Identification of Central and Stretch Reflex Contributions to Human Postural Control.

Pouya Amiri,Robert E Kearney

doi:10.1109/tnsre.2021.3057785

Abstract

Human postural control requires continuous modulation of ankle torque to stabilize the upright stance. The torque is generated by two components: active contributions, due to central control and stretch reflex, and passive mechanisms, due to joint intrinsic stiffness. Identifying the contribution of each component is difficult, since their effects appear together, and standing is controlled in closed-loop. This article presents a novel multiple-input, single-output method to identify central and stretch reflex contributions to human postural control. The model uses ankle muscle EMGs as inputs and requires no kinematic data. Application of the method to data from nine subjects during standing while subjected to perturbations of ankle position demonstrated that active torque accounted for 84.0± 5.5% of the ankle torque. The ankle plantar-flexors collectively produced the largest portion of the active torque through central control, with large inter-subject variability in the relative contributions of the individual muscles. In addition, reflex contribution of the plantar-flexors was substantial in half of the subjects, showing its potentially important functional role; finally, intrinsic contributions, estimated as the residual of the model, contributed to 15% of the torque. This study introduces a new method to quantify the contributions of the central and stretch reflex pathways to postural control; the method also provides an estimate of noisy intrinsic torque with significantly increased signal to noise ratio, suitable for identification of intrinsic stiffness in standing. The method can be used in different experimental conditions and requires minimal a-priori assumption regarding the role of different pathways in postural control.

Highlights

D URING standing, the human body resembles an unstable inverted pendulum, subject to internal and external perturbations
The weights in (6), and the poles and zeros in (7) are unknown and must be identified. These were estimated in three steps, using the data from the first trial: 1) Identification of triceps surae (TS) EMG Weights: To determine the weights in (6), we examined a wide range of structures for the transfer function (TF) in (7)
We developed a method to determine central and stretch reflex contributions to ankle torque in standing

Summary

Introduction

D URING standing, the human body resembles an unstable inverted pendulum, subject to internal and external perturbations. The ankle muscles generate corrective forces that resist these perturbations and allow humans to keep their balance . Manuscript received August 31, 2020; revised January 10, 2021; accepted January 30, 2021. Date of publication February 8, 2021; date of current version March 2, 2021.

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Results

Conclusion