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 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. 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 power 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 pedaling a novel ergometer, which has a split axle and a servomotor connected to each axle. The two servomotors are computer-programmed 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: Analysis of the biomechanics of pedaling identified control primitives. Three agonist-antagonist 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 show that interlimb coordinating mechanisms fine-tune bifunctional muscle activity in pedaling, and may apply to other rhythmic lower limb tasks such as walking. Expected Outcome: Computer simulations are being used by us and others to analyze the muscle coordination and the biomechanics of lower limb motor tasks, such as walking in healthy persons and persons with neurological and orthopaedic impairments. The knowledge obtained via computer simulation analysis is virtually unobtainable through experiments alone. These computer simulations will significantly foster the design and development of neurological and musculoskeletal rehabilitation strategies. Funding Source: NIH Funding Status: Funded |
