Principal Investigator: Felix E. Zajac, PhD Project Staff: Steven A. Kautz, PhD; Richard R. Neptune, PhD; Machiel
Van der Loos, PhD, and Carolynn Patten, PhD, PT Project Category: Stroke - 2003 Objective: Computer models, computer simulations of motor tasks, kinesiological and biomechanical measurements, were used to understand muscle coordination of human leg movement. Research Plan: A generic computer model of the legs, 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 motor tasks. The model was validated by comparing simulation-generated data with kinesiological and biomechanical measurements obtained during pedaling and walking. The model was used to understand how muscles work together to accelerate the limb segments and produce and deliver energy to the body. Pedaling, because it was particularly suited to experimental inquiry and yet contains many important features of locomotor tasks, was emphasized because the discovery of basic sensorimotor mechanisms of coordination could be found and the computer model validated. Work Accomplished: Analysis of the computer simulations of pedaling identified three control primitives. Only three agonist-antagonist primitive pairs are needed to control coordination of each leg, where the two primitives of each pair alternate with each other in the crank cycle and with their counterparts in the other leg. Interlimb neural pathways were shown to exist onto the primitives controlling the contralateral thigh bifunctional muscles (i.e., rectus femoris; hamstrings). Analysis of simulations of walking at 1.5 m/s indicated that in single-leg stance both the uniarticular and biiarticular plantar flexors support the leg and trunk. The plantar flexors were also found to accelerate the body forward in late stance, with the uniarticulars accelerating the trunk and the biiarticulars the leg. In mid stance, the uniarticular and biarticular plantar flexors have opposite effects on the leg and trunk, with the uniarticulars accelerating the trunk but decelerating the leg. The summed effect of the plantar flexors in mid stance is, therefore, to provide support of the body so the trunk and the leg can progress forward by the interchange of potential energy with kinetic energy of each segment. The hamstrings and the uniarticular knee and hip muscles were found to provide critical support of the body in early stance as the contralateral leg prepared to leave the ground. Expected Outcome: The computer models developed are being used 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 |
