The 'passive dynamic walking machine' used in the experiments.
Credit: University of Michigan
BOSTON: A new study explains why people swing their arms as they walk, a seemingly unnecessary movement for which researchers have tried to find an explanation.
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."
Walking machines
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.
Tendency to spin
The results showed that arm swinging, either normally or in the opposite direction, required little effort from the muscles. "Instead of being muscle-driven," Collins said, "arm swinging appears to arise from the natural dynamics, or passive dynamics, of the body as it walks."
The experiments also showed that keeping the arms steady increased the effort of walking by 12%, the equivalent of walking 20% faster or carrying a 10 kg backpack. When the arms were bound at the sides, not as much effort was needed, which suggests that holding the arms down requires more exertion that letting them swing.
But forcing the arms to swing out of sync increased the effort of walking even more. The researchers' explanation, which they developed by observing the walking robots, is that this alternate movement makes legs work twice as hard to prevent your body from spinning.
Arm movement...
Ever since I was a child, my left arm swings and my right does not. I have perfect mobility in both arms, and have never had any problems lifting things, driving, etc.
My dominant side is my right side, and I believe that my right arm may be double jointed at the shoulder. Could this have something to do with why it doesn't swing? Why would only one of my arms do it and not the other?
Sean (AZ, USA)
no arm swing
The article says perhaps you have CP or Parkinsons that will show up later on. It is most likely a nerve defect. If your shoulder on that side has abnormal flexibility you most likely need to seek a physical therapist to strengthen your rotator cuff. This would fix the lack of neurological problem. You just need to be very, very aggressive with your program. Hope this helps.
Swing Our ARMS
It is always observed that our human ancestors, primates when moving on biped(Two legs) swing their arms.
Toddler, first few steps when they attempt to walk also inadvertently move arms .The corresponding movements in a synchrony must be some thing to do with keeping constantly gravity while on move.. while carrying weight in both hands of course we don’t swing.
Armed forces when they perform marching, imagine movement without swinging arms looks as if a set of penguins are walking .
Let us continue with what nature taught us..
Talluri Vijai Kumar
Arm Swinging
When I was in the Royal Air Force we were obliged to swing our arms shoulder high or elbow high. The British style of drill appears very crisp and smart when done correctly. Sometimes we shared parade grounds with the American Air Force and were amused to observe their much more casual marching style. Now when I am running or jogging the arms held loosely bent also assist and when driving up hill, more vigorous use of the arms seems to help.
Stanley Northern Ireland