Kaze Uta Budo Kai Forum Archive

Out on a limb: Arm-swinging riddle is answered

PARIS (AFP) – Biomedical researchers on Wednesday said they could explain why we swing our arms when we walk, a practice that has long piqued scientific curiosity.

Swinging one's arms comes at a cost. We need muscles to do it, and we need to provide energy in the form of food for those muscles. So what's the advantage?

Little or none, some experts have said, contending that arm-swinging, like our appendix, is an evolutionary relic from when we used to go about on all fours.

But a trio of specialists from the United States and the Netherlands have put the question to rigorous tests.

They built a mechanical model to get an idea of the dynamics of arm-swinging and then recruited 10 volunteers, who were asked to walk with a normal swing, an opposite-to-normal swing, with their arms folded or held by their sides.

The metabolic cost of this activity was derived from oxygen consumption and carbon dioxide (CO2) production as the human guinea pigs breathed in and out.

Arm-swinging turned out to be a plus, rather than a negative, the investigators found.

For one thing, it is surprisingly, er, "'armless" in energy costs, requiring little torque, or rotational twist, from the shoulder muscles.

Holding one's arms as one walks requires 12 percent more metabolic energy, compared with swinging them.

The arms' pendulum swing also helps dampen the bobbly up-and-down motion of walking, which is itself an energy drain for the muscles of the lower legs.

If you hold your arms while walking, this movement, called vertical ground reaction moment, rises by a whopping 63 percent.

Should you prefer to walk with an opposite-to-normal swing -- meaning that your right arm moves in sync with your right leg and your left arm is matched to the motion of your left leg -- the energy cost of using your shoulder muscles will fall.

The downside, though, is that opposite-to-normal swing forces up the metabolic rate by a quarter.

The study, headed by Steven Collins at the University of Michigan at Ann Arbor, says we should give the thumb's-up to arm swinging.

"Rather than a facultative relic of the locomotion needs of our quadrupedal ancestors, arm swinging is an integral part of the energy economy of human gait," says the paper.

It appears in Proceedings of the Royal Society B, the biological research journal of the Royal Society, Britain's de-facto academy of sciences.

http://news.yahoo.com/s/afp/20090728/sc_afp/sciencearmsoffbeat

Great article. After reading it though I couldn't help but ask the question, "How does this relate to same hand, same foot." Seems to me it helps to concentrate energy to the movement. Anyone else have any thoughts?

At the risk of showing my ignorance I will throw my thoughts in the ring. The same hand same foot idea primarily comes in movement when we want to attack or deflect or otherwise deliver power to our partners body. The same hand same foot idea puts me in position to deliver the power, but the power comes from the line of the trailing foot (opposite foot) on the floor through the delivering hand and into the body of your partner. Kind of like pushing a car one handed, in theory you could lift the leading foot off the ground and still be applying the push from the ground through the opposite foot through your body and hand and onto the car. There are two reasons I have been thinking this way: one) a while back we were working with tori taking different movements from the same shomenate attack. In one, tori drops almost directly back while making contact with uke's hand. I was applying the same hand same foot idea so if I made contact with ukes hand with my right hand and then dropped back, I would drop back with my right foot. However, to get the "wave" action we were searching for, Nick and other seniors were dropping back with the opposite foot, 2)two, in jyodo when I watch my instructors deliver a push they are in the same hand same foot position, but the pushing power is coming from the back foot.

I don't know if that helps, or even if I am on the right track, but it is the way my thoughts have currently been running.

I am far from an expert, but I like it Scott. Seems pretty logical to me. It is interesting your observation about the drop back. I imagined the use of the center in a differenr way when I read that. Could be what you are eluding to. Kind of like the window washing step in the walk.

I apologize Doug that I can't remember the exact setup to the technique I tried to describe. However, maybe I can describe a little drill to try the next time you are in Aikido. If you do Judo, it has the same feeling as the setup to a linear osoto gari.

Have your partner slowly attack you with a shomen ate strike with their left hand. You meet that strike with your own unbendable right arm but drop back slightly off line with your left leg. As soon as your left foot grounds, then push back into uke with the power of your left foot (your right leg stays ahead of your left leg in the leaving you in the same hand same foot position). Your right hand should remain in contact with their left hand/wrist etc. I have not tried this yet, I am just trying to replicate the feeling in my head and then onto paper.

I would welcome any other thoughts from anyone on this discussion, especially since I may be going down the wrong track.

I'm confused.
Maybe it's because my arms don't swing when I walk, they drag alongside my feet.