There’s a brief piece in Science this week about bouncy legs -- how the calculus predicts that locomotion on stiff legs is most efficient and yet all of us -- and small critters especially -- bounce about when we move.
A new computer model nails the reason why:
Integrative physiologist Monica Daley of the Royal Veterinary College (RVC) in Hatfield, U.K., had observed how adeptly the guinea fowl, an African bird known for its running skill, negotiated sudden drops and other obstacles. She wondered how the shape of an animal's body and the nature of the terrain -- details left out of earlier simulations because they're difficult to model -- would alter the models' predictions.
So she and RVC colleague James Usherwood devised a computer model that didn't sidestep the complexities of animal motion. Instead of attaching legs to an idealized point with a certain mass, the new model linked them to a bouncing body -- the seesawing guts and other tissue an animal carries as it moves -- and set them on an uneven course.
As Daley expected, the less-idealized runners fared better on compliant legs. The spring in their step offset the bounce of their bodies, resulting in a smaller energy cost. "That's interesting and quite novel," says biomechanist Manoj Srinivasan of OhioStateUniversity in Columbus, who was not involved with the research. 
This is a lovely nod to the impact of terrain on our evolutionary development and only adds fuel to my long simmering theory that we are born and made and shaped by place; that each of us carries our own terroir and inherits some from those who came before us.
That, like wine, we are seasoned by our soil.
It also reminds me of a conversation I had with my dad when I was small and we were navigating the precarious paths of Mesa Verde. I was terrified. “Walk like an Indian,” he told me. “Bounce a little bit.”
I don’t know where he received this intelligence (it well could have been while he was rambling through the desert with Native American friends in search of peyote buds; it may have come to him after they were consumed; it was probably from the pages of a book) but it turns out it works. I deployed it at Mesa Verde -- with success -- and I've found whenever I’m uncertain about my footing on rough trails that exaggerating the spring in my step gets me through the worst of it (with some adjustments in the presence of scree).
Works on mountain bikes, too.
It’s counter intuitive, because when fear settles in while walking the cliff’s edge the instinct is to go rigid and inch your way along in terror. But it's also old news, isn't it: like the drunk who emerges unscathed from the crash with the upright toppled and dying around him, or the reed that bends in the wind.
It's the pliable who survive.
 Gisela Telis, Why Bouncy Legs Work Better, Science 23 March 2010
p.s. the apes are still lumbering for a little while longer yet »