Human beings transition between from one style of gait to another as they transition from walking to running (see figure, above). The act of walking is fundamentally one of transferring weight from one limb to another, while running is primarily an act of maintaing inertia. Furthermore, these two gaits apparently have their origin in the minimization of energy costs associated with moving at a particular speed1.
Interestingly, it seems that snakes do not make any such transition in their locomotive behavior. A study appearing in the Proceedings of the National Academy of Sciences has used theoretical modeling, friction measurements, and slithering-observations to demonstrate that snakes simply "speed-walk" at high speeds 2. Although they have no limbs, and thus no "gait" to speak of, at slow speeds, they do move about by transferring weight from one part of their body to another. In contrast to other animals, however, they do the same thing, only faster, at high speeds. It is unclear why speedwalking is not an undue energetic costs for these animals, perhaps there is simply no less-costly way to move about. Further work will be needed to more completely understand the energetics of snake locomotion.
References:
1. Srinivasan M, Ruina A. (2006) Computer optimization of a minimal biped model discovers walking and running. Nature. 439(7072): 72-75.
2. Hu DL, Nirody J, Scott T, Shelley MJ. (2009) The mechanics of slithering locomotion. Proc Natl Acad Sci U S A. [Epub ahead of print]
PMID: 19506255 [PubMed - as supplied by publisher]
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