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fpassariello98
02-21-2003, 07:59 AM
Dear Colleagues,
in this message you'll find a short english abstract about a postural model presented to a Congress in Italy.

The work is based on the well known classical inverted pendulum model and a recovery step is introduced as an answer to deterministic or random perturbations.
The architecture of the control is based on the notion of feedback in the space of the states. The architecture of the planning is based on an algorithm whose input consists of two indices which are defined in the phase space.
The complete work is outlined in a Physics Thesis, december 2001, in italian language, a long document (almost 120 pages) which can be retrieved at the following address

http://www.na.infn.it/Gener/cyber/report.html

Dott. Fausto Passariello
Vascular Surgeon

Centro Diagnostico Aquarius
Via Francesco Cilea, 280 Napoli
80127 Italia
Web Page http://web.tiscali.it/afunc
EMail: afunzionale@tiscalinet.it

Here follows the abstract:
====================
GIORNATE SCIENTIFICHE del POLO delle SCIENZE e delle TECNOLOGIE per la VITA

FacoltÓ di Medicina e Chirurgia, Farmacia, Medicina Veterinaria e Agraria

Portici, 6 - 7 Giugno 2002

HUMAN POSTURE DURING STANDING.

CONTROL AND PLANNING OF BALANCE.

F. Passariello, G. Trautteur.

Department of Physical Sciences. Federico II University, Naples.

INTRODUCTION - Bipedal standing position is typical of the human being. The quantitative

experimental detection of the postural adaptations while standing is effected by means of the

stabilogram. In 1995 Collins and De Luca (1) introduced diffusion analysis. In 1997 Pai and

Patton (2) delineated theoretically the regions of the phase space compatible with

equilibrium.

METHODS - The model foresees the study only of the anterior-posterior movements in the

sagittal plane of an inverted pendulum and of the relationships in the phase space between

centre of pressure (COP) and centre of mass (COM). A recovery step may transfer the

pendulum to a condition with a small probability of fall. The architecture of the control is

based on the notion of feedback in the space of the states. The architecture of the planning

is based on an algorithm whose input consists of two indices which are defined in the phase

space. They are the index of recovery (REC) and the index of transfer (TRA).

RESULTS - A random perturbation makes the control very sensitive to the initial conditions of

the movement (position and speed). The COP fluctuates around the position of equilibrium

(trembling) and in the phase space the trajectory oscillates forming a random ball around a

dynamic attractor, while the recovery step is visualised like a horizontal line, that shifts the

system into a different REC zone. When the system has been given a point of reference

much shifted toward the forefoot, the acceleration causes a continuous unbalance that

determines a succession of recovery steps. This behaviour could be the point of departure of

a study of the bipedal deambulation. In all the simulations are present two phases of the

scaling plot, where the second phase is flat, in contrast with the experimental measurements.

Vice versa in the first phase of the scaling plot the inclination is comparable to that reported

in literature and comparable with that of the so-called open-loop phase of Collins. The

scaling coefficient of the first phase is strongly influenced by the initial conditions, a fact

which could be the point of departure of a critical revision of the open-loop model.

CONCLUSIONS - This research introduces a simple, original and analytical method for the

outline of the phase space partition, which can also be used in the analysis of the posture

when in presence of external perturbations. The algorithmic model runs are in good

agreement with the biological behaviour, despite its simplicity. Particularly, the posture in

static conditions and the deambulation could depend on an unique control mechanism, in

which only the point of reference of the feedback has varied.

REFERENCES

1. J.J. Collins, C.J.De Luca: Open-Loop and closed-Loop control of posture: A random-walk

analysis of center of pressure trajectories. Exp. Brain Res., (95):308,1993.

2. Y.C. Pai, J. Patton: Center of mass velocity-position predictions for balance control. J.

Biomechanics, 30(4):347-354, 1997.

3. F. Passariello: Modello dell'Equilibrio Posturale Umano nella Stazione Eretta. Tesi di

laurea in Fisica. Relatore: Chmo Prof. G.Trautteur. Dicembre 2001.

Email: afunzionale@tiscalinet.it

Web page: web.tiscali.it/afunc

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