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Brock Laschowski, Naser Mehrabi and John McPhee

mathematically represented by 4 ordinary differential equations and 1 algebraic equation (ie, indicative of the model’s kinematic constraints). Kinematic Constraints The experimental kinematics were mathematically optimized to satisfy the kinematic constraints of the multibody biomechanical model. A nonlinear

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L.J. Richard Casius, Maarten F. Bobbert and Arthur J. van Soest

Mathematical modeling and computer simulation play an increasingly important role in the search for answers to questions that cannot be addressed experimentally. One of the biggest challenges in forward simulation of the movements of the musculoskeletal system is finding an optimal control strategy. It is not uncommon for this type of optimization problem that the segment dynamics need to be calculated millions of times. In addition, these calculations typically consume a large part of the CPU time during forward movement simulations. As numerous human movements are two-dimensional (2-D) to a reasonable approximation, it is extremely convenient to have a dedicated, computational efficient method for 2-D movements. In this paper we shall present such a method. The main goal is to show that a systematic approach can be adopted which allows for both automatic formulation and solution of the equations of kinematics and dynamics, and to provide some fundamental insight in the mechanical theory behind forward dynamics problems in general. To illustrate matters, we provide for download an example implementation of the main segment dynamics algorithm, as well as a complete implementation of a model of human sprint cycling.

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Gertjan J.C. Ettema, Steinar Bråten and Maarten F. Bobbert

A ski jumper tries to maintain an aerodynamic position in the in-run during changing environmental forces. The purpose of this study was to analyze the mechanical demands on a ski jumper taking the in-run in a static position. We simulated the in-run in ski jumping with a 4-segment forward dynamic model (foot, leg, thigh, and upper body). The curved path of the in-run was used as kinematic constraint, and drag, lift, and snow friction were incorporated. Drag and snow friction created a forward rotating moment that had to be counteracted by a plantar flexion moment and caused the line of action of the normal force to pass anteriorly to the center of mass continuously. The normal force increased from 0.88G on the first straight to 1.65G in the curve. The required knee joint moment increased more because of an altered center of pressure. During the transition from the straight to the curve there was a rapid forward shift of the center of pressure under the foot, reflecting a short but high angular acceleration. Because unrealistically high rates of change of moment are required, an athlete cannot do this without changing body configuration which reduces the required rate of moment changes.

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Jeffrey J. Chu and Graham E. Caldwell

Studies on shock attenuation during running have induced alterations in impact loading by imposing kinematic constraints, e.g., stride length changes. The role of shock attenuation mechanisms has been shown using mass-spring-damper (MSD) models, with spring stiffness related to impact shock dissipation. The present study altered the magnitude of impact loading by changing downhill surface grade, thus allowing runners to choose their own preferred kinematic patterns. We hypothesized that increasing downhill grade would cause concomitant increases in both impact shock and shock attenuation, and that MSD model stiffness values would reflect these increases. Ten experienced runners ran at 4.17 m/s on a treadmill at surface grades of 0% (level) to 12% downhill. Accelerometers were placed on the tibia and head, and reflective markers were used to register segmental kinematics. An MSD model was used in conjunction with head and tibial accelerations to determine head/arm/trunk center of mass (HATCOM) stiffness (K1), and lower extremity (LEGCOM) stiffness (K2) and damping (C). Participants responded to increases in downhill grade in one of two ways. Group LowSA had lower peak tibial accelerations but greater peak head accelerations than Group HighSA, and thus had lower shock attenuation. LowSA also showed greater joint extension at heelstrike, higher HATCOM heelstrike velocity, reduced K1 stiffness, and decreased damping than HighSA. The differences between groups were exaggerated at the steeper downhill grades. The separate responses may be due to conflicts between the requirements of controlling HATCOM kinematics and shock attenuation. LowSA needed greater joint extension to resist their higher HATCOM heelstrike velocities, but a consequence of this strategy was the reduced ability to attenuate shock with the lower extremity joints during early stance. With lower HATCOM impact velocities, the HighSA runners were able to adopt a strategy that gave more control of shock attenuation, especially at the steepest grades.

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Caterina Pesce, Ilaria Masci, Rosalba Marchetti, Giuseppe Vannozzi and Mirko Schmidt

-0027 10.1123/pes.2013-0027 Stodden , D.F. , Langendorfer , S.J. , Fleisig , G.S. , & Andrews , J.R. ( 2006 a). Kinematic constraints associated with the acquisition of overarm throwing part I: Step and trunk actions . Research Quarterly for Exercise and Sport, 77 , 417 – 427 . Stodden , D

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Danielle Nesbitt, Sergio Molina, Ryan Sacko, Leah E. Robinson, Ali Brian and David Stodden

:10.1080/00336297.2008.10483582 10.1080/00336297.2008.10483582 Stodden , D.F. , Langendorfer , S.J. , Fleisig , G.S. , & Andrews , J.R. ( 2006a ). Kinematic constraints associated with the acquisition of overarm throwing Part I: Step and trunk actions . Research Quarterly for Exercise and

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Jerraco L. Johnson, Mary E. Rudisill, Peter A. Hastie and Julia Sassi

constraints associated with the acquisition of overarm throwing Part I: Step and trunk actions . Research Quarterly for Exercise and Sport, 77 , 417 – 427 . Stodden , D.F. , Langendorfer , S.J. , Fleisig , G.S. , & Andrews , J.R. ( 2006b ). Kinematic constraints associated with the acquisition of

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Yumeng Li, He Wang and Kathy J. Simpson

. 31 Kinematic constraints were then removed, and a forward dynamics simulation was performed with muscles serving as actuators and experimental GRFs applied to replicate the landing motion. A proportional–integral–derivative feedback controller was implemented to calculate each muscle force magnitude

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Sergio L. Molina and David F. Stodden

, 60 ( 2 ), 290 – 306 . doi:10.1080/00336297.2008.10483582 10.1080/00336297.2008.10483582 Stodden , D.F. , Langendorfer , S.J. , Fleisig , G.S. , & Andrews , J.R. ( 2006 ). Kinematic constraints associated with the acquisition of overarm throwing part I: Step and trunk actions . Research

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Michael Ashford, Andrew Abraham and Jamie Poolton

probability information . Perception, 30 ( 2 ), 233 – 252 . PubMed ID: 11296504 doi: 10.1068/p2872 Abernethy , B. , Zawi , K. , & Jackson , R.C. ( 2008 ). Expertise and attunement to kinematic constraints . Perception, 37 ( 6 ), 931 – 948 . PubMed ID: 18686711 doi: 10.1068/p5340 Abraham