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  • 1. Bartonek, Asa
    et al.
    Lidbeck, Cecilia M.
    Pettersson, Robert
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Weidenhielm, Eva Brostrom
    Eriksson, Marie
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Influence of heel lifts during standing in children with motor disorders2011In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 34, no 3, p. 426-431Article in journal (Refereed)
    Abstract [en]

    Heel wedges may influence standing posture but how and to what extent are unknown. Thirty-two children with motor disorders - 16 with arthrogryposis multiplex congenita (AMC) and 16 with cerebral palsy (CP) - and 19 control children underwent a three-dimensional motion analysis. Unassisted standing during 20s with shoes only and with heel lifts of 10,20 and 30 mm heights was recorded in a randomized order. The more weight-bearing limb or the right limb was chosen for analysis. In both the AMC and CP groups, significant changes were seen between various heel lifts in ankle, knee and pelvis, and in the control group in the ankle only. Between orthosis and non-orthosis users significant differences were seen between different heel lift conditions in ankle, knee and trunk in the AMC group and in the ankle in the CP group. Pelvis position changed toward less anterior tilt with increasing heel height, but led to increasing knee flexion in most of the children, except for the AMC Non-Ort group. Children with AMC and CP represent different motor disorders, but the heel wedges had a similar influence on pelvis, hip and knee positions in all children with CP and in the AMC orthosis users. A challenge is to apply heel heights adequate to each individual's orthopaedic and neurologic conditions to improve biomechanical alignment with respect to all body segments.

  • 2.
    Pettersson, Robert
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Human Postures and Movements analysed through Constrained Optimization2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Constrained optimization is used to derive human postures and movements. In the first study a static 3D model with 30 muscle groups is used to analyse postures. The activation levels of these muscles are minimized in order to represent the individual's choice of posture. Subject specific data in terms of anthropometry, strength and orthopedic aids serve as input. The aim is to study effects from orthopedic treatment and altered abilities of the subject. Initial validation shows qualitative agreement of posture strategies but further details about passive stiffness and anthropometry are needed, especially to predict pelvis orientation. In the second application, the athletic long jump, a problem formulation is developed to find optimal movements of a multibody system when subjected to contact. The model was based on rigid links, joint actuators and a wobbling mass. The contact to the ground was modelled as a spring-damper system with tuned properties. The movement in the degrees of freedom representing physical joints was described over contact time through two fifth-order polynomials, with a variable transition time, while the motion in the degrees of freedom of contact and wobbling mass was integrated forwards in time, as a consequence. Muscle activation variables were then optimized in order to maximize ballistic flight distance. The optimization determined contact time, end configuration, activation and interaction with the ground from an initial configuration. The results from optimization show a reasonable agreement with experimentally recorded jumps, but individual recordings and measurements are needed for more precise conclusions.

     

  • 3.
    Pettersson, Robert
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Simulation of Human Movements through Optimization2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Optimization has been used to simulate human neural control and resulting movement patterns. The short term aim was to develop the methodology required for solving the movement optimization problem often arising when modelling human movements. A long term aim is the contribution to increased knowledge about various human movements, wherein postures is one specific case. Simulation tools can give valuable information to improve orthopeadic treatments and technique for training and performance in sports. In one study a static 3D model with 30 muscle groups was used to analyse postures. The activation levels of these muscles are minimized in order to represent the individual’s choice of posture. Subject specific data in terms of anthropometry, strength and orthopedic aids serve as input. The specific aim of this part was to study effects from orthopedic treatment and altered abilities of the subject. Initial validation shows qualitative agreement of posture strategies but further details about passive stiffness and anthropometry are needed, especially to predict pelvis orientation. Four studies dealt with movement optimization. The main methodological advance was to introduce contact constraints to the movement optimization. A freetime multiple phase formulation was derived to be able to analyse movements where different constraints and degrees of freedom are present in subsequent phases of the movements. The athletic long jump, a two foot high jump, a backward somersault and rowing were used as applications with their different need of formulation. Maximum performance as well as least effort cost functions have been explored. Even though it has been a secondary aim in this work the results show reasonable agreement to expected movements in reality. Case specific subject properties and inclusion of muscle dynamics are required to draw conclusions about improvements in the sport activity, respectively.

  • 4.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Bartonek, Å.
    Gutierrez-Farewik, Elena
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Posture strategies generated by constrained optimization2012In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 45, no 3, p. 461-468Article in journal (Refereed)
    Abstract [en]

    For people with motion disorders, posture can impact fatigue, discomfort or deformities in the long term. Orthopedic treatments such as orthoses or orthopedic surgeries which change geometric properties can improve posture in these individuals. In this study, a model has been created to study posture strategies in such situations. A 3D mechanical model consisting of eight rigid segments and 30 muscle groups is used in which varying moment arms along the ranges of motion and biarticular muscles are considered. The method is based on static optimization, both to solve the load sharing in the muscle system and to choose posture strategy. The optimization computes the specific posture with minimal required effort (level of muscle activations), while fulfilling constraints containing subject specific ranges of motion, muscle strength/weakness and external support if present. Anthropometry and strength were scaled to each individual, based on reported pediatric anthropometry and strength values, combined with each individual's physical assessment. A control group of 10 able-bodied subjects as well as three subjects with motion disorders were studied, and simulated posture was compared with experimental data. The simulation showed reasonable to good agreement and ability to predict the effect of motion disorders and of external support. An example of application in parameter studies was also presented wherein ankle orthosis angles were varied. The model allows the user to study muscle activity at the muscle group level, position of center of mass and moments at joints in various situations.

