This method is derived using the 4 minimum points of gait (step-heel-point, step-pelvic joint, rear-pelvic joint, start-heel-point) and the foot-line.

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 push-off angles), 4 for distances (step-out, straddle and rear-leg lines, and pelvic-stretch) 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 re-correlated 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 heel-point.

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 re-created 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)L-2L -<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 rear-pelvic joint. But, rotation at that joint also affects pelvic-stretch, 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 rear-pelvic joints. Etc., etc. Correlation of changes in the various parameters will help pin-point 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 step-plane, 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 co-ordinates 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) heel-point 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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