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Sunday, December 19, 2010

Running and Breathing

On a recent NOVA podcast (09/03/2010 "Chasing Down Dinner"), David Levin talked about the way animals breath.

A quadruped mammal is four legged.  Cows, zebras, and dogs are examples.  In these animals, their stride is synchronized with their breathing.  A stride is one full cycle of leg movement while walking or running..  For instance, in a human, a stride is two steps.  When running, a quadruped's breathing is aided by the movement of the muscles and skeleton.

Here is a picture of a contraption put together by a physiology professor to teach how this happens.  "A" shows the animal moving the front legs forward during running.  The lungs expand at the same time and the animal inhales.  "B" shows the back legs coming forward and the animal would then exhale.  The ratio of stride to breath in a quadruped is 1:1.  One stride, one breath.  When the stride is lengthened, the volume of air into the lungs is increased.

As humans, our natural inclination is to also breath in synchrony to our stride.  But because we are upright and on two feet (bipedal) the ratio is different and can be more flexible.  The normal ratio is 2:1. Two strides to one breath.  A slow run can change that ratio to 4:1.

Humans, as a whole, are better adapted to endurance rather than speed.  Dennis M. Bramble, a biomechanist and vertebrate biologist at the University of Utah in Salt Lake City, and Daniel E. Lieberman, a biomechanist and anthropologist at Harvard University, have been studying the history of running in human beings.  They have come to the conclusion that our ancestors had an advantage with this ability to run long distances.  The animals they were chasing could not sustain a long distance.  Quadrupeds cannot pant when galloping, so their bodies would overheat and they would have to stop and try to cool off.  Meanwhile, the humans would continue in the chase and catch up.  The animals would then run again and soon were too overheated to run any longer, making it relatively easy to catch dinner.

Now you have heard something interesting.

1 comment:

  1. So what is the ratio to people like me who don't run! :)