A3. The Step Model and Footfall Plots
The Step Model shows the body orientation at the instant of heel-contact,
at the end of the step. It can be used to make footfall plots which
re-create any 2D step or path characteristic.
Also, many things are
shown in the Step Model itself, so much (most) is gained just looking at the
model, without the need to make plots.
But, the footfall plots are a
very revealing part of the system. And very easy to make, despite the
apparent weight of the instructions. They're used to predict path
characteristics, given specific input, and should help greatly in the design
of experimental protocols.
If you start at a standard position on the
page and type in all the dimensions and co-ordinates for making the specific
models, it gets to be a very simple process. And, if the same base model is
used (ie., identical linear parameters), it's a matter of seconds to produce
The only rotation points are the step-heel-point for
rotating the step-foot model (for foot angle), and the step-pelvic joint for
the rotation of the step-out-line/step-foot model (for foot offset). 3
models per series can give most of the information, and one standard model
is all that's required for the 3, if only looking at direction parameters.
All of the direction changes are accounted for by rotating the whole model,
then aligning appropriate heel-points, and any changes of linear parameters
are taken care of when making the model.
Modeling using the Step
Model could be a big area. Since the procedure is exactly the same for all
plots, a computer program would be ideal to generate standard plots. This
would be an extraordinary project. And, actually relatively simple, though a
lot of details.
The final program would be very useful to facilitate
application to the diverse areas of gait research. It will allow the
generation of correlation tables for variations of the fundamental
parameters, wrt each other as well as other factors, like step and
stride-line. This will simplify the analysis of real footfall patterns. It
would also form the base program for integration of the 3rd dimension, and
other elements, in multi-D gait analysis programs.
When applied to
real data, itís the reverse of standard plotting. The data gives the Step
Models for each step, then each model is examined in detail.
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