Principal Investigator: Felix E. Zajac, PhD Project Staff: Steven A. Kautz, PhD and Richard R. Neptune PhD Project Category: Stroke - 2001 Objective: Walking requires the coordination of many muscles. The lower limbs are also used to propel the body in other locomotor tasks, such as pedaling. This project is to study locomotor tasks to develop a scientific basis for muscle coordination of the lower limbs applicable to the delineation of how pathology affects walking coordination in individuals with orthopaedic or neurologic impairments. Research Plan: Knowledge of muscle coordination of walking emanates in large part from the ability to measure muscle activity and the kinematics and kinetics of the body. Gait laboratories can measure the walking patterns of healthy, and orthopaedic and neurologically impaired individuals. The surgical, medical, and engineering gait-laboratory team interprets these measurements to provide rehabilitation and assess medical outcome. The interpretation of these measurements is based on the ability of the team to infer from past experience how treatment protocols reverse the observed deviations in coordination to provide a more functional gait. This project is to develop a computer-based scientific foundation of walking that will serve as a basis for the systematic assessment, treatment, and rehabilitation of individuals with dysfunctional gait. Computer models of the healthy musculoskeletal system will be the cornerstone for the generation of simulations of walking by healthy individuals. The simulations will be used to understand how muscles work together to move the legs and trunk at each instant in the gait cycle. A computer algorithm will find the muscle excitations that, when applied to the musculoskeletal model, will produce a simulation that best replicates published gait laboratory measurements of healthy walking individuals. A set of simulations will be generated to understand how changes in the muscle excitation pattern, body weight and height, and other musculoskeletal features affect walking behavior. Finally, simulations will be generated to replicate the walking behavior of individuals with walking impairments. These simulations will be analyzed to demonstrate how this computer-based approach can quantify the precise functional effects of treatments on gait, including muscle coordination. Work Accomplished: A computer model of the musculoskeletal system applicable to simulations of the complete gait cycle has been developed. Foot/ground contact, an important feature of any model of stance, is modeled by 30 viscoelastic elements. Each leg is modeled by 14 muscles and 3 rigid bodies (thigh, shank, and foot). One rigid body models the torso, head, and arms. Simulations to understand forward propulsion and body support in walking by healthy individuals at a nominal gait velocity have been generated. Analyses indicate that the uniarticular and biarticular plantarflexors have different roles in forward progression even though each supports the body in single leg support through preswing to toe-off. The uniarticular plantarflexors (e.g., soleus) accelerate the trunk forward and the biarticular plantaflexors (e.g., gastrocnemii) accelerate the leg forward. Expected Outcome: With computer models and simulations as a scientific approach and basis to understand gait, a foundation will have been established for the design of optimal strategies for restoring ambulation to individuals with neurologic and orthopaedic impairments. Such a foundation is virtually unobtainable through gait laboratory measurements alone because of the complex mechanics of the musculoskeletal system. Funding Source: VA RR&D Funding Status: Funded |
