Tom Cruise is hardly out of shape. After all, he’s been running in movies since 1981. But according to some reports, he had to frequently rest his arms while shooting the Minority Report Pre-Crime scenes. This condition is often called gorilla arm – when your muscles feel sore and stiff after holding out your arm for extended periods of time. So how can we avoid gorilla arm and still feel awesome?
Thinking about ergonomic design
Ergonomics is a challenge in the field of motion control. As designers and developers, our goal should always be to empower the user, and not make them feel tired or inadequate. The Minority Report interface fails the reality test on three counts: it forces users to (1) wave their hands and arms around (2) at shoulder level (3) for extended periods of time. That would wear anyone out.
At Leap Motion, we’ve developed ergonomics guidelines to help make using the Leap Motion Controller feel natural and easy. At the end of this article, I’ve included the full guidelines from our information guide (PDF). But first, some tips for developers!
People get tired when they have to perform an interaction repeatedly for a long time. As Dan Saffer points out in Why you want (but won’t like) a Minority Report-style interface, context is important:
“There are situations where large-scale, broad gesture gestural interfaces make sense: gaming, collaboration situations, public installations, possibly industrial settings. In general: activities that are short-term in duration.”
In general, brief interactions are much easier on users, such as in casual gaming or media applications.
Taking a break
Of course, some activities intrinsically take up lengthier interaction times, such as flying around Google Earth or sculpting clay in Freeform. Because the sensor is always on, it’s important to create a null mode for apps that require lengthy interactions. For instance, when flying around Google Earth, the user can make a fist and withdraw their hand without impacting the app controls.
Some Airspace apps pause the game automatically when no hands are detected – also good practice. Users should be able to drop their hands from the interaction space without causing unintended consequences.
Relaxed shoulders and elbows near torso
When standing or sitting and using the computer, it’s good to keep your elbows near the torso and your shoulders relaxed, as in sketches below. Design your app with this posture in mind.
Anticipating user stances and poses
Some stances and poses will naturally use more energy and may cause discomfort over time. Try this quick exercise: relax your hands completely. This is the zombie hand pose, which is probably the most comfortable. Now make the “hang loose” sign. Do you feel the exertion in your fingers and forearms?
The “hang loose” sign.
Certain hand poses are much more comfortable than others. Very uncomfortable poses shouldn’t be held for more than a few seconds. Through user testing, we’ve found that new Leap Motion users often get so excited that they elevate their entire arm in non-ergonomic ways. As an app developer, here’s how you can help them stay in a comfortable posture:
- Remind new users to keep their elbows at their sides.
- Tweak the angles when you program with hand variables, so that the most ideal hand positions work with lowered elbows.
- Assuming your app is for desktop users, pick a comfortable interaction height that can be reached with the elbow down.
Always keep your user’s comfort in mind and evaluate your app from the perspective of hand, arm and shoulder fatigue. If it’s a utility app, consider frequency of use and make interactions ridiculously fast and easy to access (e.g. switching tools in Freeform). It’s OK for less frequently accessed interactions to take longer or more energy.
User testing is also key. Watch the user play out your entire game level, or watch them spend 10 minutes on a utility task. Monitor your user’s fatigue and comfort level. All in all, user testing with realistic tasks is the best way to uncover hidden problems in a user experience.
Appendix: Ergonomics for Users
You can find the latest version of these ergonomics guidelines on our website.
When using your Leap Motion Controller, locate it so that it is comfortable to use. Center your controller in front of your keyboard or laptop. Adjust your chair or work surface so that your elbows are near your side and your forearms are roughly parallel to the floor. Your chair may need to be slightly higher or your work surface slightly lower than usual.
You should sit at such a height so that your forearms extend at roughly a right angle from your body to a position slightly above your Leap Motion Controller, with your wrist and hands in roughly a straight line. Your hands should be just above the device, and your shoulders should be relaxed.
You can also rest your forearms or elbows on the work surface, but do not rest on a sharp edge.
If you have discomfort, take a break, and when using the controller again, change your arm posture. If you have persistent or recurrent discomfort after use, stop use and see a physician.