EQUIPMENT
Postural sway was evaluated by means of a
force measuring system, which consisted of a
force plate (Kistler Z-4305, Winterthur, Switzerland).
The foot-ground reaction forces in
the anteroposterior and mediolateral directions
were monitored on-line for each foot during
the test. These are the tangential components
of the force signal responsible to maintain
equilibrium during standing and exerted by
the body at the foot level. The time variation in
these forces reflects the swaying motion of the
body in the horizontal plane. The force signals
from the Kistler amplifier (type 9803), with
gains set at 5 Newton volt' for the mediolateral
and anteroposterior directions, were routed to
a computer through a multichannel analogue
to digital converter at a sampling rate of 50 Hz.
The force traces obtained included transient,
slow (approximately 0.1 Hz) upon which more
rapid (1 Hz and higher) oscillations were superimposed.
A numerical procedure was set to
rectify these rapid oscillations and to compute
their average amplitudes.'4 The baseline of the
rapid oscillations was established by computing
the point by point moving average of the signal.
The computation was based on 100 samples, 50
on each side of the time point. To allow comparison
between the different tests and subjects, the
averages obtained were normalised to the body
weight of each of the subjects and expressed as a
percentage of body weight (%W).
PROCEDURE
Before testing all subjects received a
EQUIPMENTPostural sway was evaluated by means of aforce measuring system, which consisted of aforce plate (Kistler Z-4305, Winterthur, Switzerland).The foot-ground reaction forces inthe anteroposterior and mediolateral directionswere monitored on-line for each foot duringthe test. These are the tangential componentsof the force signal responsible to maintainequilibrium during standing and exerted bythe body at the foot level. The time variation inthese forces reflects the swaying motion of thebody in the horizontal plane. The force signalsfrom the Kistler amplifier (type 9803), withgains set at 5 Newton volt' for the mediolateraland anteroposterior directions, were routed toa computer through a multichannel analogueto digital converter at a sampling rate of 50 Hz.The force traces obtained included transient,slow (approximately 0.1 Hz) upon which morerapid (1 Hz and higher) oscillations were superimposed.A numerical procedure was set torectify these rapid oscillations and to computetheir average amplitudes.'4 The baseline of therapid oscillations was established by computingthe point by point moving average of the signal.The computation was based on 100 samples, 50on each side of the time point. To allow comparisonbetween the different tests and subjects, theaverages obtained were normalised to the bodyweight of each of the subjects and expressed as apercentage of body weight (%W).PROCEDURE
Before testing all subjects received a
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