 Introduction
 Overview
 Five Central Concepts
 The Step Model and Footfall Plots
 Understanding the System
 Clinical Descriptions of Walking
 Gait Cycle (= Stride)
 Six Determinants of Normal and Pathological Gait
 Dispelling
the Step Length Myth
 Definitions
 Shorthand
Notation
(A) Introduction
A1. Overview
This method is derived using the 4 minimum points of gait
(stepheelpoint, steppelvic joint, rearpelvic joint, startheelpoint)
and the footline.
Lines and angles created by connecting these
points and line, defined at specific time points (snapshots) and projected
onto a 2D plane (usually the plane of the floor, but can be any), describe 8
fundamental parameters relevant to distance and direction for a person
walking. 3 define direction changes (foot offset, foot and pushoff angles),
4 for distances (stepout, straddle and rearleg lines, and pelvicstretch)
and 1 both a distance and direction change (aberration).
Walking is
the manipulation of these parameters.
These measurements are based on
the different parts of the body, and the specific actions, responsible for
distance and direction changes during a step. Any change of distance or
direction when walking must show as a change in at least one of the
fundamental parameters, so any movement that does not cause a change in at
least one will have no effect on distance or direction, in the relevant
plane.
This provides the basis for a primary classification system to
compare point, line, mass, etc. movements wrt their relationship to specific
distance and/or direction elements. Also, vertical movements are removed,
but they can be recorrelated separately, as can many other "outside"
factors, including time.
The true nature of many currently used measurements is also uncovered:
1) Stride length and walking base (straddle) are both
products of the same 9 distance and 5 direction elements, as well as 3 extra
distance and direction elements, if the measurement was taken at the point
of contact of the heel, instead of the heelpoint.
2) Current step
length (if left to right heel) is a product of 4 distance elements and one
direction element, and it does not accurately define the total distance
traveled by the foot over the step. If step length is defined as stride
length/2, then this is a measure of the stride, not the step.
3)
Etc., etc.,...
It's not surprising changes in step and stride lengths, etc. may be
difficult to correlate with changes of state for a subject. Each
contributing parameter is affected by different physical factors, and most
are independent of each other. That's at least 14 different body segment
lengths and joint rotations for stride and walking base.
This method
allows the measurement of all the fundamental parameters for every step. All
of the 14 values can be separately evaluated.
And, any path can be
recreated exactly using the individual Step Models. Then, comparison of
point and line movements with "standard" positions may show unique
information, or provide some other analytical aid.
All possible 2D
step patterns can be represented using the 8 parameters and described via a
very informative line description, for eg. L15{2}[15]str8: (2)L2L <4>R
(see Shorthand Notation) and/or a graphic Step Model. Every step, over a
single path or from different paths at different times, can be easily
compared side by side, or up and down, on a piece of paper (see Fig 16).
This is very, very useful for clinical applications. Patient progress
can be tracked via the 3 direction, 4 distance, and 1 distance and direction
defining elements. With relatively high accuracy and over any period of time
or conditions.
It also helps narrow the possibilities during
diagnosis. For eg., nothing changes straddle length (line) but rotations
(real or apparent) at the rearpelvic joint. But, rotation at that joint
also affects pelvicstretch, a distance change, and induces a foot offset, a
direction change. Foot offset is mainly changed by real or apparent
rotations at the step and/or rearpelvic joints. Etc., etc. Correlation of
changes in the various parameters will help pinpoint and track the problem
areas, and evaluate treatment options.
Clinical application has
extraordinary potential, but virtually all other facets of gait analysis
should benefit as well. An entire level of critical detail is being added.
There's also great flexibility and it's universal. It's just measuring
the distance and direction between projections of connected points, and is
valid for any arbitrary orientation of the 2D stepplane, at any point in
time, even if different minimum points are chosen.
How can it be
universal? Because it takes all the points and lines of reference from the
body itself. The reference frame moves with the person. There's no need to
be touching anything , no application of arbitrary, external references like
"line of progression."
This method removes the vertical component of
motion to provide a detailed, 2D picture of every step, which is easily
applied to a person walking on a treadmill, a rotating disk, around and/or
over objects, climbing stairs and inclines, in any physical condition
(including using a prosthesis), and on any surface; even floating in space,
crouching while walking or walking on the hands.
It allows the direct
comparison of how a person walks, for eg., on a rotating disk to how they
subsequently walk on a stationary plane, and how distance and direction
parameters change as the conditioning wears off. It can even be used to
study the detailed effects of multiple conditioning, since all the distance
and direction elements can be separately measured, and their variations
independently evaluated.
The minimum requirements are an overhead
view (or equivalent), and a way to identify the projection of the 4 points
and 1 line onto the desired 2D plane, at specific times. With current
technology, this should be almost trivial. One overhead camera, with visual
identification of the points, may be enough. 3D provides everything,
assuming the appropriate time coordinates can be extracted.
Also,
measuring changes in the parameters vs time over the path may be revealing.
It doesn't matter if one (or even both) heelpoint is in the air at the
snapshot, since the projection takes out the vertical part. After all, the
pelvic joints are always in the air. It just has to be interpreted properly.
And, the Step Model can also be used to produce "perfect" footfall
plots. Any or all of the fundamental parameters can be varied to see
distance and direction relationships between footfalls which couldn't be
studied without some kind of controlled model. Every possible 2D step and
path characteristic, wrt footfall position, can be plotted by varying the
parameters in the Step Model. This has been a very fruitful endeavor.
It shows, among other things, that a person can be walking a straight
line while turning with every step, and that measured equality of stride
length doesn't necessarily mean the person is walking straight, when
compared to another person who is also walking straight (see Fig 14).
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Part III
Part IV
Part V Copyright
© 2008
