Abstract
The aim of this study was to determine and compare the ergonomic requirements in the use of desktop computers and laptops. For comparison, postures in the sagittal and transversal planes involved while performing a typing and editing task on a desktop and laptop computers were verified. Thus, a case study was conducted with a Brazilian male of medium height, who works around 20 hours per week in a computer. Nine spherical markers of 2.5 cm in diameter were joined up with duct tape on the right side of the participant and the positions adopted by the subject were analyzed in the use of a desktop and a laptop computer, through direct observation and filming, using the videography technique. It is concluded that the use of desktop computers has lesser biomechanical demands since it showed angles closer to a neutral position and consequently having a lower risk of musculoskeletal complaints.
Introduction
The use of the computer is commonly related to the appearance of musculoskeletal complaints [1–6]. Generally, non-neutral postures are considered to be harmful [7]. Gerr et al. [8] state that the postures adopted in the use of the desktop computer are different from those adopted in the use of portable computers.
Portable computers can be used in a variety of postures when not attached to the workstation [7], however, increasing their portability also increases the exposure to potential risk factors for musculoskeletal complaints in relation to desktop computers [9]. The number of laptop users experiencing musculoskeletal disorders has increased drastically due to inappropriate workstations [10]. In particular, since the display and keyboard are connected, the screen height is usually lower than recommended [9, 11].
Images of the subject in the sagittal and frontal plane and the identification of the anatomical reference points, with the respective angles of interest: 1. angle of view, 2. head inclination, 3. neck flexion, 4. craniocervical angle, 5. cervicothoracic angle, 6. shoulder flexion, 7. elbow flexion, 8. wrist flexion-extension, 9. trunk inclination, 10. wrist radial-ulnar.
Laptop computer users reported more postural constraints and higher neck muscle activity than desktop computers. The complaints of ocular and musculoskeletal discomfort as well as difficulty of typing are also greater during the work with portable computers [12]. In comparison to desktop computers, laptop computers results in increased neck flexion and shoulder elevation [4], head inclination [13, 14] and increased neck extension activity [8, 15].
Considering the ergonomics requirements involved in the use of personal computers, the objective of this study was to determine if there are risk factors associated to the evolution of computers, verifying the postures and body angulations involved in the use of desktop computers and laptops.
Study participant
The subject analyzed was a male, 29 years old and works around 20 h per week with a computer, and currently uses a laptop to work. The individual measures 1.70 m in height and has 62 kg, considering that according to Iida [16] the average height of a Brazilian is 1.70 m and the weight is 60 kg, the subject was considered as a median standard. The subject had no musculoskeletal disorders prior to the study.
Experimental protocol
The project in question included the procedures described by the National Health Council under Resolution 196-1996 and ERG-BR 1002 of the Certified Ergonomist’s Code of Ethics in compliance with ethical and scientific requirements. For this purpose, a free and informed consent form (TCLE) was applied, the subject filled out a protocol with basic personal information and another protocol, without identification of the subject, was used to collect the data.
In order to carry out the study, three different situations were considered: (a) use of the desktop computer coupled to the workstation, (b) use of the laptop coupled to the workstation, (c) use of the laptop in an armchair available in the workplace. A desktop computer of LG brand, and a laptop ASUS 546C was used.
The method of approach was documental analysis and direct observation using videography technique. For the videography was used a Nikon L110 camera positioned 1 m of the participant and parallel to the sagittal plane, and a Fujifilm S4200 camera, positioned 0.5 m of the participant and parallel to the transverse plane. The workstation consisted of a 69×170 cm table and an adjustable chair, and the subject was instructed to adjust the chair to a comfortable height. Nine spherical markers of 2.5 cm in diameter were joined up with duct tape on the right side of the participant. To better identify the postural angles, the markers were located in: (1) side margin of the eye; (2) behind the ear; (3) spinous process of C7; (4) acromioclavicular joint; (5) lateral epicondyle of the humerus; (6) ulnar styloid process; (7) head of the fifth metacarpal; (8) midpoint of greater trochanter of the femur (9) computer screen center in the sagittal plane.
