Investigator: Steven A. Kautz, PhD

Project Staff: Carolynn Patten, PhD PT

Summary: Persons with post-stroke hemiplegia need to improve lower limb function. Lower limb tasks, like standing and walking, depend on the ability of the legs to produce effective forces at the feet. We hypothesize that hemiplegic persons have diminished function because of their inability to activate muscles independently. The objective of this project is to identify coordination deficits by having hemiplegic subjects perform a variety of tasks on a pedaling ergometer. A computer model of the musculoskeletal system applied to pedaling will serve as the framework for relating experimental data to functional significance.

Objective: Computer models of the musculoskeletal system now make it possible to study the motor control of multijoint movements in terms of the mechanical requirements needed to accomplish particular tasks. One of the next great challenges in biomedical engineering will be to apply this technique to help restore function to people with disabilities. It is to be expected that these models will be powerful tools for pinpointing the mechanical implications of central and peripheral nervous system deficits, for designing more effective surgical interventions, and for devising rehabilitation strategies that allow the patient to make optimum use of the function that still remains.

The focus of this proposal is to use computer models in conjunction with experiments to investigate deficits in the neural control of the lower extremity in patients with post-stroke hemiplegia. Hemiplegic stroke patients with lower extremity dysfunction constitute a sizable and growing portion of the rehabilitation patient population. Rehabilitation strategies that were more effective at improving these patients' ability to walk would dramatically improve their quality of life. The long-term objective of the proposed research is to improve lower extremity function in persons with hemiplegia.

Research Plan: Based on previous experience, we believe that these issues can be studied effectively using a servo-motor assisted ergometer-pedaling paradigm that we have developed in the course of our ongoing research. Since pedaling is a constrained movement, its biomechanics can be modeled in a straight forward fashion. However, pedaling is still complex enough to be extremely interesting from a motor control point of view. Like most lower extremity functions, pedaling and walking can be characterized by the activation of multiple muscles to produce a force that is transmitted through the foot to the environment. All the major functions required for successful interaction with the environment can be accomplished on a servo-motor assisted ergometer, including generating isometric force, and performing positive and negative mechanical work. Furthermore, these functions can be decoupled from functions in the non-plegic leg through use of the servo-motor assisted ergometer. Depending on the mechanics of the endpoint-environment interaction, a similar activation of muscles could result in an isometric endpoint force, mechanical work being done by the leg (positive work), or mechanical work being done on the leg by the environment (negative work).

Methodology: Specifically, we propose to use a servo-motor assisted ergometer pedaling paradigm to test the hypothesis that nervous system constraints (inappropriate synergies and interlimb coupling) limit the ability of the hemiplegic person to generate the appropriate endpoint force for a desired function. In order to test this hypothesis, we propose to achieve the following specific aims:

1. Develop a three-dimensional computer simulation model of the musculoskeletal system and the pedalling task to study the inter- and intra-leg coordination responsible for producing endpoint forces to interact with different mechanical loads.

2. Determine how "neural constraints" limit the ability of the hemiplegic person to: generate isometric force in a desired direction, do mechanical work in a desired direction during discrete tasks, and do mechanical work during cyclical tasks.

Findings: Computer simulation analyses has suggested that prolonged excitation of the power-producing muscles is the major factor related to EMG timing abnormalities that impairs the speed of movement in persons with hemiplegia. Experimental data suggest that abnormal interlimb influences substantially affect the coordination of the plegic leg.

Funding Source: Whitaker Foundation

Years: 1996-1999