The Mouck Method for Gait Analysis & Path Deviation Study

Part I - Introduction, Definitions and Shorthand Notation

(B) Understanding the System

A person walking is a mechanical instrument. The brain uses muscles to manipulate a lever (vector) and point system to carry the body in any direction. Though the brain is in control of all the muscles, the lever and point system defines distance and direction.

As with any system, there are disadvantages and advantages to its study. Some are outlined below:

Disadvantages:

• since human subjects – averages and trends rather than exact
• could be large variations in step characteristics within a few strides or with every step
• not easy to measure angles and distances in field experiments
• everyone has distinct physical characteristics and learning which make the way they walk unique
• angle and offset values could be small – a few degrees, or less than 1 inch offsets, possibly
• knee, ankle and hip joint rotations complicate the picture

Advantages:

• a person walking is a vector system
• the path of the foot in the air doesn’t matter, only the final foot placement.
• know starting point each time, the footfall
• feet are attached through the leg and pelvis.
• even though everyone’s walk is unique, all direction and distance changes are definable using the 8 parameters.
• not necessary to identify and understand every control factor for leg movement, many can be generalized to standard influences.
• all the upper body is irrelevant to the distance and direction measurement
• footfall patterns are linear, continuous and sequential.
• effects of terrain, spins, slides, and other aberrant step characteristics resulting in heel-point shifts and/or foot-line rotations (ie. aberrations) can be separated and incorporated later, making the initial discussion much simpler.
• can define a “perfect” model system.

B1. Clinical Description of Walking

A stride, or gait cycle, can be discussed in several ways. One is to describe leg movement as in a swing or stance phase. The swing phase is when the foot is in the air (carry and step) and the stance phase when the foot is planted. The stance phase is further separated into single (one foot planted) and double (both feet planted) stance phases.

a) Gait Cycle (= Stride)

Swing phase: - one/stride, 40% of the gait cycle
    - foot is in the air and moving forward through the carry and then step
    - other foot is in single stance phase
Stance phases:
    Single stance phase: - one/stride, 40% of the gait cycle
        - foot is planted and the leg used to vault the body forward
        - other foot is in swing phase
    Double stance phase: - two/stride, 10% of the gait cycle each
        - both feet are planted
        - one foot going toe-off to swing phase (behind), the other heel-strike to toe-off (in front)

These phases are further sub-divided with respect to forces, etc., but there’s no need to go into that.

Clinical work also describes six determinants of normal and pathological gait in an attempt to describe the most important physical parameters involved in walking.

b) 6 Determinants of Normal and Pathological Gait

These are generally (though far from universally) presented as describing the factors important for affecting gait, and are usually explained as an attempt to minimize the energy cost of walking by reducing the movement and position of the body’s center of gravity (COG). The COG moves side-side (lateral sway), and up-down in a normal gait cycle. (Saunders JB, Inman VT, Eberhart HD. The major determinants in normal and pathological gait. JBJS 1953; 35-A:543-58.)

1. Pelvic rotation – the pelvis rotates forward at heel strike and backward at toe off to increase the effective leg length and decrease the drop of the COG.
2. Pelvic list – the pelvis tilts down at toe-off and heel-strike to increase the effective leg length and decrease the drop of the COG.
3. Stance phase knee flexion – flexing the knee of the planted leg decreases the rise of the COG over the single stance phase.
4. Ankle rockers – stretching the foot out at toe-off and contracting it back at heel-strike increases the effective leg length and decreases the drop of the COG.
5. Transverse rotation of leg segments – ie. changing foot angle.
6. Genu valgum – the anatomy of the knee allows sideways motion at the joint. When “knock-kneed,” there appears to be less lateral sway of the COG.

Item #5 is the only one directly related to direction change.
All the others would affect direction and/or distance if deviations caused the foot to be planted differently.

For non-pathological gait, all contribute to the walking characteristics leading to normal aberrations, foot and push-off angles and foot offsets.

Even in clinical research, many use the inaccurate definition for step length as the distance from one foot strike to the next (L-R and R-L). This would usually give a value greater than the real step length, and it varies differently than the accurate measurement.

So, some step length deviations interpreted from R-L, L-R or stride length changes may actually be caused by foot angles and offsets.

No matter, these studies still may give clues to important factors for the control of direction in walking, and where to start looking to understand deviations.

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