EFFECT OF DIFFERENT HOLDING DEVICES ON THE USER S BODY POSTURE WHILE OPERATING TABLET COMPUTER

Transcription

1 EFFECT OF DIFFERENT HOLDING DEVICES ON THE USER S BODY POSTURE WHILE OPERATING TABLET COMPUTER Suebsak Nanthavanij, Thanpicha Ditthaprasert, Phattranit Jittiarunchai, Jutamat Chutigraiwun, and Athippong Prasertsukdee School of Management Technology Sirindhorn International Institute of Technology, Thammasat University Pathum Thani 12121, THAILAND , suebsak@siit.tu.ac.th Abstract This paper reports an investigation on the effect of three holding devices on the user s body posture while operating a tablet computer. Specifically, the three tablet computer holders are: (1) mobile holder (MH), (2) table-top holder (TH), and (3) swing-arm holder (SH). An experiment was conducted to observe body postures of a group of university students when they were required to operate a tablet computer at a given workstation. Four trials were performed in the experiment. In the first trial, the tablet computer was placed freely by the subject on the work surface. For the remaining three trials, the three holders were used alternately to hold the tablet computer during its use. The distance and angle were also adjusted for appropriate viewing and operation. A rapid upper limb analysis (RULA) technique was applied to evaluate the user s neck, trunk, upper arm, lower arm, and wrist postures of the users. It is found that all three tablet computer holders are equally effective in helping the subjects to assume the ergonomic work posture. Keywords: Tablet computer, Holding device, Work posture, RULA 1. INTRODUCTION Over the past years, tablet computers have become widely popularly among people in different age groups. Young people (in elementary, junior high school, and senior high school) use them for their education and entertainment. Teenagers and university students tend to use tablet computers for their non-voice communications such as Internet browsing, social networking, and entertainment. Working people use tablet computers for both their work and leisure activities. The elderly, especially those who are technologically inclined, also use tablet computers, but mostly for reading e-books/e-magazines, digital news, etc. Tablet computers were firstly introduced as an alternative to smart phones and notebook computers to improve the user experience for certain tasks such as browsing the web, reading/writing s, and playing video games (Trudeau et al., 2013). Owing to their mobility, ease of use, and low cost (compared to desktop and notebook personal computers), tablet computers (or tablets, for short) are being used for accomplishing the same tasks as computers (Müller, 2012). As the result of popularity growth in tablet computers, sales of personal computer have been falling. One reason contributing to the sharp decline in personal computer sales was a change in preferences in consumers wants and needs. Corresponding author 253

2 It is known that prolonged computer work especially with awkward work posture is a leading cause of discomfort and pain in the neck and shoulder among computer users. Several researchers have investigated how display/monitor positioning affects neck and shoulder posture and muscle activity. Higher display location leads to decreased head and neck flexion and helps to approach the neutral neck posture; while lower gazes lead to increasingly flexed postures which are associated with an increase in neck extensor activity (Straker et al., 2006). A biomechanical model of the neck musculature shows that excessive head flexion leads to large muscle loads and strains (Young et al., 2011). The sudden popularity and adoption of the tablet computer has not allowed for typical physical ergonomics parameters such as posture or muscular effort during use to be sufficiently assessed. Although the keyboard peripheral is not required for the general operation of the tablet computer, the soft (or on-screen) keyboard is present for accomplishing the typing activity. For common tasks such as web browsing, communications, and social networking, the soft keyboard remains a necessary and frequently used component for facilitating the user-tablet computer interaction. Using the tablet computer for extended period of time has raised concern about musculoskeletal discomfort especially if the work posture is inappropriate. With respect to the effect on the head and neck postures, the position of the center of the tablet s screen relative to the eyes (gaze angle and gaze distance) becomes an important issue (Sommerich et al., 2007). The combination of repetitive movements, poor posture, and overuse of tablet computer without taking rest breaks can cause injury to the nerves, muscles, and tendons in the fingers, hands, wrists, arms, elbows, shoulders, and neck, which, if ignored, may lead to long-term damage. Readers should note that the risk factors associated with prolonged and improper use of tablet computer and its adverse effects on body parts are similar to those related to both desktop computer and notebook computer uses. This research study is intended to investigate the effect of three tablet computer holders on the postures of the upper extremities and trunk of the user. These tablet computer holders are: (1) mobile holder (MH), table-top holder (TH), and swing-arm holder (SH). The postures of neck, upper arm, lower arm, wrist, and trunk are investigated using the rapid upper limb assessment (RULA) technique. In the paper, the experiment and its results are described. The comparison of body postures with respect to different tablet computer holders is also discussed. 2. COMMON POSTURES DURING THE USE OF TABLET COMPUTER The tablet computer is a mobile electronic device. Although it has some features which are different from the notebook computer, they still shares several commonalities such as mobility, wi-fi Internet connectivity, information processing, and battery-powered operation. As such, tablet computer users tend to use their devices in various places both indoor and outdoor. Figure 1 shows the photos of university students using their tablet computers in different places around the university campus. 254

