When active skeletal muscle is stretched, it generally responds with a contraction which resists the stretch. This response is termed the muscle stretch reflex. The size (gain) and timing (phase) of the response has been found to depend on many factors including the characteristics of the applied stretch, the muscle contraction level and the subject's intention. Investigations of this stretch reflex have often involved stretches to muscle which contained frequencies either beyond the range of voluntary movement or else which could be consciously tracked. This study sought to characterise the frequency response of the stretch reflex, in terms of its gain and phase, under a variety of conditions while using stretches to the muscle which were relevant to voluntary movement, yet which were too irregular to be tracked. The types of stretch which satisfied these criteria had first to be determined by an investigation of tracking performance under different conditions of peripheral feedback. Having established the types of stretch which could be used to guarantee reflex rather than voluntary responses, the stretch reflex was investigated using stretches of different amplitude and bandwidth and spanning the full range of contraction level. Research was also undertaken to determine whether the gain and phase of the reflex response could be decoupled from the background contraction level of the muscle and to examine any associated effects on the mechanical properties of the limb. Explanatory models for some of these reflex responses were developed. An interaction between normal physiological tremor and the stretch reflex response was also investigated.

Thesis (Ph. D.)--University of New South Wales, 2000. / Also available online.

Thesis (Ph.D.)--University of Toledo, 2004. / Typescript. "A dissertation [submitted] as partial fulfillment of the requirements of the Doctor of Philosophy degree in Exercise Science." Bibliography: leaves 72-77.

Theses (M.S.)--Marshall University, 2006. / Title from document title page. Includes abstract. Document formatted into pages: contains iv, 43 p. Bibliography: p. 28-30.

N/A / Thesis / Master of Science (MSc)

<p> The performance enhancement of stretch shortening cycle (SSe) contractions has been well documented in the literature. However, the majority of these studies have been performed either on gross human systems for multijointed movements, or in isolated animal muscle studies using in-vitro preparations. This study was designed to apply the principles used for these invitro animal studies to the human system, under conditions that would allow results to be directly associated with a specific muscle or muscle group. Previous investigations by Lynch (1992) and Benoit and Dowling (1995) have supported the use of muscle models to predict elbow flexor torque and sse performance enhancement. The purpose of this study was to use an EMG based muscle model to investigate the possible relationship between sse tasks at different frequencies of elbow flexion-extension and performance enhancement of the elbow flexor muscles. </p> <p> A Hill based muscle model was used to predict elbow flexor torque of seven healthy male subjects (23-40 years of age) under voluntary and stimulated contraction conditions. EMG of the elbow flexors and extensors was recorded from the biceps brachii and triceps respectively. Elbow flexor stimulation was done transcutaneously with a voltage equivalent to a 60% MVe torque; stimulation lasted four seconds at a frequency of 50 Hz. A simulated constant muscle activation torque was also derived from the muscle model for all trials. Externally measured torque was measured using a strain gauge located on a shaft situated along the axis of rotation of the elbow joint. A torque motor was used to drive the forearm (fastened to a manipulandum) at four frequencies of elbow flexion-extension (.58, 1.5, 2.4, and 3.3 Hz) over a range of 162 to 105 degrees of elbow extension. Non-SSe trials were performed at these same velocities and over the same range of motion. Torque was then integrated as a function of joint angle displacement to yield the work produced about the elbow. Passive work was subtracted from all trials. </p> <p> The results indicate that a significant increase in muscle work followed sse tasks as opposed to non-SSe tasks and this increased work was relatively highest at 2.4 Hz. Work about the elbow decreased with increasing frequency of movement for both sse and non-sse conditions. The simulated constant activation muscle model predicted work well for all trials and conditions, indicating muscle model accuracy. The EMG driven model predicted well for all non-SSe trials but significantly underestimated the work for sse tasks, suggesting a decrease in myoelectric activity. This decrease was evidenced by a decrease in average M-wave amplitude with increasing SSe velocity. This study indicates that the contractile component is directly involved in optimizing muscle work during sse tasks and that the performance enhancement of sse tasks may take place at the myofilament and cross-bridge level. </p> / Thesis / Master of Science (MSc)

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No description available.

The study of mechanobiology and the cellular response to the mechanical environment plays a vital role in the understanding of the atherogenesis and the treatment of the disease state through interventions such as stent placement. Cell migration in response to complex stresses also plays a critical role in wound healing. Modeling the mechanical environment as a circular membrane with a center defect can be an accurate representation of in vivo stress gradients. In this study, we created a novel cell stretching device that exposed cells to both static and 1 Hz dynamic stretch. Using NIH 3T3 fibroblasts stained with DiI membrane stain, we were able to expose cells to the two stretch regimes for 48 hours and observe the cellular response via live cell imaging. Cells were observed at 0, 12, 24, and 48 hour time points, and analysis of the change in their radial position was used to determine if cell migration occurred. Cell displacement was calculated using both the kinematic equation and the NeoHookean constitutive model. Uncertainty of the cell displacement calculation was used in determining whether or not there was cell migration. In this study, we were able to prescribe successfully the stretch regimes and observe the cellular response to stretch. Within the bounds of our uncertainty based on the error in the hole radius estimation and our measurement of cell and membrane displacement, however, we cannot say conclusively that cell migration occurred. This study established the methods and protocols necessary for further investigation into mechanobiology, in particular, the cell response to stress environments that more closely resemble the in vivo conditions.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 119-126). Available also in a digital version from Dissertation Abstracts.