Human
Postural Responses to Different Frequency
Vibrations of Lower Leg Muscles
A. POLÓNYOVÁ, F.
HLAVAČKA
Institute
of Normal and Pathological Physiology, Slovak
Academy of Sciences, Bratislava, Slovak Republic
Received June 8, 2000
Accepted November 30, 2000
Summary
We
analyzed human postural responses to muscle
vibration applied at four different frequencies
to lower leg muscles, the lateral gastrocnemius
(GA) or tibialis anterior (TA) muscles. The
muscle vibrations induced changes in postural
orientation characterized by the center of
pressure (CoP) on the force platform surface on
which the subjects were standing. Unilateral
vibratory stimulation of TA induced body leaning
forward and in the direction of the stimulated
leg. Unilateral vibration of GA muscles induced
body tilting backwards and in the opposite
direction of the stimulated leg. The time course
of postural responses was similar and started
within 1 s after the onset of vibration by a
gradual body tilt. When a new slope of the body
position was reached, oscillations of body
alignment occurred. When the vibrations were
discontinued, this was followed by rapid recovery
of the initial body position. The relationship
between the magnitude of the postural response
and frequency of vibration differed between TA
and GA. While the magnitude of postural responses
to TA vibration increased approximately linearly
in the 60-100 Hz range of vibration frequency,
the magnitude of response to GA vibration
increased linearly only at lower frequencies of
40-60 Hz. The direction of body tilt induced by
muscle vibration did not depend on the vibration
frequency.
Key
words
Postural
responses · Vibration frequency · Lower leg
muscles · Man
Reprint
requests
F.
Hlavačka, Institute of Normal and Pathological
Physiology, Slovak Academy of Sciences,
Sienkiewiczova 1, 813 71 Bratislava, Slovak
Republic. E-mail: hlavacka@unpf.savba.sk
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