From the nine markers and the horizontal and vertical reference lines, the nine postural angles (Fig. 1) were defined as the following, also used by Castellucci and Zúñiga Benitez [11]:
Angle of view: angle formed by the line going from the lateral margin of the eye to the center of the screen, with respect to the horizontal line. The horizontal reference line is designated zero. Below this, the angle value is negative and higher than this, positive. Head inclination: angle formed by the line going from the lateral margin of the eye to behind the ear with respect to the horizontal reference line. Zero is the horizontal line. Below this, the angle value is negative and higher than this, positive. Neck flexion: angle forming by the line going from behind the ear to the spinous process of C7, with respect to the vertical reference line. Zero is the vertical line. Prior to this the angle value is positive and posterior to this, negative. Craniocervical angle: angle formed by the line going from the outer margin of the eye to behind the ear and the line from behind the ear to the spinous process of C7. Cervicothoracic angle: angle formed by the line going from behind the ear to the spinous process of C7 and the line from the spinous process of C7 to the midpoint of the major trochanter of the femur. Shoulder flexion: angle formed along the line from the acromio-clavicular joint to the lateral epicondyle of the humerus, with respect to the vertical reference line. Zero is the vertical line. Prior to this the angle value is positive and posterior to this negative. Elbow flexion: angle formed by the line from the acromio-clavicular joint to the lateral epicondyle of the humerus, and the line of the lateral epicondyle of the humerus to the styloid process of the ulna. The value of this angle is progressively positive and counterclockwise. Wrist flexion-extension: angle formed by the line from the lateral epicondyle of the humerus to the styloid process of the ulna and the line from the styloid process of the ulna to the head of the fifth metacarpal. The first line is called zero. Below this the angle value is negative and higher than this, positive. Trunk inclination: angle formed by the line from the spinous process C7 to the midpoint of the greater trochanter of the femur, with respect to the horizontal reference line. Wrist Radial-ulnar deviation: angle formed by the line from the lateral epicondyle of the humerus to the styloid process of the ulna and the line from the styloid process of the ulna to the head of the fifth metacarpal in the transverse plane. The first line is called zero. Below this the angle value is negative and higher than this, positive.
The work activities of the studied individual, involving typing and text editing, were recorded for approximately 15 minutes, and the intermediate 5 minutes were analyzed. The approaches were conducted inside the working environment during the practice of the activity, in the morning of three different days, before any interaction with the computer that day. For image analysis, the softwares used were Kinovea and Corel Draw while for data collection the software used was Microsoft Excel.
Discussion
The results of the postures assumed during condition N°1 (Desktop use), condition N°2 (Laptop use), and condition N°3 (Laptop use in the armchair) (Fig. 2) can be verified in Table 1. Sixty images of the videos of each condition were analyzed to generate the necessary data for the study of postural angles.
Pictures of the subject in the three different situations analyzed: above, condition No.1 (desktop use), in the middle, condition No.2 (laptop use) and below, condition No.3 (laptop use in the armchair).
Summary of the positions analysis assumed in the three conditions
According to the results obtained, it can be observed that the experimental Condition No. 1, in relation to the other two conditions, presented a lower value in the: angle of view (condition No. 2: difference of 7.31°, condition No. 3: difference of 15.67°), head inclination (condition No. 2: difference of 11.32° and condition No. 3: difference of 30.87°), neck flexion (condition No. 2: difference of 10.37° and condition No. 3: difference of 27.67°), shoulder flexion (condition No. 2: difference of 13.01° and condition No. 3: difference of 15.4°), elbow flexion (condition No. 2: difference of 15.73° and condition No. 3: difference of 36.63°), wrist flexion-extension (condition No. 2: difference of 5.62° and condition No. 3: difference of 20.51°) and wrist radial-ulnar deviation (condition No. 2: difference of 5.83° and condition No. 3: difference of 9.62°). The craniocervical and cervicothoracic angles were higher in the experimental condition No. 1 (Craniocervical angle: condition No. 2: difference of 10.02° and condition No. 3: difference of 12.13°; cervicothoracic angle: condition No. 2: difference of 13.04° and condition No. 3: difference of 17.87°) while the trunk inclination was greater in condition No. 2 (condition No. 1: difference of 11.85° and condition No. 3: difference of 15.78°).
