Directional specificity of postural muscles in feed-forward postural reactions during fast voluntary arm movements

Abstract

Healthy subjects performed bilateral fast shoulder movements in different directions while standing on a force platform. Anticipatory postural adjustments were seen as changes in the electrical activity of postural muscles as well as displacements of the center of pressure and center of gravity. Postural muscle pairs of agonist-antagonist commonly demonstrated triphasic patterns starting prior to the first electromyographic (EMG) burst in the prime-mover muscle. Proximal postural muscles demonstrated the largest anticipatory increase in the background activity during movements in one of the two opposite directions (forward or backwards). These changes progressively decreased when movements deviated from the preferred direction and frequently disappeared during movements in the opposite direction. The patterns in distal muscles varied across subjects and could demonstrate larger anticipatory changes during movements forward and backwards as compared to movements in intermediate directions. Bilateral addition of inertial loads to the wrists did not change the general anticipatory patterns, while making some of their features more pronounced. Anticipatory postural adjustments were followed by later changes in the activity of postural muscles, also reflected in the mechanical variables. Changes in leg joint angles revealed a "hip-ankle strategy" during shoulder flexions and an "ankle strategy" during shoulder extensions. The study demonstrates different behaviors of proximal and distal muscles during anticipatory postural adjustments in preparation for fast arm movements. We suggest that the proximal muscles produce a general pattern of postural adjustments, while distal muscles take care of fine adjustments that are more likely to vary across subjects.

Paraspinal muscle control in people with osteoporotic vertebral fracture

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Comparing routine neurorehabilitation program with trunk exercises based on Bobath concept in multiple sclerosis: Pilot study

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Cyclic H-Reflex Modulation in Resting Forearm Related to Contractions of Foot Movers, Not to Foot Movement

“…When explicitly manifest, they are characterized by the parallel activation of muscles in different body segments, are scaled with the intensity of the prime movement (Aruin and Latash 1996), and can be reduced or abolished when the biomechanical context is modified (Aruin et al 1998). Further, their timing and spatial distribution may vary when the surrounding conditions or some feature of the movement (e.g., direction) is changed (Aruin and Latash 1995;Nashner and Forssberg 1986). This allows one to imagine that, even when a manifest intervention of the anticipatory postural activities is not required, subthreshold effects may nevertheless take place.…”