52 to 2.77)	0.697	33 (73.3)	43 (66.2)	1.40 (0.57 to 3.59)	0.530
Left shoulder	5 (11.1)	6 (9.2)	1.23 (0.28 to 5.20)	0.757	16 (35.6)	12 (18.5)	2.42 (0.93 to 6.45)	0.049	21 (46.7)	22 (33.8)	1.70 (0.73 to 4.00)	0.233
Right shoulder	8 (17.8)	3 (4.6)	4.41 (0.98 to 27.40)	0.048	14 (31.1)	7 (10.8)	3.69 (1.24 to 12.03)	0.012	26 (57.8)	18 (27.7)	3.53 (1.49 to 8.63)	0.003
Lower back	7 (15.6)	9 (13.8)	1.14 (0.33 to 3.80)	0.791	15 (33.3)	25 (38.5)	0.80 (0.33 to 1.90)	0.688	26 (57.8)	49 (75.4)	0.45 (0.18 to 1.10)	0.062
Upper back	5 (11.1)	8 (12.3)	0.89 (0.21 to 3.36)	1.000	15 (33.3)	19 (29.2)	1.21 (0.49 to 2.96)	0.679	25 (55.6)	40 (61.5)	0.78 (0.34 to 1.82)	0.559
Left elbow	0 (0.0)	1 (1.5)	0.00 (0.00 to 56.28)	1.000	1 (2.2)	4 (6.2)	0.35 (0.01 to 3.69)	0.647	4 (8.9)	6 (13.3)	0.96 (0.19 to 4.34)	1.000
Right elbow	4 (8.9)	2 (3.1)	3.04 (0.41 to 35.06)	0.224	4 (8.9)	5 (7.7)	1.17 (0.22 to 5.80)	1.000	11 (24.4)	11 (16.9)	1.58 (0.55 to 4.52)	0.344
Left WHF	1 (2.2)	2 (3.1)	0.72 (0.01 to 14.19)	1.000	3 (6.7)	3 (4.6)	1.47 (0.19 to 11.52)	0.687	10 (22.2)	11 (16.9)	1.40 (0.48 to 4.07)	0.623
Right WHF	4 (8.9)	6 (9.2)	0.96 (0.19 to 4.34)	1.000	7 (15.6)	11 (16.7)	0.91 (0.27 to 2.83)	1.000	13 (28.9)	17 (26.2)	1.15 (0.45 to 2.90)	0.829

NS – neck & shoulder; WHF – wrist, hand and fingers. Statistically significant results (p < 0.05) are presented in bold.

Our analysis of the functional characteristics of the neck and shoulder area indicated no statistically significant differences between the groups. We found no statistically significant differences in AROM of the neck, nor in neck JPE between laptop and desktop computer users (Table 3). There were no statistically significant differences in MVC force of the neck muscles when laptop users were compared with desktop computer users of the same gender (Table 4). Laptop users did not present any statistically significant differences in the PPT of the muscles in the neck and shoulder area when compared with desktop computer users of the same gender (Table 5).

Table 3

Active range of motion and joint position error of the neck in desktop users and laptop users (mean±SD)

Function	Desktop users	Laptop users	p-value	95% CI
	(n = 65)	(n = 45)
Flexion (°)	57.30±9.43	56.58±10.38	0.71	–3.13 to 4.57
Extension (°)	70.15±14.58	72.81±11.13	0.28	–7.52 to 2.21
Left LF (°)	50.07±10.26	52.12±10.16	0.30	–5.97 to 1.88
Right LF (°)	46.04±10.35	46.55±10.72	0.80	–4.58 to 3.56
Left rotation (°)	68.67±9.31	70.92±9.26	0.27	–5.82 to 1.32
Right rotation (°)	68.19±8.55	70.20±9.91	0.27	–5.63 to 1.60
Left rotation JPE (°)	51.67±20.79	46.61±13.30	0.30	–1.39 to 11.51
Right rotation JPE (°)	53.08±14.59	49.64±14.88	0.25	–2.25 to 9.11

LF – lateral flexion; JPE – joint position error.

