"Let’s add one further influence of shoe heels, low to
high. The shoe’s elevated heel shortens the Achilles
tendon and there is also an accompanying shortening
of the calf muscles (Fig. 11). Both the tendon and the
muscles are, of course, vital to step propulsion and gait
stamina—which may help to explain the performance
dominance of marathon runners from nations where
the barefoot state is common from infancy to adulthood.
The heeled shoe “steals” much of this propulsive
power from the tendon and leg muscles. This not only
places more stress on them to achieve needed propulsion,
but power must be borrowed from elsewhere—
knees, thigh muscles, hips, and trunk. A small army of
anatomical reinforcements must come to the rescue of
the handicapped tendon and calf muscles."
from the first article.