This article is reprinted with permission from The Ergonomics Report™ Archives, where it originally appeared on February 22, 2012.
A recent study by the Harvard School of Public Health and Microsoft Corporation looked at the head and neck postures typical of tablet computer users. Tablet computers with touchscreen displays such as the iPad are becoming increasingly common with Apple selling some 45 million iPads in 2011 –taking approximately 15% of the total PC market. Tablet computers are expected to continue growing in popularity with projections for them to grow to 300 million units per year and taking 60% of the total PC market by 2015, therefore understanding the ergonomics associated with these portable computers is a concern for ergonomists.
Back to the future:
Because the input and display are integrated into one unit, the postures and biomechanics of touchscreen computers are closer to working with pen and paper than with a desktop computer. The desktop computer, and even the laptop computer, provide separate input and output interfaces (keyboard separate from display). Having separate keyboard, mouse and display generally allows a more upright posture of the head and neck as compared to tablet computer use. The human-computer-interaction for touchscreen tablet computers is different than for the traditional desktop computer.
The authors of this study note: “posture guidelines for traditional computing have been addressed by ergonomics and MSD standards such as the ISO-9241, ANSI/HFES 100, DSE Regulations and others. However the newer technology devices have not been adequately represented in these standards. Therefore this study is an important step in identifying and quantifying the postural demands of tablet computer use.”
Because computer work has been and continues to be associated with discomfort and pain in the neck and shoulders. Many studies have investigated how display/ monitor positioning affects neck and shoulder posture and muscle activity. Higher displays lead to decreased head and neck flexion that approaches neutral postures; lower gaze angles lead to increased neck extensor muscle activity. Excessive head flexion leads to large muscle loads and strains. Therefore, it is generally hypothesized that very low monitors may increase the risk of neck and shoulder discomfort or MSDs.
This research aims to study the head and neck postures for various user configurations commonly observed during typical tablet computer use and how neck and head posture varies with different tablets and their case designs with different tilt angle settings.
Subjects: 15 tablet computer users were fitted with 3-dimensional kinematic instruments that accurately measured various head, neck, and visual parameters while the subjects performed a series of computing, gaming, and media tasks. All of the test subjects were adults experienced in the use of tablet computers.
Test Conditions: All of the tablet tasks were performed while seated in a lounge-style chair with no armrests and a reclined back angle. The seat height was 44 cm/ 17” high, and subjects also had an ottoman-style footrest (40 cm/ 15” high) that could be used if desired. The third piece of furniture was a small table to be used for the media-viewing task.
Two media tablet computers were used; an Apple iPad2 and a Motorola Xoom (Both were similar in size, with the iPad measuring 241 X 185 X 9 mm/ 9.5 X 7.25 X .35 inch and mass of 601 g/ 1.3 lbs. and the Xoom being slightly smaller and heavier).
Each device was tested in the landscape orientation.
Each table utilized a proprietary case that could be fitted to the device and adjusted to prop up or tilt the tablet computer. The Apple case allowed for tilt angles of 15 and 73 degrees. The Motorola case allows for tilt angles of 45 and 63 degrees.
Four user conditions were analyzed. These included
|Cofiguration||Location of tablet||Tablet support/ basis of tilt||Software task performed|
|Lap-Hand||Subject's lap||One or both hands/ self-selected tilt||Internet browsing, reading, game playing|
|Lap-Case||Subject's lap||Case/ lower case tilt setting||Internet browsing, reading. Email reading & responding.|
|Table-Case||Table surface||Case/ lower case tilt setting||Internet browsing, reading. Email reading & responding.|
|Table-Case||Table surface||Case/ upper case tilt setting||Movie watching.|
The researchers measured various head and neck postures including:
- Head & neck flexion (forward bending from vertical)
- Crania-cervical angle (angle ABC where; A. C7 Vertebra, B. Ear Canal, and C. Corner of Eye)
- Visual Gaze Angle (angle from horizon to eye to center of tablet screen)
Results and Conclusions (from the study):
- The use of tablet computers is associated with high head and neck flexion postures, especially compared to the postures observed in typical desktop or even laptop computer scenarios.
- Overall, for both tablets, Head and neck flexion was quite large and 15 – 25 degrees beyond "neutral" head and neck posture when working with the tablet in the lap and when hand-held.
- The postures observed are affected by the type of case used to support the device, as well as the location of the device (e.g. lap vs table). For example, the iPad case had a lower tilt and resulted in more neck and head flexion as compared to the Xoom case.
- The results suggest that head and neck posture can be improved through case designs that allow for optimal viewing angles and by elevating the device and avoiding lap-level locations.
What this means for the ergonomics practitioner:
When providing ergonomic advice for tablet computer users we need to consider how the device is used, we need to consider the "work" environment, and we need to take a systems approach to ensure that we don't optimize for one function and cause problems in another area.
Tablet computers can be used to consume content such as when reading or viewing a video, and they can be used to create content such as when inputting text or other media. Consuming and creating each place different demands on the user and may require different placement configurations depending on the duration, frequency, and importance of the task.
If the device is used primarily to consume media such as viewing video or reading web pages, then we want to optimize position for viewing. This means:
- Place the device higher than the lap (raise it up with a pillow, book or other object)
- Tilt the screen toward the eyes
- Place the device at an appropriate viewing distance to avoid forward bending.
- If the device must be hand-held, consider an armrest or pillow under the arm to prevent arm and shoulder fatigue.
If the device is primarily being used to create or input content, then we need to balance the positioning to accommodate the visual system and the hand/wrist/ arm.
- Placing the device flat on the desk is great for the hand/ arm but will result in neck flexion.
- Tilting the device up can help reach a balance between the two systems. However, placing the device up on a sharp angle may result in wrist extension and strain. In this instance we need to think of the tablet more as a writing pad, and consider the benefits of positioning the device on a gentle up slope much like the artist or engineer did when using a drafting table.
- For intensive inputting (keying), consider using an external keyboard that links with Bluetooth connections.
Justin Young, Matthieu Trudeau, Dan Odell, KIm Marinelli, and Jack Dennerlein, "Touch-screen tablet user configurations and case-supported tilt affect head and neck flexion angles," Work: A Journal of Prevention, Assessment and Rehabilitation, Volume 41, Number 1, 2012.
About the reviewer: Gene Kay MS, CEA is a work physiologist and a BCPE Certified Ergonomics Associate. He is a former Global Ergonomics Manager, a former Rehab Services Manager, the Past President of the Upper Midwest HFES, and is the owner and developer of the ErgoAdvocate on-line training program.
This article originally appeared in The Ergonomics Report™ on 2012-02-09.