Biomechanical simulations show how cell phones stress muscles

Computer scientists have developed a procedure that simulates in a lifelike manner which muscles and joints are put under particular strain when using a computer or a cell phone.
The method, developed by scientists from Saarland University in Germany and colleagues, uses cameras to capture the motion of a test subject and then projects these movements onto a model of the human body.
Tense shoulders, neck strain or a painful wrist are not uncommon among those who spend long periods of time working at a computer.
This sort of problem can also arise when using the newer types of IT devices that have appeared on the market over the last few years, researchers said.

For example, the use of gestures to control games consoles can cause particularly high levels of stress to shoulders or knees.
Touch screens that require users to hold their arm in an extended position for long periods of time can also be problematic - experts refer to this specific type of muscle fatigue as 'gorilla arm'.

To help designers and developers of new IT devices take into account those movements that create unnecessary bodily strain, graduate researcher Myroslav Bachynskyi and his colleagues have developed a tool that enables realistic simulation of user movements.
"Our approach combines three-dimensional motion capture with biomechanical simulation," said Bachynskyi, a doctoral research student at Saarland University.

In optical motion capture a test subject wearing a special suit equipped with small optical markers performs a particular sequence of movements, such as waving his or her arms in order to control a computer game.
The markers on the suit emit light that is recorded by special cameras.
"To carry out the simulation, we use software to map these movements onto a model of the human body," said Bachynskyi.
To shed light on the actual biomechanical loads acting on specific body parts, the simulation programme calculates a number of key parameters: the joint angles, the forces acting on the joints at any time during the movement, as well as muscle activation and fatigue.

"The model allows us to see precisely which part of the body is subjected to the greatest loading when a particular movement is performed, and so we can determine whether, say, the upper arm muscles or the elbow are under particular strain," said Bachynskyi.
One of the cases studied by the researchers was how users interacted with a wall-mounted vertical touch screen.
They found that movements from left to right and from top to bottom put less stress on the muscles than forward and backward movements.
They concluded that a virtual keyboard is therefore best positioned in the lower central part of the screen.