Table 4

Maximal voluntary contraction force of the neck muscles in office workers based on\\ the type of computer used for work (mean±SD)

Function	Desktop users (n = 65, 86% females)	Laptop users (n = 45, 73% females)	p-value	95% CI
Protraction (kg)
Female	8.46±8.76	7.61±2.14	0.6	–1.60 to 3.30
Male	11.44±4.29	11.49±3.38	0.98	–3.74 to 3.65
Extension (kg)
Female	9.02±2.77	9.59±2.74	0.34	–1.76 to 0.62
Male	10.84±3.67	12.97±2.83	0.17	–5.27 to 1.02
Left LF (kg)
Female	6.55±1.77	6.95±2.10	0.62	–1.26 to 0.47
Male	9.60±3.26	10.38±3.06	0.59	–3.73 to 2.18
Right LF (kg)
Female	6.23±1.89	6.81±1.94	0.23	–1.42 to 0.26
Male	8.89±2.76	10.33±3.52	0.31	–4.32 to 1.43

LF – lateral flexion.

Table 5

Pain-pressure threshold of different neck and shoulder regions among office workers\\ based on the type of computer used for work (mean±SD)

Location	Desktop users (n = 65, 86% females)	Laptop users (n = 43, 72% females)	p-value	95% CI
Left UT (kg)
Female	6.99±2.61	6.99±3.40	0.68	–1.41 to 1.42
Male	8.86±6.35	6.37±2.62	0.72	–2.52 to 7.48
Right UT (kg)
Female	6.90±2.56	6.68±3.94	0.25	–1.37 to 1.80
Male	8.79±7.28	6.94±2.32	0.97	–3.82 to 7.53
Left LS (kg)
Female	8.62±3.72	8.05±3.63	0.44	–1.06 to 2.21
Male	9.79±8.16	7.86±4.55	0.97	–4.67 to 8.53
Right LS (kg)
Female	8.25±3.68	8.13±3.40	0.94	–1.44 to 1.69
Male	8.81±7.42	7.52±4.22	0.81	–4.73 to 7.30
Left NE (kg)
Female	3.77±1.70	3.75±1.39	0.76	–0.65 to 0.94
Male	3.38±2.61	3.15±1.83	0.81	–1.95 to 2.43
Right NE (kg)
Female	3.64±1.61	3.76±1.55	0.69	–0.83 to 0.58
Male	3.37±2.39	3.33±1.91	0.91	–2.03 to 2.11

UT – upper trapezius; LS – levator scapulae; NE – neck extensors.

Table 6 shows the results of the binary logistic regression analysis, investigating the associations between neck and shoulder pain, using a laptop for work, and functional characteristics of the neck. The model was corrected for age, sex, BMI, screen time, and physical activity. The models presented a good fit with the area under the ROC curve (AUC) of 0.67–0.73. The analysis suggested significant associations between acute neck and shoulder pain and AROM of the neck, however, the odds ratios were indicating an irrelevant effect size for these associations.

Table 6

Multivariate logistic regression model for neck and shoulder pain with different duration in office workers (n = 108, 80.6% females)

Factor	NSP at the moment		NSP in previous 7 days		NSP in previous 6 months
	OR	95% CI	OR	95% CI	OR	95% CI
Laptop	2.25	0.86 to 6.44	1.54	0.65 to 3.74	2.14	0.64 to 8.24
Total neck ROM	0.98	0.97 to 0.99	0.99	0.98 to 1.00	0.99	0.98 to 1.00
Total neck Fmax	1.01	0.97 to 1.06	1.01	0.97 to 1.06	0.96	0.91 to 1.02
Total neck JPE	1.00	0.98 to 1.01	1.00	0.99 to 1.02	1.02	0.99 to 1.04
Total neck PPT	0.97	0.94 to 1.00	1.00	0.98 to 1.03	1.03	0.99 to 1.08

Statistically significant results (p < 0.05) are presented in bold. NSP – neck and shoulder pain; ROM – range of motion; Fmax – maximal voluntary contraction force; JPE – joint position error; PPT – pain pressure threshold.

4 Discussion

The main findings of this study were:

Laptop users had a significantly higher prevalence of MSDs in the right shoulder area.

The functional characteristics of the neck did not differ significantly between laptop and desktop computer users.

In this study, we measured the prevalence of MSDs in the upper body and spine regions. The overall prevalence of MSDs in both groups was high with 98% of subjects in both groups experiencing MSDs in the upper body and spine during the previous 6 months. In the previous 7 days, 80% of laptop users and 78% of desktop computer users had experienced MSDs in any body region. These general results indicate that the type of computer used for work does not determine the overall prevalence of MSDs and other factors must be considered.

