Neuromechanical interference of posture on movement: evidence from Alexander technique teachers rising from a chair

TY - JOUR

T1 - Neuromechanical interference of posture on movement

T2 - evidence from Alexander technique teachers rising from a chair

AU - Cacciatore, Timothy W

AU - Mian, Omar S

AU - Peters, Amy

AU - Day, Brian L

N1 - Copyright © 2014 the American Physiological Society.

PY - 2014/8/1

Y1 - 2014/8/1

N2 - While Alexander technique (AT) teachers have been reported to stand up by shifting weight gradually as they incline the trunk forward, healthy untrained (HU) adults appear unable to rise in this way. This study examines the hypothesis that HU have difficulty rising smoothly, and that this difficulty relates to reported differences in postural stiffness between groups. A wide range of movement durations (1-8 s) and anteroposterior foot placements were studied under the instruction to rise at a uniform rate. Before seat-off (SO) there were clear and profound performance differences between groups, particularly for slower movements, that could not be explained by strength differences. For each movement duration, HU used approximately twice the forward center-of-mass (CoM) velocity and vertical feet-loading rate as AT. For slow movements, HU violated task instruction by abruptly speeding up and rapidly shifting weight just before SO. In contrast, AT shifted weight gradually while smoothly advancing the CoM, achieving a more anterior CoM at SO. A neuromechanical model revealed a mechanism whereby stiffness affects standing up by exacerbating a conflict between postural and balance constraints. Thus activating leg extensors to take body weight hinders forward CoM progression toward the feet. HU's abrupt weight shift can be explained by reliance on momentum to stretch stiff leg extensors. AT's smooth rises can be explained by heightened dynamic tone control that reduces leg extensor resistance and improves force transmission across the trunk. Our results suggest postural control shapes movement coordination through a dynamic "postural frame" that affects the resistive behavior of the body.

AB - While Alexander technique (AT) teachers have been reported to stand up by shifting weight gradually as they incline the trunk forward, healthy untrained (HU) adults appear unable to rise in this way. This study examines the hypothesis that HU have difficulty rising smoothly, and that this difficulty relates to reported differences in postural stiffness between groups. A wide range of movement durations (1-8 s) and anteroposterior foot placements were studied under the instruction to rise at a uniform rate. Before seat-off (SO) there were clear and profound performance differences between groups, particularly for slower movements, that could not be explained by strength differences. For each movement duration, HU used approximately twice the forward center-of-mass (CoM) velocity and vertical feet-loading rate as AT. For slow movements, HU violated task instruction by abruptly speeding up and rapidly shifting weight just before SO. In contrast, AT shifted weight gradually while smoothly advancing the CoM, achieving a more anterior CoM at SO. A neuromechanical model revealed a mechanism whereby stiffness affects standing up by exacerbating a conflict between postural and balance constraints. Thus activating leg extensors to take body weight hinders forward CoM progression toward the feet. HU's abrupt weight shift can be explained by reliance on momentum to stretch stiff leg extensors. AT's smooth rises can be explained by heightened dynamic tone control that reduces leg extensor resistance and improves force transmission across the trunk. Our results suggest postural control shapes movement coordination through a dynamic "postural frame" that affects the resistive behavior of the body.

KW - Adult

KW - Aged

KW - Exercise Movement Techniques

KW - Female

KW - Humans

KW - Leg

KW - Male

KW - Middle Aged

KW - Models, Neurological

KW - Movement

KW - Muscle, Skeletal

KW - Postural Balance

KW - Posture

KW - Professional Competence

KW - Torso

U2 - 10.1152/jn.00617.2013

DO - 10.1152/jn.00617.2013

M3 - Article

C2 - 25085609

SN - 0022-3077

VL - 112

SP - 719

EP - 729

JO - Journal of neurophysiology

JF - Journal of neurophysiology

IS - 3

ER -