Dissertation/Thesis Abstract

Quantifying structural and activation-dependent contributions to short-range stiffness of skeletal muscles
by Cui, Lei, Ph.D., Northwestern University, 2007, 128; 3284317
Abstract (Summary)

Short-range stiffness (SRS) of a skeletal muscle describes the muscle's capability to resist external perturbations before the nervous system can intervene. Knowledge of the SRS of individual muscles is critical in understanding their contributions to single joint stiffness and whole limb stability. While the dependence of SRS on muscle force and passive connective tissues has been studied in the literature, it remains unclear how structural and activation-dependent components each contribute to whole muscle SRS. The primary goal of this dissertation is to quantify these contributions and identify the most important muscle parameters for estimating the SRS of individual muscles.

Firstly, this dissertation examined the effect of motor unit composition and firing rate on whole muscle SRS. This effect was quantified by comparing the SRS-force relationship of the heterogeneous feline medial gastrocnemius (MG) muscle between natural activation and electrical stimulation. It was found that motor unit types and their recruitment have little impact on the SRS-force relationship, suggesting that muscle architecture and material properties of tendinous structures may be more important for determining whole muscle SRS.

Secondly, it was examined whether the SRS of an individual muscle as a function of force can be estimated solely from its anatomical parameters. This was done by comparing the SRS-force estimates of such an anatomical model with experimental results in six architecturally different muscles. Except for the extensor digitorum longus (EDL), the model predicted the SRS-force relationship within measurement errors. The modeling results suggest that EDL tendon may have a higher elastic modulus.

Finally, the tendon stress-strain relationships of EDL, MG and tibialis anterior (TA) were measured and compared during isometric contractions in situ. It was found that EDL tendon indeed has a higher tangential modulus beyond 1% strain. In addition, the MG tendon was found to have a larger peak strain than EDL and TA, which suits its role in storing elastic energy. Both findings suggest that tendon material properties may be muscle-dependent.

This dissertation provides the first view of quantified contributions from different sources to SRS of individual muscles. It was identified that, among these sources, muscle fascicle length, tendon geometry, and tendon material properties are the most essential for determining the whole muscle SRS.

Indexing (document details)
Advisor: Sandercock, Thomas
Commitee: Dhaher, Yasin, Heckman, Charles, Moran, Brian, Perreault, Eric, Sandercock, Thomas
School: Northwestern University
Department: Biomedical Engineering
School Location: United States -- Illinois
Source: DAI-B 68/11, Dissertation Abstracts International
Subjects: Biomedical research
Keywords: Connective tissues, Muscle modeling, Muscle stiffness, Short-range stiffness, Skeletal muscles, Tendon mechanical property
Publication Number: 3284317
ISBN: 978-0-549-29698-0
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