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Finite element modeling reveals complex strain mechanics in the aponeuroses of contracting skeletal muscle.

ABSTRACT: A finite element model was used to investigate the counter-intuitive experimental observation that some regions of the aponeuroses of a loaded and contracting muscle may shorten rather than undergo an expected lengthening. The model confirms the experimental findings and suggests that pennation angle plays a significant role in determining whether regions of the aponeuroses stretch or shorten. A smaller pennation angles (25 degrees ) was accompanied by aponeurosis lengthening whereas a larger pennation angle (47 degrees ) was accompanied by mixed strain effects depending upon location along the length of the aponeurosis. This can be explained by the Poisson effect during muscle contraction and a Mohr's circle analogy. Constant volume constraint requires that fiber cross sectional dimensions increase when a fiber shortens. The opposing influences of these two strains upon the aponeurosis combine in proportion to the pennation angle. Lower pennation angles emphasize the influence of fiber shortening upon the aponeurosis and thus favor aponeurosis compression, whereas higher pennation angles increase the influence of cross sectional changes and therefore favor aponeurosis stretch. The distance separating the aponeuroses was also found to depend upon pennation angle during simulated contractions. Smaller pennation angles favored increased aponeurosis separation larger pennation angles favored decreased separation. These findings caution that measures of the mechanical properties of aponeuroses in intact muscle may be affected by contributions from adjacent muscle fibers and that the influence of muscle fibers on aponeurosis strain will depend upon the fiber pennation angle.

SUBMITTER: Chi SW

PROVIDER: S-EPMC2857665 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature

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Finite element modeling reveals complex strain mechanics in the aponeuroses of contracting skeletal muscle.

Chi Sheng-Wei SW Hodgson John J Chen Jiun-Shyan JS Reggie Edgerton V V Shin David D DD Roiz Ronald A RA Sinha Shantanu S

Journal of biomechanics 20100226 7

A finite element model was used to investigate the counter-intuitive experimental observation that some regions of the aponeuroses of a loaded and contracting muscle may shorten rather than undergo an expected lengthening. The model confirms the experimental findings and suggests that pennation angle plays a significant role in determining whether regions of the aponeuroses stretch or shorten. A smaller pennation angles (25 degrees ) was accompanied by aponeurosis lengthening whereas a larger pe ...[more]

PMID: 20189180

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Project description:Sarcomere lengths and their changes are key determinants of muscle active force production. Recent studies indicate inhomogeneity of sarcomere lengths within the muscle. Studies utilizing magnetic resonance imaging (MRI) analyses for quantifying local muscle tissue strains and diffusion tensor imaging (DTI) analyses allowing for determination of their components along muscle fascicles show that those length changes can be non-uniform. Specifically, two questions arise regarding the muscle's length change heterogeneities along the muscle fiber direction: (1) How can a passively lengthened muscle show shortened regions? (2) How can an isometric contracting muscle show lengthened parts? Using finite element modeling and studying principles of the mechanism of strain heterogeneity along the muscle fiber direction, the aim was to test the following hypothesis: epimuscular myofascial loads can lead locally to strains opposing those elsewhere within the muscle that are determined by the globally imposed conditions. The geometry of the model was defined by the contour of a longitudinal slice of the rat extensor digitorum longus (EDL) muscle belly. Three models were studied: (1) isolated muscle (muscle modeled fully isolated from its surroundings) and models aiming at representing the principles of a muscle in its in vivo context including (2) extramuscularly connected muscle (muscle's connections to non-muscular structures are modeled exclusively) and (3) epimuscularly connected muscle (additionally muscle's connections to neighboring muscle are modeled). Three cases were studied: passive isometric muscle with imposed relative position change (Case I), passive lengthened muscle (Case II), and active isometric muscle with imposed relative position change (Case III). The findings indicated non-uniform strains for all models except for zero strain in model (1) in Case I, but models (2) and (3) also showed strains opposing the imposed effect. Case I: model (3) showed shortened and lengthened sections (up to 35.3%), caused exclusively by imposed relative position change. Case II: models (2) and (3) showed shortened sections (up to 12.7 and 19.5%, respectively) in addition to lengthened sections. Case III: models (2) and (3) showed lengthened sections (up to 5 and 23.4%, respectively) in addition to shortened sections. These effects get more pronounced with stiffer epimuscular connections. Assessments of forces exerted on the muscle by the epimuscular connections showed that such strain heterogeneities are ascribed to epimuscular myofascial loads determined by muscle relative position changes.

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Finite element modeling reveals complex strain mechanics in the aponeuroses of contracting skeletal muscle.

Publications

Finite element modeling reveals complex strain mechanics in the aponeuroses of contracting skeletal muscle.

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