Is the regulation of the Center of mass maintained during leg movement
under microgravity conditions ?
Mouchnino, L., M. Cincera, J.C. Fabre, C. Assaiante, B. Amblard, A. Pedotti,
Laboratory of Neurobiology and Movements, CNRS, 31 chemin Joseph Aiguier,
13402 Marseille cedex 20, FRANCE, Faculty of Sport Sciences, 163 av. de Luminy
13288 Marseille cedex 9, FRANCE, Centro di Bioingegneria, Politecnico, via
Gozzadini 7, Milano, ITALY.
APStracts 3:0037N, 1996.
SUMMARY AND CONCLUSIONS
1. Investigations on stance regulation have already suggested that the body's
center of mass is the variable controlled by the central nervous system to
maintain equilibrium. The aim of this study was to determine how the center of
mass of the body is regulated when leg movements are made under different
gravito-inertial force conditions. 2. Kinematic and electromyographic (EMG)
recordings were made during both straight-and-level flight (earth-normal
gravity condition, nG) and periods of weightlessness in parabolic flight
(microgravity condition, G). The standing subjects were restrained to the
floor (kept from floating away in G) and were instructed to raise one leg
laterally to an angle of 45 degrees as fast as possible. 3. Two modes of
center of mass (CM) control were identified during leg movement in nG: a
"shift mode" and a "stabilization mode". The "shift mode" served to transfer
the CM towards the supporting side prior to the leg raising and it preceded
the phase of single limb support. The "stabilization mode" took place after
the CM shift was completed and was aimed at stabilizing the CM during raising
of the leg. In this phase, the movement of the raising leg is counterbalanced
by a lateral inclination of the trunk in the opposite direction. As a
consequence, CM position did not change with respect to the position reached
before the leg raising and its projection on the ground remained within the
support area delineated by the stance foot. 4. Under G, the CM position did
not change before the leg raising. Moreover, Gastrocnemius Medialis activity
observed in the moving leg under nG, preceding the initiation of the body
weight transfer towards the supporting leg, was greatly reduced. While the leg
is raising, the simultaneous and opposite lateral trunk movement was still
present in G. 5. Results suggest that the body weight transfer corresponding
to the "shift mode", might depend on the gravity constraints, while the
"stabilization mode" which remains unchanged in G might be a motor stereotype
which does not depend on the gravity conditions.
Received 1 September 1995; accepted in final form 19 January 1996.
APS Manuscript Number J578-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 14 February 96