Ever bumped into someone while texting? A new study sheds light on why walking and texting is such a difficult multi-task.

Researchers examined the gaits of 26 subjects given three different tasks in a study published in PLOS ONE: walking without a phone, walking while reading on a phone, and walking while texting on a phone. Not surprisingly, the participants swerved and slowed down the most while texting.

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Researchers tracked the subjects' movements over 8.5 meters using a three-dimensional movement analysis system. Reduced arm swing may account for some of the slowdown, the researchers wrote, as the arms usually remain locked to the thorax in texting position. Arm swing is also essential to recover balance.

The altered head posture -- the head moves more when reading or texting -- reduces vestibular input, which is essential for your body to navigate its way through the world.

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While theory holds that when faced with two simultaneous tasks, the brain would prioritize gait stability over a cognitive task like texting, the researchers found that young, healthy people can choose to prioritize the cognitive task when they perceive the situation to provide a sufficient safety buffer.

So, the brain of a young adult walking down an empty sidewalk may be focused more on the message he's composing to his girlfriend than on navigating his route. Still, even in the group of 26 healthy people who the researchers studied, nine reported previous texting-related accidents.