I've been experimenting continously over the last week or two, since my previous post.
A number of concepts I proposed in the previous post have, empirically, been shown to be incorrect.
Among other things, I had theorised that due to the leftwards pelvic tilt (left side low, right side
high) both hip joints must be offset to the left of their pedals, and that therefore both legs must
be likewise offset to the left.
This is completely wrong.
The Main Issue
==============
My pelvic tilt, which is inclined to the left, causes the left hip joint to move downwards and
outwards, while the right hip joint moves upwards and inwards (towards the center of the body).
Normally, with a level pelvis, the legs descend vertically from the hip joints. With a pelvic
tilt, the legs are now angled - they still descend vertically from the pelvis, but the pelvis is
now tilted.
Consequently, the left leg now apparently reaches down further, while the right leg is apparently
lifted higher, while both feet are positioned to the *right* of their pedals.
Corrective action must be taken.
Firstly, saddle height is set correctly for the "longer" leg.
Secondly, the cleat on the shorter leg must have length adjusters added so that it is correctly
compensated for it's apparent shortening.
Thirdly, both cleats are offset to the left, so that both feet are offset to the right over
the pedals.
Both legs are now angled and so, compared to the bike frame, are not pushing downwards vertically.
However, compared to the pelvis, both legs *are* pushing downwards vertically - and THIS is the
crucial issue. It is THIS which determines comfort, correct muscle use and efficiency.
If the legs are made to push downwards vertically compared to the frame, rather than the pelvis,
then relative to the pelvis, the legs are pushing downwards *and sideways*. This is highly
uncomfortable, inefficient and improper.
Other Issues
============
Sitting on a saddle naturally tends to correct a pelvic tilt. With a pelvic tilt, the sit bones are
not level. The left sit bone is lower, the right sit bone higher. Sitting down on a saddle, however,
naturally brings both sit bones down onto the saddle, which causes, in my case, a partial
correction.
Consequently, where I had originally fitted leg length adjusters to compensate for the full apparent
leg length difference (about 9mm), I had over-adjusted, preventing the right leg from fully
extending.
I am now using 3mm of adjustment.
I have also tried manually holding my pelvis level, with no leg length adjusters and the cleats
centered. This worked, in that my legs were then held in the correct position. However, after two
rides testing this technique, I found - for the first time ever in my life - a touch of tenderness
below the skin centered on one of the fused upper vertebra. My conclusion is that such manual
position places undue stress on the fused upper spine, and I have desisted from this technique.
--
Callas