3 Figure 1: Common body postures during the use of tablet computers Readers should note that although tablet computers are used at different places, most users are found to bend the neck excessively to view the screen. From Figure 1, the first user holds the tablet computer in her hands so that she can view the screen more conveniently. While her neck posture seems to be natural, her shoulder flexion is excessive and it is likely that she will develop fatigue and discomfort on her upper arms. The last user places her upper arms on the table while using her tablet computer. This action causes both trunk flexion and shoulder abduction. These photos are only some examples of the body postures commonly seen on tablet computer users. 3. EXPERIMENT An experiment was conducted to observe how different tablet computer holders affect the body posture of the user. This section briefly describes the equipment, subjects, and test procedure of the experiment. 3.1 Equipment Tablet Computer The tablet computer used in this experiment is an ipad Tablet Computer Holders Three tablet computer holders were tested in this experiment. The first holding device is a mobile tablet computer holder (MH). It consists of two pieces. The first piece is a back cover that has to be attached to the tablet computer. The second piece is a base unit that has to be inserted into the back cover. It is foldable and its base angle can be adjusted to achieve a proper screen angle. In addition, the tablet computer can be placed for either portrait or landscape view. The second holding device is a table-top tablet computer holder (TH). It also consists of two pieces. The first piece is the same back cover that is used with the mobile holder. The second piece is a base unit that is set on the table. It can be adjusted to hold the tablet computer at two levels: low and high. Similar to the mobile holder, the tablet computer can 255

4 be set for either portrait or landscape view. The third holding device is a swing-arm tablet computer holder (SH). Its 2-piece arm is clamped at the top surface of the table. There are three joints that enable the adjustments of the tablet computer position and angle. The first joint is at the base of the swing arm, the second joint is the one between the proximal and distal sections of the arm, and the third joint is between the distal section and the holding plate. Figure 2 shows the photos of three tablet computer holders just described above. (a) MH (b) TH (c) SH Figure 2: (a) Mobile, (b) table-top, and (c) swing-arm tablet computer holders 3.2 Subjects Ten university students, five males and five females, voluntarily participated in this experiment without receiving any monetary compensation. The subjects were explained about the objective and procedure of the experiment prior to their participation. All subjects are experienced tablet computer users, with three subjects having one year of experience, one subject having two years of experience, five subjects having three years of experience, and one subject having more than three years of experience. Table 1 summarizes the subjects biographical data. 3.3 Test Procedure Initially, the subject was interviewed to obtain his/her biographical data and information about the use of tablet computer. The subject was then seated at the table and was instructed to place the given tablet computer (i.e., ipad 2) on the table according to his/her preference. Note that the subject was not allowed to hold the ipad 2 on his/her hands. Furthermore, a smart cover which can be folded to adjust the screen angle was not used in the experiment. The subject was also advised to adjust the seat height of the adjustable chair to suit his/her body height. While using the ipad 2, the subject s snapshot side-view photo was taken from the side corresponding to the subject s preferred hand. 256

5 Table 1: Biographical data of ten subjects Subject Gender Age Body Height Average Use Time per Day Preferred Hand (year) (cm) (hour) S1 Male Right 1 S2 Female Right 2 S3 Male Left 2 S4 Female Right 3 S5 Male Right 3 S6 Female Left 6 S7 Male Right 2 S8 Female Right 2 S9 Male Right 2 S10 Female Right > 4 Next, the above mentioned holding devices were tested one at a time to hold the tablet computer at the table. They were used according to the following order: mobile holder, table-top holder, and swing-arm holder. With the holding device, the position and angle of tablet computer were adjusted to facilitate the viewing and typing activities. The subject was then instructed to use the tablet computer while his/her body posture was observed and recorded. Note that the subject was not allowed to change the settings of the tablet computer during the operation. For each holding device, the use of tablet computer was not longer than ten minutes. No official rest breaks were provided. A re-setup of the holding device took less than five minutes, during which the subject was relaxing at the workstation. The same procedure was applied to all ten subjects. A rapid upper limb analysis (RULA) technique was applied to evaluate the neck, trunk, upper arm, lower arm, and wrist postures of the subjects. RULA is a quick and simple technique for evaluating the body posture. From a snapshot photograph of the body posture, one body part is focused at a time. For any body part, its posture is compared to several given postures. The posture that is the closest to the subject s posture is chosen and its corresponding score is used to represent the RULA score of that body part. It should be noted that the natural posture has the RULA score of 1. The further the posture is deviated from the natural posture, the greater the RULA score becomes. 4. RESULTS Figure 3 shows the body postures of subject S7 who is a male subject with average body height (according to the Thai population). The body postures when the ipad 2 was placed directly on the table and when the three tablet computer holders were used are displayed 257

