The interplay of length and force feedback in regulating joint and limb impedance and inter-joint coordination
Author(s)
Govindaraj, Thendral
Advisor(s)
Editor(s)
Collections
Supplementary to:
Permanent Link
Abstract
Neural feedback pathways arise from a variety of sensory receptors. The firing of muscle spindles is related to length and velocity, while Golgi tendon organs measure active contractile force. Understanding the functions of these pathways during voluntary movement is important because they become disrupted in Spinal Cord Injury (SCI) and stroke. Most spindle pathways are relatively localized, but some are inter-joint. These inter-joint
pathways may play a role in regulating whole limb properties. Experiments have shown that force-dependent feedback can be widely distributed and asymmetric between a given
muscle pair. Additionally, force feedback is modulated according to the task and condition, such as slope walking and SCI. Although the muscle-level distributions of force feedback
in the feline hindlimb have been measured under different conditions, it is not known how these distributions regulate limb mechanics (impedance and inter-joint coordination). To
investigate how inter-joint spinal reflex feedback influences joint and limb impedance and inter-joint coordination under locomotion-like conditions, we developed a novel computational
modeling and analysis framework. Our hypothesis was that length and force feedback modulate joint and limb impedance in a task-dependent manner while maintaining
inter-joint coordination.
To address this hypothesis, we developed a set of novel computational models and an
analysis framework. Our first model includes an infinitely thin rod with viscoelastic properties (intrinsic + reflex) incorporated into a single joint, and the analysis framework evaluates
the impedance when a sinusoidal torque is applied to the joint. Using this model and analysis framework, the goal of aim 1 was to investigate the influence of muscle spindle and
Golgi tendon organ feedback on the impedance regulation of a single joint. We found that different combinations of spindle and tendon organ gains can achieve the same impedance,
even with 20% lower intrinsic impedance. In support of the stiffness regulation hypothesis, impedance and internal regulation can be controlled separately because changing the ratio of length to force feedback can modify the impedance without altering the compensation for fatigue.
To test an extension of the stiffness regulation hypothesis to multi-joint systems, we developed a computational model with two infinitely thin rods, intrinsic viscoelastic properties incorporated into two joints, and reflexes represented at the joint level. The analysis framework evaluates the whole limb and joint apparent impedances and inter-joint coordination when a sinusoidal endpoint force is applied to the end of the distal segment. We varied the direction of the endpoint force to simulate different locomotion tasks and combinations of joints. The goal of aims 2 and 3 is to evaluate the influence of inter-joint length and force feedback on the regulation of whole limb impedance and on inter-joint coordination. As hypothesized, inter-joint length and force feedback modulate limb impedance in a
task-dependent manner over part of a functionally relevant range of endpoint force directions, which has implications for rehabilitation after incomplete SCI. The two joint model and analysis framework can provide a template for the control of multi-joint exoskeletons.
The results in this dissertation give insight into how reflex gains are modulated to achieve the impedance required for certain tasks and conditions in all animals with multi segmented limbs.
Sponsor
Date
2024-07-27
Extent
Resource Type
Text
Resource Subtype
Dissertation