Citation

Engelhart D, Pasma JH, Schouten AC, Aarts RGKM, Meskers CG, Maier AB, van der Kooij H. J. Neurophysiol. 2015; 115(3): 1422-1435.

Affiliation

Biomechanical Engineering, University of Twente.

Copyright

(Copyright © 2015, American Physiological Society)

DOI

10.1152/jn.00030.2015

PMID

26719084

Abstract

Standing balance requires multi-joint coordination between the ankles and hips. We investigated how humans adapt their multi-joint coordination to adjust to various conditions and whether the adaptation differed between healthy young participants and healthy elderly. Balance was disturbed by push/pull rods, applying two continuous and independent force disturbances at the hip level and between the shoulder blades. In addition, external force fields were applied, represented by an external stiffness at the hip, (de)stabilizing the participants' balance. . With multivariate-closed-loop system-identification techniques a description of the neuromuscular control mechanisms were obtained from the corrective joint torques as a response to body sway, represented by Frequency Response Functions (FRFs). Model fits on the FRFs resulted in an estimation of time delays, intrinsic stiffness, reflexive stiffness and damping, of the ankle and hip. Elderly generated similar corrective joint torques but had reduced body sway compared to younger participants, which corresponded to the increased FRF magnitude with age. When a force field was applied, all participants adapted their neuromuscular control actions around the ankles, expressed in a change of FRF magnitude. However, the elderly adapted less compared to the young participants. Model fits on the FRFs showed that elderly had higher intrinsic and reflexive stiffness of the ankle, together with higher time delays of the hip. Furthermore, the elderly adapted their reflexive stiffness around the ankle joint less, compared to young participants. These results imply that elderly were stiffer and were less able to adapt to external force fields.

Language: en