6 together for comparison. Dash lines connecting relevant body joints are also shown to help detecting the awkward postures of various body parts. (a) No holder (b) MH (c) TH (d) SH Figure 3: Body postures of subject S7 during tablet computer use When subject S7 was using the ipad 2 without any tablet computer holder, his body posture was very awkward especially at his neck, trunk, and lower arm. Readers can easily see that all three tablet computer holders can help to adjust the viewing angle of ipad 2. Consequently, his body posture becomes more natural in those three body parts during the tablet computer use. Note that the MH holder was adjusted to hold the ipad 2 at its low level since this subject is only average in terms of body height. Comparing the neck, trunk, upper arm, lower arm, and wrist postures of this subject among the three table computer holders, it is seen that the MH, TH, and SH holders are equally effective in helping to adjust the height and angle of the ipad 2 such that the subject can view and operate the tablet compute with more natural body postures. Table 2 presents the RULA scores of the neck, trunk, upper arm, lower arm, and wrist postures of subject S7. Table 2: RULA scores of subject S7 s body postures Tablet Computer Holder Body Part Neck Trunk Upper Arm Lower Arm Wrist No Holder Mobile Table-top Swing-arm The RULA scores of five body part postures under four work conditions, namely, no holder, mobile holder, table-top holder, and swing-arm holder, are presented in Table 3. For individual body parts, the scores are averaged from ten subjects. The numbers shown in 258

7 parentheses are the standard deviations. When no tablet computer holder is used, the subjects had poor postures in all five body parts. The neck seems to be affected the most when placing the tablet computer directly on the table. Excessive neck flexion was a common posture among most subjects especially the tall male subjects. Several subjects also leaned their trunk forward during the viewing and typing on the soft keyboard. For short female subjects, they tended to place their arms on the table while operating the soft keyboard. This shoulder abduction also increased the RULA score of the upper arm posture. For those who did not place their arms on the table, they were likely to flex both the lower arm and wrist in order to operate the soft keyboard. All three tablet computer holders are equally effective in helping to adjust tablet computer angle and, consequently, the postures of the neck, trunk, upper arm, and lower arm. However, wrist flexion was still seen in a number of subjects. This could be due to the attempt to set the angle of tablet computer for appropriate viewing, which might have caused the wrist to still flex while operating the soft keyboard. Table 3: Average RULA scores of five body part postures Tablet Computer Holder Neck Trunk Upper Arm Lower Arm Wrist No Holder (0.82) (0.63) (1.03) (0.48) (0.52) Mobile Holder (MH) (0.67) (0.00) (0.32) (0.48) (0.52) Table-top Holder (TH) (0.42) (0.00) (0.00) (0.42) (0.48) Swing-arm Holder (SH) (0.42) (0.00 (0.32) (0.42) (0.48) Note: The numbers in parentheses are standard deviations. 5. CONCLUSION The postures of the neck, trunk, upper arm, lower arm, and wrist are observed during the use of tablet computer. Four settings of tablet computer on the table are studied. For the first setting, the tablet computer is placed directly on the table. For the remaining three settings, the tablet computer is held by the mobile holder, table-top holder, and swing-arm holder. An experiment is conducted to investigate the effectiveness of tablet computer holders in helping to adjust the screen angle of the tablet computer to improve the neck, trunk, upper arm, lower arm, and wrist postures. The results from ten subjects show that placing the tablet computer directly on the table causes awkward neck, trunk, upper arm, lower arm, and wrist postures. The use of tablet computer holder can help to adjust the screen angle 259

8 which, consequently, improve the neck, trunk, upper arm, and lower arm postures. All three types of tablet computer holders are found to be equally effective based on the decreased RULA scores of the above mentioned five body part postures. ACKNOWLEDGMENTS The authors would like to express their appreciation to Sirindhorn International Institute of Technology, Thammasat University, for providing financial support for this research study. REFERENCES Müller, H., Gove, L. J., and Webb, S. J. (2012) Understanding tablet use: a multi-method exploration, Proceedings of the 14th ACM International Conference on Human-Computer Interaction with Mobile Devices and Services, San Francisco, CA; United States. Sommerich, M. C., Ward, R., Sikdar, K., Payne, J., and Herman, L. (2007) A survey of high school students with ubiquitous access to tablet PCs, Ergonomics, 50(5), Straker, L., Burgess-Limerick, R., Pollock, C., Murray, K., Netto, K., Coleman, J., and Skoss, R. (2008) The impact of computer display height and desk design on muscle activity during information technology work by young adults, Journal of Electromyography and Kinesiology, 18(4), Trudeau, B. M., Catalano, J. P., Jindrich, L. D., and Dennerlein, T. J. (2013) Tablet keyboard configuration affects performance, discomfort and task difficulty for thumb typing in a two-handed grip, PloS ONE, 8(6). 260