Studies on the morphometry and mechanical properties of mammalian muscle

Three experiments were performed on the mechanical properties of two cat hindlimb muscles. To begin, the effects of fascicle length and velocity on force output of cat soleus muscle are described. The muscle force was recorded during whole-muscle isometric and isokinetic contractions, while the length of a muscle force was recorded using ultrasound techniques. The results demonstrate that there were systematic differences between the kinematics imposed on the whole-muscle and the observed kinematics of the fascicles. Moreover, the results demonstrated a systematic, but previously unknown interdependence between fascicle length and velocity on muscle force production.

The second study analyzed the mechanical properties of the aponeurosis and tendon of the cat soleus muscle during whole-muscle isometric contractions. The length of the aponeurosis was found to be dependent on muscle force, but not dependent on the length of the fascicles attached to it as suggested by previous studies. Rather, the mechanical properties of the aponeurosis appeared to be similar to tendon. The stiffness of both of these tissues were found to be matched closely to the force generating capacity of the parent muscle.

The third study in the thesis looked at the mechanical properties of the feline anterior sartorius, a long strap-like muscle composed of short muscle fibres. Nerve branches that enter this muscle contain the axons of motor units whose constituent muscle fibers are distributed asymmetrically within the muscle. Muscle force and intramuscular lengths were recorded during stimulation of the individual nerve branches or the parent nerve. Stimulation of the individual nerve branches caused the muscle to shorten at the end closest to the nerve branch and lengthen at the opposite end. The force-length relationships obtained by stimulating the individual nerve branches were not congruent to the relationship obtained by stimulating the parent nerve. The results suggest that a complex relationship between passive and active elements contributes to total muscle force.

The final study in the thesis is concerned with obtaining the morphometric data needed to develop quantitative muscle models for human subjects. Striation patterns spanning individual muscles in longitudinally oriented MR images appear to represent accurately the orientation of the muscle fascicles. Mathematical techniques were developed and used to compute the three-dimensional orientation and projected length of the fascicles from MR images of vastus medialis and semimembranosus muscles from a human cadaver. The morphometric properties estimated from the MR images matched closely the values obtained directly by dissection. The use of MR images to estimate the morphometry of individual muscles reduces the number of unknown or indirectly measured parameters of muscle models and thus improves their predictive capabilities. (Abstract shortened by UMI.)