I found this online, and it was the basis of my question, earlier:
From
http://www.drmirkin.comDr. Gabe Mirkin's Fitness and Health e-Zine
October 28, 2007
Longer Lower Legs More Efficient
People who have longer lower leg lengths (the distance
from knee to ankle) will usually have greater endurance during
running or walking than those with shorter lower leg lengths.
Researchers at the University of Wisconsin showed that people
with longer lower legs use less energy when they run (Journal
of Human Evolution, August 2007).
In a previous paper in the same journal, these authors
showed that people with longer lower legs are better able to
prevent heat build-up, which slows you down and makes you
tired. When you exercise, almost 80 percent of the energy that
you use to power your muscles is lost as heat. So the harder you
exercise, the more heat you produce and the harder your heart
has to work to get rid of the extra heat. You prevent heat buildup
by your heart pumping hot blood from your muscles to the skin
where it is cooled by sweat and conduction and radiation.
People with longer lower limbs use up less oxygen and
produce less carbon dioxide for the same energy expenditure.
Therefore they are more efficient and can go further because
their bodies require less oxygen.