Analysis of the variability of the Gait Cycle

Walking is a very complex movement; it requires the integration of many acting muscles, bones and signals, all control by the central nervous system. The mechanism operates with a small base support and its center of mass is located far away form the ground.

When we walk we have to have the total control of the swing, so we can take off one leg from the ground and land it again, but we also require a neural control when some dangerous perturbations appear.

For the purpose of analysis we can take in consideration two kind of variables, measurable variables (stride length, step length, joint angles, ground reaction forces, electrical activity of muscles EMG, metabolic energy and rate and cadence) and model based variables (joint forces and torque, mechanical work and power, and mechanical energy). All this variables are outcome measures so with them we cannot have an idea of the organization of the natural control. However they can provide an explanation of it (organization of the natural control).

In this analysis we are going to determine the variability of the phase diagram between the hip, knee and ankle joints during level walking. The first step is to record these joints in the Gait Lab and then eliminate the time and present the phase diagrams during the gait cycle.

The gait cycle is the elementary sequence of walking. It starts when the heel of one leg touches the ground and ends just before the same heel touches the ground again. We cannot define the “normal walking”, because there are differences between each person, depending on if it is male or female, age, race, etc.

The gait cycle has two distinct phases:
·    Stance phase: when the foot is at the ground, last for 60 to 65% of the gait cycle.
·    Swing phase: when the foot is off the ground, last for 35 to 40% of the gait cycle.

We can also classify the gait cycle based on the number of legs contacting the ground:
·    Double support phase (DSP): Is when both legs have ground contact. Starts at the same time as the stance phase but ends when the collateral leg starts to swing. Last between 16 and 20% of the gait cycle.
·    Single support phase (SSP): Is when one leg has ground contact. It is equivalent to the swing phase.

The duration of the swing phase changes very little,depending on how fast you walk,so the variation of the stance phase determines the duration of the gait cycle.

The stance phase has sub-phases:Heel-contact,foot-flat,heel off and toe off.Some just use 3 sub phases:early-,mid-and late-stance phase.

The swing phase has also sub-phases:initial-and terminal swing,and initial-and terminal extension,and in a different terminology to early-,mid-and late swing.If the steps with the left and right leg are identical and the time shifted for 50% of the gait cycle,the walking is symmetrical.

To quantify the kinematics of walking we have to select the system of reference. Movement can be defined with external references,internal coordinates or the phase plane formed by selecting state variables. For the analysis of walking we can reduce the 3D movement to a 2D movement,assuming that all points of the body are moving in planes parallel to the sagital plane.We can describe the movement by making a relation with the neighboring segments and the internal coordinates.We have to assume the segments of the body as rigid bodies,so joint angles define walk.

The typical joints angles used to describe walking are:

                Ankle          = - -
                Knee               = -
                Hip                 -

The phase reference frame is used to characterize the relationship between some internal and external coordinates during the walking. The state space trajectory shows implicitly how a specific pint is moving in time. The diagrams show the repetitive nature of movement. [Popovic, Sinkjær,2003].

The gait lab uses a Television Computer System that works with a charge-coupled device (CCD) system. This systems work with electronically shuttered, 8  infrared cameras that work at a 240 frames per second for the enhancement of passive markers, that are semi sphere shape and cover bye retro-reflective adhesive sheet. The 8 cameras are placed all around the room and they are connected to a common network. The software used was Qualisys Track Manager, from which we got all the data as a .qtm file. Then, we exported the QTM file into a .tsv file with just the identified trajectories in an specific order that Mathematica program will recognize. We imported the .tsv file and manage data with Mathematica for making our analysis, and we created with this the final .html file.

To obtain this data and to make an analysis of the gait cycle we used the Peak (Kit Vaughan) parameters. Which is shown in the next figure:

1.    Metatarsal
It is positioned on the medial aspect of the metatarsal head. This marker the medial reference point for the foot, it is useful to obtain information about the foot, it works together with the Heel marker.

2.    Heel
Placed on the heel and they work together with the metatarsal markers.

3.    Lateral malleolus
These markers are the lateral distal reference point for the shank and the lateral proximal referee point for the foot. It is place on the lateral malleolus.

4.    Tibial
These markers are used just for the tracking of the shank

5.    Lateral Epicondyle
As it name says, these markers are placed on the lateral epicondyle. They are the lateral distal reference point for the thigh and the lateral proximal reference point for the shank.

6.    Greater trochanter
This pair of markers is placed on the greater trochanter of femur. As the superior iliac crest, these markers are also used as proximal reference points, but in this case they are for the thighs.

7.    ASIS
It is placed on the anterior superior iliac spine. This marker working together with the sacrum markers, provide information about the pelvis.

8.    Superior iliac crest (We used this more marker, just for reference)
Placed on the superior iliac crest. These markers can be used as proximal reference points for the trunk.

Video Example

Created by Mathematica  (October 25, 2004)