[music]
When people develop calluses, not only do
they have thicker calluses as you might
expect but those calluses manage to
protect the foot without causing any
loss of sensory perception. The shoe
changes the mechanical properties of
that impact and it slows the rate at
which the collision occurs by about
three fold, and when that happens the the
area under the curve, which is the
impulse, the total amount of energy
that's delivered up your body to your
joints increases by about three fold, and
that means that when you're wearing a
shoe, your body experiences really
different forces than when you're
barefoot.
[music]
We traveled to western Kenya and did
research in two areas with the same
ethnic population, the Kalenjin, but we
were interested in the effects of shoes
and so we went to a rural population
where most people don't have shoes that
they can wear every day, and we compared
them to an urban population in the
nearby city of Eldoret. We brought an
ultrasound up to the field, measured how
thick people's calluses were. We brought
up a force plate, which is a kind of a a
very fancy device to measure how much
and how people walk, and we collaborate
with a team in Germany that, was able
to measure the sensory perception of the
foot at different frequencies and
different amplitudes.     It was exciting for
me first of all to demonstrate that, yes
indeed people who don't wear shoes tend
to develop thick calluses, which has not
been previously shown. On the other hand,
these calluses also provide protection -
 makes the skin harder, and then in
addition to that, these calluses do not
appear to dampen the tactile sensitivity
of our feet.     And of course we didn't
evolve to wear shoes, especially we
didn't evolve to wear cushion shoes, and
so one of the interesting questions that
this research raises, is we need
to understand more what that
consequences for joint damage.   [music]
