Postural Organization of Gait Initiation for Biomechanical Analysis Using Force Platform Recordings

This method make it possible to obtain anticipatory postural adjustment, or APA. APA reflects the functioning of the central level system. It therefore make it possible to insert the question of what the APA, the MOS, and the BI look like.

The main advantage of this technique is precision. Moreover, it is a technique that has the possibility of being adapted, and less tiring for patient who have motor fixation, for example. The implication of this technique can be extended to all working pathology.

For Parkinson disease, it is especially interesting because it could help to find the mechanical marker for providing an earlier diagnosis or detecting subclinical balance and gait disorder. This method is applicable in certain sport, such as running start or sport with gesture with a still position, like shooting basketball or baseball. I think a person who have never practiced this method can also perform well.

You just have to be rigorous. To begin, ask the participants to stand barefoot and immobile on a force platform in their natural upright posture. With the arms hanging loosely against their sides and their gaze directed to a target at eye level at least five meters away.

Determine the participant's preferential starting leg by pushing lightly against their back while in the initial posture with their eyes closed to provoke a step forward. Explain to the participants that the tasks they are to perform is to initiate gait from the standing posture with the preferred leg. To continue walking to the end of the track and then return quietly to the initial standing posture.

Explain that gait is to be initiated following two successive signals, a preparatory signal and a departure signal. Then explain the instructions on velocity and temporal pressure. Trigger data acquisition from the force platform and deliver the first or preparatory signal to the participants.

Instruct them to stand immobile and avoid anticipating gait initiation at this first signal. Ensure that the participants are visually immobile. Check the immobility online with the time plots of the antero-posterior or medial lateral center of pressure displacement.

Then deliver the second or departure signal. Vary the conditions of temporal pressure imposed on gait initiation, and then vary the conditions of gait initiation velocity. Instruct the participants to perform a series of 10 successive trials in each experimental condition and impose a rest of at least two minutes between successive conditions to avoid the effects of fatigue.

In each condition, allow the participants to perform two familiarization trials before the recordings. Finally, stop the data acquisition once the participant has left the force platform. The biomechanical time plots obtained from the force platform during gait initiation and selected spacial temporal variables are shown here.

Gait was initiated quickly in a reaction time condition. The acceleration of the center of gravity and the velocity of the center of gravity along the antero-posterior, medial lateral and vertical directions are depicted here. The displacement of the center of pressure along the antero-posterior and medial lateral directions is also depicted in this figure.

The onset of anticipatory postural adjustments, or APA, along the media lateral and antero-posterior directions, time of swing heel off, time of swing toe off, time of swing foot contact and time of rear foot off are shown here. The figure also depicts the representative values of different temporal variables like time windows for APA, unloading phase and swing phase of gait initiation. The representative values of different spatial variables like antero-posterior velocity of the center of gravity at foot off and foot contact.

The maximal anticipatory center of pressure displacement, step length, step width, peak downward center of gravity velocity and vertical center of gravity velocity at swing foot contact time are shown here. The most important part of the foot occur is to ensure that the participant are visibly immobile in order to have a good baseline. Beside it is also important that the participant perform two formalization to have before the recording.

This will allow us to have a really better trial during the passages. So kinematic method can be used to add data during stationary working. I think might interest some researchers and think how they can use this technique in the field, from engineering to clinical replication.