These values demonstrate that the Condition No. 1 performed with a desktop computer, compared to other conditions, translates into a more upright posture of the head and neck and a more neutral posture of the shoulders, elbows and wrists. It is also noted that the Condition No. 2, performed with a laptop on a work table, presented values closer to a neutral posture compared to the Condition No. 3, performed with a laptop in an armchair, in all postural angles except the craniocervical angle, the cervicothoracic angle and the trunk inclination.
The results found in this study were similar to those obtained in other studies [11], demonstrating that the most impacting factors on postural angles between the use of a desktop computer and a laptop are the height of the computer screen and use of external components (keyboard and mouse). Castellucci and Zúñiga Benitez [11] obtained the following values for angle of view, head inclination, neck flexion, craniocervical angle, cervicothoracic angle, shoulder flexion, elbow flexion, wrist flexion-extension and the trunk inclination, respectively: –40,3°; –4.64°; 61.42°; 147.13°; 113.44°; 20.87°; 94.66°; –11.59°; 94.23° in an experiment with laptop coupled to a workstation, obtaining better results using the laptop with external components as keyboard and mouse.
In this study, we obtained –9.57° for head inclination in the use of the laptop and 1.75° in the use of the desktop computer, similar to other studies that obtained the values –9.8° for head inclination in the use of the laptop and 1.75° in the use of the desktop computer [13], also 57.4° for neck flexion in the laptop and 50° in the desktop computer, while we obtained 57,79° and 47,42°, respectively. A study with laptops obtained –12.7° for wrist flexion-extension [1], and another study [3] found –12.79° for wrist flexion-extension and 39.52° for shoulder flexion, compared to –13.74° and 37.79° obtained in this case study.
Regarding the values found for angle of view, the normal line of sight is between 10 and 15° below the horizontal line [17]. This normal line of sight is the resting position of the eyes, and it is recommended that the objects to be viewed are at this limit. Also, in the posture seated with the trunk erect, people prefer to visualize objects at 20° below the horizontal line [16]. In this study, in all conditions, the angle of view exceeds 20° below the horizon line, however, in the case of the desktop computer, it exceeds only 1.18°, and for the laptop this value is higher, surpassing in around 8° in condition No.2 and 16° in condition No.3.
The neck flexion should be up to 20° [16]. Above 30° the pain in the neck begins to appear. Again, in all conditions the value exceeds the ideal, and in condition No. 1 the value is around 20° above the recommended, but in condition No. 2 and No. 3 this value exceeds the recommended in 33° and 51° respectively. The recommended trunk inclination is between 90° and 120° [16] and all conditions are within the recommended value.
A wrist ulnar deviation greater than 20° is significantly associated with musculoskeletal injuries [8]. In the case of the desktop computer (condition No. 1), the ulnar deviation of the wrist is 18.52°, however in the case of the laptop, the ulnar deviation is greater than 20° in both condition No. 2 (24.35°) and condition No. 3 (28.14°), being condition No. 3 the most problematic.
Even using the same working configuration, there are divergent values between the use of the laptop and the desktop computer, where the desktop computers requires less biomechanical demands since it showed angles closer to a neutral position, and consequently having a lower risk of musculoskeletal complaints.
The objective of this study was to determine and compare the ergonomic differences in the use of desktop computers and laptops, verifying the sagittal and transverse plane postures involved during the execution of a typing and editing task in each equipment. The analysis of the average postural angles assumed during the execution of tasks with a desktop computer demonstrated a more upright posture of the head and neck and a more neutral posture of the shoulders, elbows and wrist compared to the postural results during the use of the laptop. The obtained values are similar to the researched literature, evidencing that the use of the laptop in comparison to the desktop represents a greater risk of musculoskeletal complaints. Thus, it is concluded that although laptops allow greater mobility, they would not be adequate for periods of continuous use, and in this case the use of desktop computers is indicated. This study analyzed the postures in the laptop without considering external components such as mouse and keyboard, therefore, it is recommended as future studies the postural analysis in laptops with the help of external components, to verify the influence of the display of laptops in assuming less neutral postures.
Conflict of interest
None to report.