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Muscular force production during non-isometric contractions: Towards numerical muscle modeling
KTH, School of Engineering Sciences (SCI), Mechanics. (Structural Mechanics)
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The main objective of the study was to investigate skeletal muscle force production during isometric contractions, active muscle stretches and shortenings. The motivation behind this work is to improve the dominant model of muscle contraction force generation based on the theories of Hill. The effect of force modification was observed after concentric and eccentric contractions and also stretch-shortening cycles. It has been shown that this force modification is not related to lengthening/shortening velocity, and the steady-state force after non-isometric contractions can be well described by initial isometric force and mechanical work performed by and on the muscle during length variations. The time constants calculated for isometric force redevelopment appeared to be in certain relations with those for initial isometric force development, an observation which extended our basis for ongoing muscle modeling. The main method of the project consists in two extensive series of experiments on mouse skeletal muscles. Analysis of the first series of experiments, concentric contractions, with an emphasis on the force depression has been presented in Paper 1. Paper 2 is based on contractions with various stretches and shortenings as well as their combination, force modification and its predictor are the quantities of interest. The third part of the project is also based on the second series of experiments. Timing aspects of the force production were calculated there.

Place, publisher, year, edition, pages
Stockholm: Universitetsservice US-AB , 2009. , x, 42 p.
Series
Trita-MEK, ISSN 0348-467X ; 2009:07
Keyword [en]
Mouse skeletal muscle. Transient-length contractions. Muscular force. Force modification. History effect. Muscle modelling.
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-10672OAI: oai:DiVA.org:kth-10672DiVA: diva2:224286
Presentation
2009-06-11, E51, KTH, Osquars backe 14, Stockholm, 13:30 (English)
Opponent
Supervisors
Note
QC 20120209Available from: 2009-06-22 Created: 2009-06-17 Last updated: 2012-02-09Bibliographically approved
List of papers
1. Muscular force production after concentric contraction
Open this publication in new window or tab >>Muscular force production after concentric contraction
2008 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 41, no 11, 2422-2429 p.Article in journal (Refereed) Published
Abstract [en]

The steady-state force following active shortening does not reach the maximum isometric force associated with the final length. Isolated extensor digitorum longus and soleus muscles from mice (NMRI strain) were used to investigate the force produced by a muscle, and some parameters hypothetically influencing this shortening-induced force depression. The muscles were pre-stimulated at fixed length, shortened and then held isometrically to give maximum post-shortening forces, before de-stimulation. The shortening magnitude was 0.18. 0.36 or 0.72 mm (about 2-7% of optimal length), time of shortening was chosen as 0.03, 0.06 and 0.12 s, and final length as +0.72. 0 and -0.72mm, related to optimal length. The mechanical work during active shortening was evaluated by integrating the product of force and shortening velocity over the shortening period. The results show a positive correlation between the force depression and the mechanical work. whereas the force depression was not correlated to the velocity of shortening. Depression of the passive force component was also observed following all stimulations. Experiments show that the fully stimulated redevelopment of isometric force following concentric contraction follows a time function similar to the creation of force when isometric muscle is initially stimulated. The conclusion is that the isometric force development after active shortening can be well described by an asymptotic force which is decided by the produced work, and the initial isometric time constant.

Keyword
mouse muscles, concentric contractions, force depression, history, dependence, muscular work, cat soleus muscle, skeletal-muscle, length relationship, isometric, force, descending-limb, frog-muscle, depression, enhancement, stretch, relaxation
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-17816 (URN)10.1016/j.jbiomech.2008.05.019 (DOI)000259129000012 ()2-s2.0-48149107349 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Mechanical work as predictor of force enhancement and force depression
Open this publication in new window or tab >>Mechanical work as predictor of force enhancement and force depression
2009 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 42, no 11, 1628-1634 p.Article in journal (Refereed) Published
Abstract [en]

The steady-state force following active muscle shortening or stretch differs from the maximum isometric force associated with the final length. This phenomenon proves that the isometric force production is not only dependent on current muscle length and length time derivative, but depends on the preceding contraction history. Isolated extensor digitorum longus and soleus muscles from mice (NMRI strain) were used to investigate the force produced by a muscle, and some parameters hypothetically influencing this history-dependent force modification. The muscles were pre-stimulated at a fixed length, then different stretch/shortening episodes were introduced, whereafter changes of the active force were recorded while the muscles were held isometrically to approach a steady-state force before de-stimulation. The mechanical work during active stretch and shortening was evaluated by integrating the product of force and ramp velocity over the length-varying period. The results show a negative linear correlation between the force modification and the mechanical work produced on or by the muscle, continuous between shortening and stretch. A corresponding modification of the passive force component following each stimulation was also observed. The conclusion is that the isometric force attained after stretch or shortening is well described by an asymptotic force which is determined by the mechanical work.

Keyword
Mouse skeletal muscles, Transient-length contractions, Stretch-shortening cycle, Force depression, Force enhancement, History, dependence, Muscular work, frog-muscle fibers, cat soleus muscle, skeletal-muscle, length, relationship, isometric force, descending-limb, stretch, tension, simulations, contraction
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-18709 (URN)10.1016/j.jbiomech.2009.04.028 (DOI)000269269800009 ()19486981 (PubMedID)2-s2.0-67651155777 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved

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