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Simulation of Human Movements through Optimization
KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
2012 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , x, 48 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:15
Keyword [en]
multibody system, human movements, optimal control, trajectory optimization, long jump, posture, rowing, somersault
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-102158ISBN: 978-91-7501-472-2 (print)OAI: oai:DiVA.org:kth-102158DiVA: diva2:551131
Public defence
2012-09-28, V2, Teknikringen 76, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20120910

Available from: 2012-09-10 Created: 2012-09-10 Last updated: 2012-09-13Bibliographically approved
List of papers
1. Posture strategies generated by constrained optimization
Open this publication in new window or tab >>Posture strategies generated by constrained optimization
2012 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 45, no 3, 461-468 p.Article in journal (Refereed) Published
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.

Keyword
Posture, Multibody system, Static optimization
National Category
Biophysics
Identifiers
urn:nbn:se:kth:diva-25703 (URN)10.1016/j.jbiomech.2011.11.053 (DOI)000300863600008 ()2-s2.0-84856035585 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20120326Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12Bibliographically approved
2. Movement optimization of multibody system subjected to contact constraint with application to long jump
Open this publication in new window or tab >>Movement optimization of multibody system subjected to contact constraint with application to long jump
(English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380Article in journal (Other academic) Submitted
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.

National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-25705 (URN)
Note

QS 20120315

Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12Bibliographically approved
3. Free-time optimization of targeted movements based on temporal FE approximation
Open this publication in new window or tab >>Free-time optimization of targeted movements based on temporal FE approximation
2010 (English)In: Proc. CST 2010, 2010Conference paper, Published paper (Refereed)
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-72784 (URN)
Conference
CST 2010, The Tenth International Conference on Computational Structures Technology. Valencia, Spain. 14-17 September 2010
Funder
Swedish Research Council
Note
QC 20120425Available from: 2012-02-01 Created: 2012-02-01 Last updated: 2012-09-10Bibliographically approved
4. Optimization of multiple phase human movements
Open this publication in new window or tab >>Optimization of multiple phase human movements
(English)In: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272XArticle in journal (Other academic) Submitted
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.

National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-91372 (URN)
Funder
Swedish Research Council
Note

QS 2012

Available from: 2012-03-13 Created: 2012-03-13 Last updated: 2017-12-07Bibliographically approved
5. Simulation of rowing in an optimization context
Open this publication in new window or tab >>Simulation of rowing in an optimization context
2014 (English)In: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 32, no 3, 337-356 p.Article in journal (Refereed) Published
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.

Keyword
Optimal control, Biomechanics, Boat-oar-water interaction, Multiple phase optimization
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-102167 (URN)10.1007/s11044-013-9384-5 (DOI)000341865400004 ()2-s2.0-84920257629 (Scopus ID)
Funder
Swedish National Centre for Research in SportsSwedish Research Council
Note

QC 20141021. Updated from submitted to published.

Available from: 2012-09-10 Created: 2012-09-10 Last updated: 2017-12-07Bibliographically approved

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