The research, detailed today in the Proceedings of the Royal Society B, used simple robots and human experiments to show that arm swinging is both easy and beneficial. The movement requires little muscular effort, yet it makes walking much easier.
“This puts to rest the theory that arm swinging is a vestigial relic from our quadrupedal ancestors,” said Steven Collins, a biomechanical engineer with the University of Michigan in the USA. “Instead, arm swinging is a sensible part of an economic gait on two legs.”
Collins first became interested in the role of arm swinging through his work with walking robots, which he uses to test ideas about human locomotion. He works with ‘passive dynamic machines’, which walk down a small incline without any power source, as well as robots that use motor-driven springs to push off the ground.
However, the first machines had trouble walking without arms, tending to spin and fall. When Collins and his colleagues added free-swinging arms to the machines, they moved in a way similar to human arms.
The researchers designed an experiment to determine the purpose of this arm swinging. They had 10 people use their arms in different ways as they walked: either swinging normally, held at their sides, bound to their sides or moving out of sync to the walking.
They measured the effort required from the shoulder muscles, as well as the effort of walking overall, which was quantified as metabolic cost.”