  • 5.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Movement optimization of multibody system subjected to contact constraint with application to long jumpIn: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380Article in journal (Other academic)
    Abstract [en]

    Optimization is a useful method to study control in biomechanical systems. At the same time the optimization limits and requires consideration of computational cost, degrees of freedom and sensitivity of constraints. Here the athletic long jump has been studied as a multibody system, seeking an optimal take-off technique. The model was based on rigid links, joint actuators and a wobbling mass. The contact to the ground was modelled as a spring-damper system with tuned properties. The movement in the degrees of freedom representing physical joints was described over contact time through two fifth-order polynomials, with a variable transition time, while the motion in the degrees of freedom of contact and wobbling mass was integrated forward in time, as a consequence. Muscle activation variables were then optimized in order to maximize ballistic flight distance. The optimization determined contact time, end configuration, activation and interaction with the ground from an initial configuration. The simulation used initial velocities from recorded jumps(Athens,Muraki) and anatomical data from referred experiments were complemented by assumed reasonable data. A sensitivity study was performed for important basic parameters. The results from optimization show a reasonable agreement with experimentally recorded jumps.

  • 6.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Free-time optimization of targeted movements based on temporal FE approximation2010In: Proc. CST 2010, 2010Conference paper (Refereed)
  • 7.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Free-time optimization of targeted movements based on temporal finite element approximation2010In: Proceedings of the Tenth International Conference on Computational Structures Technology, Civil-Comp Ltd , 2010, Vol. 93Conference paper (Refereed)
    Abstract [en]

    Previous work by the authors has shown that temporal finite element approximations can be used for the representation of targeted optimal control problems, and that a weak equilibrium formulation leads to robust and efficient simulations. A free-time formulation is now introduced to increase the degree of freedom in finding optimal movement. The timescale parameter in relation to the objective function is discussed and verified by numerical examples. For movements with partial contact multiple phases with different mechanical properties are included. The free-time formulation allows these phases to be determined by the optimization. A three-phase two-foot high jump is simulated where the movement optimization finds a prior motion preparing for the subsequent phases with different mechanical properties.

  • 8.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimisation of multiple phase human movements2013In: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 30, no 4, p. 461-484Article in journal (Refereed)
    Abstract [en]

    When simulating human movements it is frequently desirable to optimise multiple phase movements where the phases represent, e.g., different contact conditions. The different constraints are usually acting in parts of the movements and their time durations are in most cases unknown. Therefore a multiple phase free-time optimisation method is formulated in this work, with phase times included as variables. Through a temporal finite element approach, a discrete representation is derived and a nonlinear optimisation algorithm solves for the rather high number of variables (similar to 6000) and constraints (similar to 15000) in the presented numerical problem. A four degrees of freedom test problem, representing a standing high jump, is solved in order to test some basic aspects. A more realistic problem shows its performance in its intended applications, biomechanical simulations. This is a sagittal eight degrees of freedom model for a human backward somersault, including preparing movement, flight phase and landing. The numerical performance as well as some application specific results are discussed. The method description is general and applicable to other movements in its presented format.

  • 9.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Optimization of multiple phase human movementsIn: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272XArticle in journal (Other academic)
    Abstract [en]

    When simulating human movements it is frequently desirable to optimize multiple phase movements where the phases represent, e.g., different contact conditions. The different constraints are usually acting in parts of the movements and their time durations are in most cases unknown. Therefore a multiple phase free-time optimization method is formulated in this work, with phase times included as variables. Through a temporal finite element approach, a discrete representation is derived and a nonlinear optimization algorithm solves for the rather high number of variables (∼ 6000) and constraints (∼ 15000) in the presented numerical problem. The method is applied to a test problem and a more realistic problem in order to test some basic aspects as well as to see its performance in its intended applications, biomechanical simulations. First a four degrees of freedom test problem, representing a standing high jump, is solved. Then a sagittal eight degrees of freedom model is used with application to a human backward somersault, including preparing movement, flight phase and landing. The numerical performance as well as some application specific results are discussed. The method description is general and applicable to other movements in its presented format.

  • 10.
    Pettersson, Robert
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nordmark, Arne
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Simulation of rowing in an optimization context2014In: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 32, no 3, p. 337-356Article in journal (Refereed)
    Abstract [en]

    Competitive rowing requires efforts close to the physiological limits, where oxygen consumption is one main aspect. The rowing event also incorporates interactions between the rower, the boat and oars, and water. When the intention is to improve the performance, all these properties make the sport interesting from a scientific point of view, as the many variables influencing the performance form a complex optimization problem. Our aim was to formulate the rowing event as an optimization problem where the movement and forces are completely determined by the optimization, giving at least qualitative indications on good performance. A mechanical model of rigid links was used to represent rower, boat and oars. A multiple phase cyclic movement was simulated where catch slip, driving phase, release slip and recovery were modeled. For this simplified model, we demonstrate the influence of the stated mathematical cost function as well as a parameter study where the optimal performance is related to the planned average boat velocity. The results show qualitatively good resemblance to expected movements for the rowing event. An energy loss model in combination with case specific properties of rower capacities, boat properties, and rigging was required to draw qualitative practical conclusions about the rowing technique.

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