Considering that the position of the computer screen is an integral difference between laptops and desktops resulting in different degrees of neck flexion [28], we hypothesized a higher prevalence of MSDs in the neck and shoulder region among laptop users. In the neck and shoulder region, we recorded MSDs in the neck, left, and right shoulder and calculated the total prevalence of neck and shoulder MSDs. In the Nordic Musculoskeletal Questionnaire, the neck region was visualized from the base of the skull down to the C6-C7 height. The lateral part of the upper trapezius muscle was counted as the shoulder area. Despite the laptop group having a higher prevalence of MSDs in the neck area, the difference was not statistically significant. Previous research has indicated the weekly prevalence of neck pain among laptop users is over 70% [29]; however, in our subjects, the weekly prevalence was only 44.4% and the 70% prevalence was reached when the previous 6 months were addressed. The difference between the studies can be explained by a different questionnaire since our study inquired about pain, not including slight discomfort. The statistically significantly higher prevalence of MSDs in the shoulders can be explained by a higher postural strain on the upper trapezius muscles caused by the forward head posture [30]. In addition to the forward head posture, using a laptop without an external keyboard or mouse can also cause awkward upper limb positions, such as elevated shoulders, therefore causing additional muscle activity in the upper trapezius muscles [31]. Using a laptop without an external mouse might cause prolonged shoulder elevation, particularly on the side of the dominant hand, which can explain the significantly higher right shoulder MSD prevalence in our sample, which was 93.3% right-handed. Considering this mechanism, our result of higher shoulder pain prevalence in the laptop group is supported by previous research, indicating prolonged upper trapezius activity as an associated factor in developing neck and shoulder pain [32]. When either neck or shoulder MSDs was considered as an indicator of the overall neck and shoulder area MSDs, the total prevalence was not statistically significant during the day of participation (p = 0.363, 95% CI –0.11 to 0.33), the past 7 days (p = 0.321, 95% CI –0.09 to 0.31), or the past 6 months (p = 0.244, 95% CI –0.08 to 0.43). Our finding of higher shoulder MSD occurrence is similar to previous research which suggested that the shoulder area, especially the right shoulder, is the primary site of musculoskeletal strain among laptop users [32].

This study found no significant differences in MSD prevalence in other body areas besides the shoulders. The long-term prevalence of MSDs in other body areas was similar to previous research which did not differentiate between the type of computer used [5]. Minor differences were present in the prevalence of lower back pain during the previous 6 months, with desktop computer users experiencing additional lower back pain (75% vs 57%). However, because the difference did not achieve statistical significance (p = 0.062), further studies with a higher sample size are needed to investigate this possible difference. Considering previous research, presumably using a laptop might increase postural variety, reduce static postures, and reduce the overall chance of developing lower back pain compared with desktop computer usage [13]. In both groups, the overall prevalence of lower back pain was high and comparable with research on the prevalence of MSDs among office workers, indicating a prevalence of over 50% [5, 15].

There were no statistically significant differences between the desktop and laptop groups when the functional characteristics of the neck and shoulder area were compared. The AROM of the neck did not differ between the desktop and laptop groups. This indicates that different neck posture from using a laptop is not a relevant factor for causing changes that might limit AROM. Since the neck position during work differs between desktop and laptop computer users, we measured the MVC force of the neck muscles to see how it affects the neck muscles’ ability to generate force. From our data, it is concluded that the type of computer used for work does not influence the force generation ability of the neck muscles. This finding is supported by previous research, suggesting that forward head posture is not associated with altered muscle performance, pain, or disability [35]. Similarly, regression analysis results indicated no association between neck and shoulder pain and total isometric strength of the neck muscles (Table 6). The neck muscles’ ability to generate force can be disturbed by the prevalence of chronic neck pain [36], but the laptop group did not experience more neck pain. On the contrary, the pain was more prevalent in the shoulder region, therefore not compromising the neck’s ability to generate force. While it is known that JPE is altered in subjects experiencing pain [22], our result of no differences in neck JPE between the groups can indicate that the position is not altered by the type of neck posture used for work, since the prevalence of neck pain was similar in both groups. Previous research has indicated that laptop users might have a better joint position in the neck when compared with dual monitor users, but strong conclusions cannot be made due to the small sample size used (n = 27) [26]. Because there were significantly more MSDs in the shoulder areas among laptop users, the neck JPE test could be used with lateral flexion instead of rotation to induce more discomfort in the upper trapezius region while executing the test. Using lateral flexion might include more shoulder region influence on the outcomes of the test. We measured PPT as an indicator of pressure sensitivity of soft tissues in the neck and shoulder area. Working with a laptop in a seated position with increased neck flexion can cause more static muscle activity in the neck extensors and shoulder muscles [17], which can cause lowered PPT as a symptom of soft tissue overload [37]. Since the prevalence of acute shoulder area pain was higher among laptop users, we expected to find differences in the PPT in the upper trapezius region. There were no statistically significant differences in any of the locations measured between laptop and desktop computer users. We believe this is due to most workers feeling neck and shoulder region discomfort during screen usage, which will be alleviated during breaks or leisure. Since there were differences in the prevalence of MSDs and no differences in the functional characteristics measured, our results suggest that the effect on the musculoskeletal system is more subjective when working with a laptop computer. This study can provide practical insight for specialists working in occupational health to better understand the effect of different types of computers used for work on the subjective and objective characteristics of the musculoskeletal system. The results can be used by physiotherapists and other occupational health specialists when assessing the worker and explaining work-related nonspecific neck pain. Due to the multifactorial complexity of MSDs, focusing on biomechanics alone is not sufficient and intervention methods should be based on the biopsychosocial model of pain.

