Have you ever tried running without swinging your arms? Scientists have found that the swing in your arms counter balances the movement of your legs and saves energy at the same time.
Christopher Arellano, from Brown University, US selected eight men and five women who were all committed runners.
Arellano asked them to run normally on a treadmill for 7 minutes as he measured their oxygen consumption rates and the amount of carbon dioxide that they exhaled.
Then he asked them to run without swinging their arms by holding the arms loosely behind the back, crossing the arms across the chest, and holding the hands on the top of the head.
"I think everyone conceded that the most challenging run was the one with the hands on the top of the head," said Arellano, who recalls the runners complaining about how tired their arms were at the end of the session.
Having measured the athletes' oxygen consumption rates and carbon dioxide production, Arellano then calculated the metabolic rates of each runner when they were swinging the arms and holding them in all three positions.
Comparing the four metabolic rates for each individual, researchers could see that swinging the arms reduced the runners' energy costs by 3 per cent relative to when they held their arms behind their backs.
Arm swinging also saved an impressive 13 per cent compared with when they held their hands on their heads.
The study was published in the journal of Experimental Biology.
