title: An analysis of the sources of musculoskeletal system impedance.
abstract: When antagonistic muscles co-contract, the impedance of musculoskeletal systems to applied loads is known to increase. In this paper a physiologically-based, higher-order, nonlinear antagonistic muscle-joint model is utilized to clarify the sources of impedance modulation during a variety of tasks, ranging from resisting transient loads to holding steady loads to making fast movements in unpredictable surroundings. It is shown that impedance modulation occurs automatically as a function of the specific operating ranges utilized during a given task by each of four different muscle-joint mechanical relations. The relative contribution of each relation depends on the type of task, with impedance during quasi-static conditions sensitive to muscle tension-length and sometimes joint parallel elastic properties and during dynamic tasks dominated by the series element and muscle force-velocity properties. Elimination of any of these causes a decrease in built-in biomechanical capabilities. These findings raise questions concerning past theories on stiffness-impedance modulation which appear to underestimate the role of inherent biomechanical properties.
authors.affiliation: Bioengineering Program, University of California, Berkeley.
authors.forename: J
authors.initials: J
authors.lastname: Winters
authors.forename: L
authors.initials: L
authors.lastname: Stark
authors.forename: A H
authors.initials: AH
authors.lastname: Seif-Naraghi
mesh_terms: D001696:Biomechanical Phenomena; D005246:Feedback; D006801:Humans; D007596:Joints / Q000502:physiology*; D008954:Models, Biological; D009068:Movement; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D011187:Posture