Anticipatory Postural Adjustments and kinematic arm features when postural stability is manipulated.

Bianca Callegari,Cesar Ferreira Amorim,Givago Da Silva Souza,France Mourey,Ghislain Saunier,Gizele Cristina Da Silva Almeida,Thierry Pozzo,Manuela Brito Duarte

doi:10.7717/peerj.4309

Abstract

Beyond the classical paradigm that presents the Anticipatory Postural Adjustments (APAs) as a manner to create forces that counteract disturbances arising from the moving segment during a pointing task, there is a controversial discussion about the role APAs to facilitate the movement and perform a task accurately. In addition, arm kinematics features are classically used to infer the content of motor planning for the execution and the control of arm movements. The present study aimed to disentangle the conflicting role of APAs during an arm-pointing task in which the subjects reach a central diode that suddenly turns on, while their postural stability was manipulated. Three postures were applied: Standing (Up), Sit without feet support (SitUnsup) and Sit with feet support (SitSup). We found that challenging postural stability induced an increase of the reaction time and movement duration (observed for the SitUnsup compared to SitSUp and Up) as well as modified the upper-limb velocity profile. Indeed, a greater max velocity and a shorter deceleration time were observed under the highest stability (SitSup). Thus, these Kinematics features reflect less challenging task and simple motor plan when the body is stabilized. Concerning the APAs, we observed the presence of them independently of the postural stability. Such a result strongly suggests that APAs act to facilitate the limb movement and to counteract perturbation forces. In conclusion, the degree of stability seems particularly tuned to the motor planning of the upper-limb during a pointing task whereas the postural chain (sitting vs. standing) was also determinant for APAs.

Highlights

Postural perturbations induced by fast arm movements in a standing condition were widely studied and generally displace the body’s center of mass (COM) causing a disruption ofHow to cite this article Callegari et al (2018), Anticipatory Postural Adjustments and kinematic arm features when postural stability is manipulated
In this paper we propose to contribute to this controversial issue by studying anticipatory postural adjustments (APAs) in a stable posture, where equilibrium control is minimized and the APA may be more related to the task performance
If APA serves the preparation for forthcoming upper limb movement to perform the task accurately, one could expect the presence of similar APAs patterns independently of the equilibrium constraint

Summary

INTRODUCTION

Postural perturbations induced by fast arm movements in a standing condition were widely studied and generally displace the body’s center of mass (COM) causing a disruption of. It is accepted that anticipatory postural adjustments (APAs) begin before the limb upward movement taking place to counteract the expected mechanical effects of the focal perturbation in a feedforward way (Moore et al, 1992; Santos, Kanekar & Aruin, 2010) Authors suggest that they are generated at a high level of the central nervous system (CNS) promoting earlier changes in the activity of the postural muscles in order to compensate for a potential shift in the COM (Sijper & Latash, 2000; Yoshida et al, 2008). If APA serves the preparation for forthcoming upper limb movement (i.e., in order to accelerate the center of mass) to perform the task accurately, one could expect the presence of similar APAs patterns independently of the equilibrium constraint

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION

CONCLUSION