Postural adjustment in individuals momentarily deprived of vision

Tania D. A. Fonseca
LACOM/NPT/UMC

Fernando H. Magalh?es
LACOM/NPT/UMC

Jos? A. Fernandes Lopes
DMR/HC/FMUSP

Daniel G. Goroso
LACOM/NPT/UMC

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     Last modified: March 15, 2007

Abstract
When an individual remains motionless, it does not remain without movement, its body oscillates. An adjusted motor action requires integration and continuous regulation of multiple proprioceptive and vestibular information, in normal condition and with lack of visual information. The purpose of this research was to quantitatively analyze the anticipatory postural adjustments (APA) and compensatory postural adjustments (CPA) of the trunk and inferior members? muscles through electromyography in individuals submitted to a momentary absence of vision. The movement task consisted of the following disturbance of the balance: fast extension of the trunk, starting at 90 degrees of flexion until upright posture. Kinematic and kinetic variables were used to locate the Instantaneous Point of Equilibrium (IEP) at upright posture. After the identification of this point, a window in the RMS data was selected to study the APA (tiep -200ms) and the CPA (tiep +200ms) caused by the auto-disturbance of the described movement of the muscles rectus abdominis (RA), lumbar ileocostal (IL), vastus lateralis (VL), semitendinosus (ST), tibialis anterior (TA) and lateral gastrocnemius (LG). The sample was composed of 10 male subjects, considered healthy and with 25.6?2.3 years old, 68.2?2.7 kg and 1.69?0.25 m (mean?SD). These subjects performed the tasks with a momentary absence of vision (MVA) and also with preserved vision (PV). ANOVAs showed that there are statistically significant differences (p<0.05) for both variables APA and CPA between the conditions MVA and PV. In the APA, significant differences had been found in the measures of RMS amplitude in the muscles RA, TA, and LG. CPA showed statistically significant differences in the muscles TA, ST and GL. During the MVA condition, such variation revealed more pronounced when it was compared to the PV condition. The preliminary results let us conclude that visual information is extremely important for modulating the muscular activity during postural adjustments.