Body biomechanics: Arm posture that propels

Jul 26 2014, 10:38 IST
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How we hold our arms affects how we run, but probably not in ways that most of us would expect. How we hold our arms affects how we run, but probably not in ways that most of us would expect.
SummaryPumping arms reduces the overall metabolic cost of running by helping to balance the moving body, increase forward propulsion.

How we hold our arms affects how we run, but probably not in ways that most of us would expect, according to a new study of upper body biomechanics. The ideal arm swing may be the one that you’re already using, the study concludes.

Distance running is, of course, physiologically costly, meaning that it requires large outlays of energy. Almost every aspect of the activity adds to that energy expenditure, like holding your body upright and metronomically swinging first one leg and then the other forward and toward the ground.

But scientists and some running-form coaches have speculated that pumping your arms, although requiring energy, reduces the overall metabolic cost of running by helping to balance the moving body, increase forward propulsion or, perhaps, provide a bit of bounce, helping to lift us off the ground with each stride. In this theory, swinging the arms makes it easier to run.

That idea, however logical it might sound, had not been proved. So for the new study, published last week in The Journal of Experimental Biology, researchers at the University of Colorado at Boulder invited 13 experienced adult runners to pull on their favourite running shoes and visit the university’s locomotion lab.

During their first session, the runners were fitted with masks to track how much oxygen they took in and carbon dioxide they puffed out. Those measures establish energy usage.

They ran on treadmills at a comfortable pace while holding their arms normally or in one of three increasingly unorthodox positions. In one instance, they held their arms loosely behind their back; in another, their arms were crossed at the chest, like a mummy’s; and in the last, they held their hands, fingers entwined, at the back of their skulls. In each case, volunteers ran for seven minutes, with a rest period between each run. Their respiration was monitored.

On a separate lab visit, the runners wore reflective markers on their shoulders, trunk and legs and repeated the four variations on arm positioning, as the researchers filmed them with three-dimensional motion-capture cameras.

The results showed, as the scientists had expected, that the volunteers used the least energy and were most efficient when they ran normally, their arms swinging at their sides. With each change in arm position, their efficiency dropped. Holding their arms behind their backs required 3 per cent more energy than running normally; draping them across their chests used 9 per cent more; and

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