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The purpose of this study was to investigate, theoretically, to what extent muscle properties could contribute to recovery from perturbations during locomotion. Four models with different actuator properties were created: the FLVT model, which encompassed force-length (FL) and force-velocity (FV) characteristics of human muscles as well as muscle stimulation inputs as functions of time (T); the FLT model, which had muscles without force-velocity characteristics; the FVT model, which had muscles without specific force-length characteristics; and the MT model, which had no muscles but was driven by joint moments (M) as a function of time. Each model was exposed to static and dynamic perturbations and its response was examined. FLVT showed good resistance to both static and dynamic perturbations. FLT was resistant to static perturbation but could not counteract dynamic perturbation, whereas the opposite was found for FVT. MT could not counteract either of the perturbations. Based on the results of the simulations, skeletal muscle force-length-velocity properties, although interactively complex, contribute substantially to the dynamic stability of the musculoskeletal system.
Karin G.M. Gemtsen was with the Department of Medical Science and the Human Performance Laboratory, University of Calgary, AB, at the time of the study. Anton J. van den Bogert was with the Human Performance Laboratory, Manuel Hulliger is with the Department of Clinical Neurosciences, and Ronald F. Zernicke is with the Human Performance Laboratory and the Departments of Surgery and Mechanical and Civil Engineering, the University of Calgary. Direct correspondence to Karin G.M. Gerritsen, Department of Exercise Science and Physical Education, Arizona state University, Box 870404, Tempe, AZ 85287-0404.