A Link-Segment Model of Upright Human Posture for Analysis of Head-Trunk Coordination

Abstract

Sensory-motor control of upright human posture may be organized in a top-down fashion such that certain head-trunk coordination strategies are employed to optimize visual and/or vestibular sensory inputs. Previous quantitative models of the biomechanics of human posture control have examined the simple case of ankle sway strategy, in which an inverted pendulum model is used, and the somewhat more complicated case of hip sway strategy, in which multisegment, articulated models are used. While these models can be used to quantify the gross dynamics of posture control, they are not sufficiently detailed to analyze head-trunk coordination strategies that may be crucial to understanding its underlying mechanisms. In this paper, we present a biomechanical model of upright human posture that extends an existing four mass, sagittal plane, link-segment model to a five mass model including an independent head link. The new model was developed to analyze segmental body movements during dynamic posturography experiments in order to study head-trunk coordination strategies and their influence on sensory inputs to balance control. It was designed specifically to analyze data collected on the EquiTest™ (NeuroCom International, Clackamas, OR) computerized dynamic posturography system, where the task of maintaining postural equilibrium may be challenged under conditions in which the visual surround, support surface, or both are in motion. The performance of the model was tested by comparing its estimated ground reaction forces to those measured directly by support surface force transducers. We conclude that this model will be a valuable analytical tool in the search for mechanisms of balance control.

Comparison of the ankle, knee, hip, and trunk corrective action shown during single-leg stance on firm, foam, and multiaxial surfaces

“…This information provides assistance to researchers and clinicians deciding which types of support surface and visual conditions are needed to target specific joints during single-leg stance testing and rehabilitation procedures. Although the assumption that the body sways as an inverted pendulum about the ankle during quiet double-leg stance has been widely used, 31 multiple studies 21,[31][32][33] have shown that the body does not move as a rigid segment but rather as a multilink structure. For example, Day et al 21 revealed that, in the sagittal plane, the most angular movement occurred between the trunk and upper leg, independent of stance width.…”

Postural control in healthy adults: Determinants of trunk sway assessed with a chest-worn accelerometer in 12 quiet standing tasks

“…However, some investigators have successfully assessed postural balance through upper-trunk accelerometry [6,34,35]. Indeed, measuring the acceleration of the upper trunk may not only offer better sensitivity to postural response but also yield specific information about trunk dynamics [36–38]. Data obtained by upper-trunk accelerometry are still sparse.…”

Human balancing of an inverted pendulum: position control by small, ballistic‐like, throw and catch movements

“…Gatev et al (1999) showed that ankle mechanisms dominate in the sagittal plane with an almost synchronous sway of body parts. Other authors have used more complex models to represent standing (Jacobs, 1997; Lauk et al 1998; Nicholas et al 1998; Alsonso‐Sanchez & Hochberg, 2000), or have disputed the relevance of the ankle strategy and inverted pendulum model in standing (Bloem et al 2000).…”