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Evaluation of load-sharing and load capacity in force-limited muscle systems
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-5417-5939
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0002-5819-4544
2006 (English)In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259Article in journal (Other academic) Submitted
Abstract [en]

This study had the objective to develop an algorithm for accurate force decomposition in a redundant musculoskeletal system. The hypothesis was that the calculated load-sharing is dependent on the optimality criterion adopted, but also on the magnitude of carried load. The developed algorithm emphasizes that several established optimization techniques can be unified, by identifying and separating the underlying optimization functions and the numerical methods to solve the resulting system. A numerically efficient and easily adaptable solution method is thereby created. In addition, individual capacity values are introduced for the muscles, allowing the evaluation of a magnitude-dependent load-sharing, and a load carrying capacity of the whole system. By modularizing the optimization method, the algorithm can be used as part of larger simulation systems. To illustrate the possibilities of the algorithm, a model of the upper limb is used in a set of demonstrative examples. The results from the examples show how the interactions between synergistic muscles is predicted in different configurations, and at different load levels.

Place, publisher, year, edition, pages
2006.
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-5679OAI: oai:DiVA.org:kth-5679DiVA: diva2:10123
Note
QS 20120316Available from: 2006-05-10 Created: 2006-05-10 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Muscular forces from static optimization
Open this publication in new window or tab >>Muscular forces from static optimization
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

At every joint there is a redundant set of muscle activated during movement or loading of the system. Optimization techniques are needed to evaluate individual forces in every muscle. The objective in this thesis was to use static optimization techniques to calculate individual muscle forces in the human extremities.

A cost function based on a performance criterion of the involved muscular forces was set to be minimized together with constraints on the muscle forces, restraining negative and excessive values. Load-sharing, load capacity and optimal forces of a system can be evaluated, based on a description of the muscle architectural properties, such as moment arm, physiological cross-sectional area, and peak isometric force.

The upper and lower extremities were modelled in two separate studies. The upper extremity was modelled as a two link-segment with fixed configurations. Load-sharing properties in a simplified model were analyzed. In a more complex model of the elbow and shoulder joint system of muscular forces, the overall total loading capacity was evaluated.

A lower limb model was then used and optimal forces during gait were evaluated. Gait analysis was performed with simultaneous electromyography (EMG). Gait kinematics and kinetics were used in the static optimization to evaluate of optimal individual muscle forces. EMG recordings measure muscle activation. The raw EMG data was processed and a linear envelope of the signal was used to view the activation profile. A method described as the EMG-to-force method which scales and transforms subject specific EMG data is used to compare the evaluated optimal forces.

Reasonably good correlation between calculated muscle forces from static optimization and EMG profiles was shown. Also, the possibility to view load-sharing properties of a musculoskeletal system demonstrate a promising complement to traditional motion analysis techniques. However, validation of the accurate muscular forces are needed but not possible.

Future work is focused on adding more accurate settings in the muscle architectural properties such as moment arms and physiological cross-sectional areas. Further perspectives with this mathematic modelling technique include analyzing pathological movement, such as cerebral palsy and rheumatoid arthritis where muscular weakness, pain and joint deformities are common. In these, better understanding of muscular action and function are needed for better treatment.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. x, 38 p.
Series
Trita-MEK, ISSN 0348-467X ; 2006:09
Keyword
movement analysis; muscle forces; static optimization
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-3943 (URN)
Presentation
2006-05-19, Seminarierummet, Teknikringen 8, KTH, Stockholm, 11:30
Opponent
Supervisors
Note
QC 20101116Available from: 2006-05-10 Created: 2006-05-10 Last updated: 2010-11-16Bibliographically approved

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Gutierrez-Farewik, ElenaEriksson, Anders

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