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Notice in
Figure 2, that when the hip extensors are maximally
stretched, a dynamic pull travels down the lateral leg
and tugs on the tibialis anterior/peroneus longus
stirrup.
Heel strike
during running activates this antigravity stirrup system
and delivers energy back up from through the biceps
femoris and sacrotuberous ligament where it combines
forces with other muscles to rotate the sacrum and
pelvis and counter rotate the lumbar spine (figure 3).
When working in perfect harmony with the other three
spring systems (described in the
Don’t Get Married article on my site), it
winds-up the intervertebral joints and deep ligamentous
structures creating the smooth cross-patterned gait
we’re used to seeing in highly functioning individuals.
However, if
the soles of the shoe are too cushioned or the running
surface is too soft, i.e., sand, the tib anterior and
peroneus longus stirrup can’t quite raise the arch and,
therefore, is unable to properly distribute ground
forces up through the biceps femoris and sacrotuberous
ligaments to help secure the sacrum on the ipsilateral
side. In an effort to get this stirrup spring system
going, the biceps femoris must exert greater force to
elevate the arch and this is where the problems begin.
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