Principal Investigator: Felix E. Zajac, PhD Project Staff: Steven A. Kautz, PhD; Richard R. Neptune PhD; H.F. Machiel Van der Loos, PhD; and Carolynn Patten, PhD PT Project Category: Stroke - 2001 Objective: Computer models, computer simulations of motor tasks, kinesiological and biomechanical measurements, are to be used to understand muscle coordination of lower limb movement in humans. With computer models as a basis, such understanding provides the foundation for the design of optimal strategies for restoring ambulation to persons with neurologic impairments. Research Plan: A generic computer model of the lower extremities, based on the laws of rigid body mechanics, the anatomical properties of the musculoskeletal system, the architectural design of the musculotendinous system, and muscle dynamics, was developed to generate computer simulations of lower limb motor tasks. The model has been validated since simulations compare favorably with kinesiological and biomechanical measurements obtained during standing and walking. The model has been used to understand how muscles work together to accelerate the limb segments, and produce and deliver energy so lower limb tasks can be executed well. Pedaling, because it is particularly suited to experimental inquiry and yet contains many important features of locomotor tasks, will now be used to “dissect” apart the basic sensorimotor mechanisms of coordination. Muscle excitations, pedal reaction forces, and crank and pedal kinematics are recorded from subjects who pedal. Subjects pedal a novel ergometer, which has a split axle and a servomotor connected to each axle. The two servomotors are computerprogrammed controlled so that the motion of one crank and the forces generated by one leg can affect, or not, the motion of or forces accelerating the other crank. Computer simulations of these various pedaling tasks, which are generated to replicate the experimental data, are used to understand uni- and bi-articular muscle coordination in each leg, and how sensorimotor control of one leg affects the control of the other. Work Accomplished: Control primitives were identified by analyzing the biomechanics of pedaling. Three agonistantagonist primitive pairs control coordination of each leg, where the two primitives of each pair alternate with each other in the crank cycle and, in bicycle pedaling, with their counterparts in the other leg. Experiments, where subjects pedal the novel apparatus, showed that the generation of the pedaling pattern is inherently bilateral. Thus, the generation of the motor output in one leg, especially to biarticular muscles, even in a unilateral task, is influenced by the sensorimotor state of the other leg. These results suggest that the interlimb neural pathways are critical to the control of bifunctional muscles. Expected Outcome: The computer models under development are being used by us and others to understand how specific musculoskeletal and sensorimotor control properties impact muscle coordination. The knowledge obtained via computer simulations of motor tasks is virtually unobtainable through experimental trials alone. Thus, these computer models and simulations will significantly foster the design and development of new neurological and musculoskeletal rehabilitation strategies. Funding Source: NIH Funding Status: Funded |
