Teach-in #12: What people said...

I thought about your observation regarding the paradoxical forward CoM
observation. Consider this to be an initiator of contalateral arm swing.



I would be very interested to see the VCM data that goes with this,
including the FP output, to get a feel of the gait associated with
these results (the web animation is not really smooth enough to get
a feel). Also can you provide details on where the heel and
particularly the toe marker were placed and the distance from the toe
marker to the end of the hallux. Thanks


Dear Jeremy,

Here's the GCD, but for some reason the forces don't seem to be in the
C3D file (also attached). I don't know why this is. There are 3 plates -
the first one was disconnected because I was using that to record other
data which I wanted to access in BodyBuilder (that's the only way to get
auxillary data in BB), and force plate 2 wasn't working (due to my
amazingly hopeless technician) but force plate 3 should have been
working. I was mainly interested in the CoM when I did the experiment
(which was for a completely different purpose than the Teach-in), so I
wasn't worried about the forces.

Anyway, sorry - you'll have to make do with the kinematics. I'm planning
on repeating the experiment when the lab is sorted out (Martin is coming
next week). As far as marker placement goes, this was standard VCM (toe
marker on head of 2nd M/T and os calcis at same level, 25 mm markers) -
the rest of the markers are Richard's CoM marker set. I do realise that
there should be an extra inch or so added in front of the toes marker
for the BoS, but considering that I'm underestimating CoM-BoS anyway, I
didn't think this was worth correcting. I'll do so in the next

The main point I wanted to make was that the CoM goes outside the BoS
twice every gait cycle. This is actually obvious when you think about it
(because the CoM has to move from the trailing foot to the landing foot
in a finite time while the latter is in the air), but BB gives us
something to look at.


Dear Chris,
Wow, what a fantastic page of design.
In "normal" gait, I look for the double support stage. If I see a gait
that does not have 2 feet on the ground in one form or another, I deem
that there is a problem. There could be many. The first thing that I
look for is a limb length discrepancy. I also find the length of time in
each phase of gait from heel contact to mid stance to toe off all very
As far as how the body keeps moving, I am of the belief that gait is
more due to the swing phase of the opposite limb, rather than propulsive
with the limb left behind. ( this is why on the last analysis we
differed in which muscle group was being used.

What do you think?



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