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Posture strategies generated by constrained optimization
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-5417-5939
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.

Place, publisher, year, edition, pages
2012. Vol. 45, no 3, 461-468 p.
Keyword [en]
Posture, Multibody system, Static optimization
National Category
Biophysics
Identifiers
URN: urn:nbn:se:kth:diva-25703DOI: 10.1016/j.jbiomech.2011.11.053ISI: 000300863600008Scopus ID: 2-s2.0-84856035585OAI: oai:DiVA.org:kth-25703DiVA: diva2:359535
Funder
Swedish Research Council
Note
QC 20120326Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Human Postures and Movements analysed through Constrained Optimization
Open this publication in new window or tab >>Human Postures and Movements analysed through Constrained Optimization
2009 (English)Licentiate 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.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. viii, 26 p.
Series
Trita-MEK, ISSN 0348-467X ; 2009:06
Keyword
multibody system, optimal control, trajectory optimization, long jump, posture
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-10682 (URN)
Presentation
2009-06-11, Sal E51, Osquars Backe 18, KTH, Stockholm, 10:30 (English)
Opponent
Supervisors
Available from: 2009-06-24 Created: 2009-06-23 Last updated: 2010-10-28Bibliographically approved
2. Simulation of Human Movements through Optimization
Open this publication in new window or tab >>Simulation of Human Movements through Optimization
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
multibody system, human movements, optimal control, trajectory optimization, long jump, posture, rowing, somersault
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-102158 (URN)978-91-7501-472-2 (ISBN)
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

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