Deceleration affects anticipatory and reactive components of triggered postural responses |
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Authors: | Mark?G?Carpenter Alf?Thorstensson Email author" target="_blank">Andrew?G?CresswellEmail author |
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Institution: | (1) Department of Neuroscience, Karolinska Institutet, Box 5626, 114 86 Stockholm, Sweden;(2) University College of Physical Education and Sports, Stockholm, Sweden;(3) School of Human Kinetics, University of British Columbia, Vancouver, Canada;(4) School of Human Movement Studies, University of Queensland, Brisbane, Australia |
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Abstract: | Understanding the physiological and psychological factors that contribute to healthy and pathological balance control in man
has been made difficult by the confounding effects of the perturbations used to test balance reactions. The present study
examined how postural responses were influenced by the acceleration–deceleration interval of an unexpected horizontal translation.
Twelve adult males maintained balance during unexpected forward and backward surface translations with two different acceleration–deceleration
intervals and presentation orders (serial or random). “SHORT” perturbations consisted of an initial acceleration (peak acceleration
1.3 m s−2; duration 300 ms) followed 100 ms later by a deceleration. “LONG” perturbations had the same acceleration as SHORT perturbations,
followed by a 2-s interval of constant velocity before deceleration. Surface and intra-muscular electromyography (EMG) from
the leg, trunk, and shoulder muscles were recorded along with motion and force plate data. LONG perturbations induced larger
trunk displacements compared to SHORT perturbations when presented randomly and larger EMG responses in proximal and distal
muscles during later (500–800 ms) response intervals. During SHORT perturbations, activity in some antagonist muscles was
found to be associated with deceleration and not the initial acceleration of the support surface. When predictable, SHORT
perturbations facilitated the use of anticipatory mechanisms to attenuate early (100–400 ms) EMG response amplitudes, ankle
torque change and trunk displacement. In contrast, LONG perturbations, without an early deceleration effect, did not facilitate
anticipatory changes when presented in a predictable order. Therefore, perturbations with a short acceleration–deceleration
interval can influence triggered postural responses through reactive effects and, when predictable with repeated exposure,
through anticipatory mechanisms. |
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Keywords: | Human Kinematics Motor control Proprioception |
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