The novelty of this study lies in using multiple tools for the measurement of possible MSD-related characteristics. MSDs are complex issues; therefore, we believe multiple methods are necessary for better understanding, including both subjective and objective methods used in this study. The strength of this study is also the sample size of over 100 participants, which is more than most original research studies measuring functional characteristics [22 , 24]. This study has several limitations. One of the main limitations of this type of study is exposure control. It is almost certain that the selected type of computer used for work is also used for other purposes. Also, different types of computers or smart devices might be used outside of work. All participants had been introduced to contemporary ergonomic guidelines and had the opportunity to use an adjustable office chair and desk, however considering the portability of laptop computers and the design of this study, we are not aware of how much work was done in different settings, especially in the laptop group. In non-laboratory settings, this kind of exposure control is almost impossible to implement, therefore the results must be interpreted with caution. The gender ratio of the groups was slightly different, which could have influenced the results of MSD prevalence since the female gender is considered a risk factor in developing some MSDs [5 , 34]. We analyzed the Fmax and the PPT separately for male and female participants, but the number of male participants was too low to draw any conclusions from that data. When comparing the prevalence of MSDs, there were several body regions that came close to reaching statistical significance. The prevalence of MSDs in this study was recorded as a subjective outcome to compare with objective measurements, therefore the prevalence outcomes should be interpreted cautiously. Future studies comparing the prevalence of MSDs between laptop and desktop computer users should include higher sample sizes for more statistical power. Another limitation is not including questions about in which setting the participants used the laptop because as a portable device, it can be used in many different settings and postures. Despite having investigated self-reported work-related physical activity, we do not have data on how many breaks workers took or how often they moved. Future studies should investigate work-related physical activity between the users of different types of computers by using a more objective method, such as accelerometry. We measured the functional characteristics of the neck but did not focus on the shoulder area. Since laptop users had a significantly higher prevalence of MSDs in the shoulder region, future studies investigating the functional characteristics should include the shoulder joint. For a better understanding of changes related to the type of computer used for work, we also recommend future research to monitor the functional characteristics, pain, and discomfort continually throughout the workday and recovery. Recording the amount of exposure to different places of work and settings should be recorded in future studies investigating the effect of using a laptop on MSDs. Due to the complexity of MSDs, other factors, such as properties of the furniture, individual knowledge of ergonomics, behavioral factors, and psychosocial factors, must be considered when interpreting the results.

5 Conclusion

Office workers using a laptop for work had a significantly higher prevalence of MSDs in the right shoulder area when compared with office workers using a desktop computer for work. The prevalence of MSDs in the neck area or the total prevalence of neck and shoulder MSDs did not differ significantly between the groups. Workers using a desktop computer had a tendency towards a higher prevalence of MSDs in the lower back during the previous 6 months when compared with workers using the laptop computer. There were no differences in the AROM, MVC force, JPE, or PPT of the neck and shoulder area regarding office workers using a laptop or desktop computer for work. According to our data and previous research, using a laptop for work might cause more MSDs in the neck and shoulder area; however, it might not have a long-term effect on the functional characteristics of the neck and shoulder area. For a better understanding of the impact of using a laptop for work, further studies should investigate the use of laptops continually through the work process and recovery.

Ethical approval

This study was approved by the Ethics Review Committee on Human Research, University of Tartu (Report nr 287/T-26).

Informed consent

Participation in this study was voluntary. Informed consent was obtained from all participants.

Conflict of interest

The authors declare that they have no conflict of interest.

Footnotes

Acknowledgments

The authors would like to thank all participants for contributing their time and data.

Funding

This research received no specific funding from any funding agency in the public, commercial, or not-for-profit sectors.

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