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NIU researcher: Prolonged tablet typing may lead to shoulder problems

October 30, 2014
Jay Kim

Jay Kim

Prolonged use of a tablet’s touch-screen keyboard can cause shoulder discomfort. That’s according to a group of researchers, led by Northern Illinois University Assistant Professor Jeong Ho (Jay) Kim, who compared the musculoskeletal impact and typing productivity differences between desktop, notebook and touchscreen keyboards.

The study, published in the November issue of Applied Ergonomics, found that virtual keyboards—which lack tactile feedback mechanisms to indicate a key has been pressed—require less typing force and finger-muscle activity than conventional keyboards. However, because users must keep their fingers hovering to avoid accidentally activating the keys, they risk prolonged static loading in the shoulders.

The researchers recruited 19 experienced virtual-keyboard users who typed passages from Grimm’s Fairy Tales during five-minute typing tests on the three different input devices. The tests were conducted two times on each keyboard, while electrodes recorded muscle activity in the forearms and shoulders and a force platform under the keyboards measured keystroke force.

“When you need to have a greater performance for a longer period of computer interface, then a conventional keyboard would be better, given our finding that performance was about 68 percent better with a conventional keyboard as compared with touchscreen devices,” explains Kim, a faculty member in the NIU Department of Industrial and Systems Engineering.

The average typing speed on a virtual keyboard was found to be 25 words per minute, compared to 63 words on conventional and notebook keyboards, which were also found to be more accurate. Muscle activity in the forearms was lowest when the subjects were typing on a virtual keyboard; however, it was higher in the trapezius muscles in the upper back, which support the shoulders and arms.

Kim says, “When we try to type on a touchscreen keyboard, we cannot rest our fingers on the touchscreen, so we need to extend our fingers to prevent any accidental key activation.”

This floating of hand and forearm while typing likely causes the increased muscle activity in the shoulders when using a tablet. The differences were small but could be important if they accumulate over time, causing shoulder problems, according to Kim.

He says long-term use of a keyboard interface—no matter the type—can cause problems.

Skeleton-Keyboard-400x400“When we type, we need to place our hands to align with all the keys. In order to do that, we need to place our hands on the desk and then squeeze our posture in order to fit to the keys. This causes an ulnar deviation, and also when we place our hands over the keyboards, we create a wrist extension,” Kim says, noting previous research studies have shown that 30 degrees or greater wrist extension significantly increases intercarpal tunnel pressure. “This ulnar deviation has been known to cause inter-carpal tunnel pressure, a risk factor for carpal tunnel syndrome.”

The study was partially funded by Hewlett Packard. With touchscreen smartphones and the increased market share of tablet computers, the use of virtual keyboards is becoming more prevalent. According to a 2014 Pew Internet and American Life Project report, tablet ownership rose from 3 percent in May 2010, to 42 percent in January 2014, among Americans aged 18 and above. Because of this growth, the effects that these keyboards have on a user’s physical exposures, comfort and typing performance become increasingly important to future product design.

“The impact of the use of these touchscreen devices is not only limited to occupational settings, but also for the entire population,” Kim says. “These days, even two-year-old boys or girls are starting to use tablets—their mom’s or dad’s tablets. It is really important for us to understand the potential biomechanical exposures from using these touchscreen devices.”

Kim offers the following tips for reducing the risk of musculoskeletal disorder or discomfort:

  • Find an input device that fits your body by choosing the right-sized keyboard and mouse;
  • Make frequent stops and take breaks when working on a project that involves extensive input; and
  • Use different interfaces so posture can change often.

While he says there is no such thing as a one-size-fits-all paradigm in terms of an optimal computing interface, the type of work being done should influence the type of device to be used.

“If you would like to do simple web browsing or searching for small pieces of information, the touchscreen device is a great tool, because it’s smaller and more portable,” Kim says. “However, if you need to write your papers and work on some projects, then the conventional keyboard computer interfaces would be more suitable.”

Further research will be needed to develop an input mechanism that maximizes performance while reducing extreme postures.

“Our aim as bio mechanists or ergonomists is to reduce awkward posture and promote more neutral posture,” Kim explains.

Ultimately, he says that as alternative interface technology such as voice input improves, physical input devices could be a thing of the past. Other technology that tracks movement of the forearms and digits may also make it possible to interact with a computer without the presence of a physical keyboard.

“Who knows, maybe in the next 10 or 20 years, we may not see the keyboard and mouse anymore. We will just speak to type or we’ll just move our fingers or hands to type without touching anything.”