Thesis (doctoral)--Universitatis Tartuensis, 2006. / Includes bibliographical references.

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Empirical and simulation studies are described which assess the form of central control signals for human limb movement. Recent claims about the complexity of control signals are addressed using a mathematical model of two-joint planar arm movement. The model is based on the lambda version of the equilibrium point hypothesis and includes neural control signals, reflexes, reflex delays, muscle mechanical properties, realistic musculo-skeletal geometry, limb dynamics and external loads. It is shown that ostensibly "complex" features of limb motion such as the "2/3 power law" and non-monotonic patterns of limb impedance are predicted using simple constant-rate equilibrium shifts which do not explicitly encode these movement properties. In addition it is shown that simulated limb impedance using the A model both during movement and in statics matches empirically estimated values of impedance reported in the literature. / Empirical studies assessed the control of muscle coactivation by measuring tonic levels of electromyographic activity in shoulder and elbow muscles at the end of reaching movements in a horizontal plane. Shoulder muscle coactivation was related to the amplitude and velocity of shoulder motion, and unrelated to elbow motion whereas elbow and double-joint muscle activity was related to elbow motion, and unrelated to shoulder motion. It is suggested that muscle coactivation at the shoulder and elbow may be controlled independently. / Other experiments addressed the extent to which control signals are adjusted to account for interaction torques---torques arising at one joint due to the motion of limb segments about adjacent joints. Electromyographic activity of limb muscles was measured during single- and multi-joint movements in which the magnitude or direction of interaction torque was systematically varied. During single-joint movements, phasic activity which preceded motion and varied in magnitude with interaction torque was observed in muscles acting at the stationary joint. During multi-joint movement EMG activity in muscles at one joint was modulated to offset interaction torque arising from limb motion about an adjacent joint. It is suggested that control signals to muscles are adjusted to offset interaction torques arising from limb dynamics. Schemes for incorporating information about dynamics into the position control framework proposed in the equilibrium point hypothesis are discussed.

Thesis (M.S.)--Ohio University, June, 2008. / Title from PDF t.p. Includes bibliographical references.

Skeletal muscles of the limb are derived from somites and their precursors migrate to the limb prior to muscle formation. Upon migration, a limited number of stem cells multiply and differentiate to give rise to fusion-competent muscle cells, which fuse to form the multinucleated myotubes. During the course of myogenesis there is thus a period of few days when cells at different developmental stages such as migrating, proliferating, differentiating and fully differentiated co-reside within the developing limb bud. Current understanding on how these cells interact and behave during early and later myogenesis in vivo is lacking. The aim of this project was to identify and further classify the mononucleated myogenic cells present within the developing limb muscle and examine their behaviours at different stages of myogenesis. The lack of an appropriate method to extract and visualise cellular constituents of developing muscles has been a major limitation hindering such investigations in vivo. In this project, we first developed a unique cell isolation method to extract mononucleated cells from developing muscles, allowing examination of mononucleated cells in vivo using immunocytochemistry. As Pax3, Pax7 and Myogenic Regulatory Factors (MRFs) are the key players for the muscle formation, they were used to mark the different myogenic sub-populations. The results from chicken and rats clearly demonstrate that three myogenic cell pools, namely Pax3, Pax7 and MRFs positive cells, and 4 sub-populations formed by their overlap, co-exist in specific proportions within the developing limb muscle, and that their proportions undergo dynamic changes during the course of myogenesis. The most striking observation was that the sizes of Pax3 and MRF compartments remain constant while that of Pax7 compartment increases dramatically during myogenesis. Thus each myogenic cell compartment in the developing muscle has different cell kinetics during primary and secondary myogenesis. The dynamic changes in the proportions of these myogenic sub-populations may constitute a dynamically maintained cellular niche, within which the muscle stem cells reside. Our study suggests that the concept of community effect - the interaction between a group of cells and their surrounding cells, originally from invertebrate muscle system, may be conserved in mammalian systems. Furthermore, this study for the first time, reports that the earliest fully differentiate muscle cells in the rat hindlimb are highly elongated mononucleated cells which express Pax3, MyoD, myogenin and myosin but not Myf-5 protein. In summary, this study provides quantitative data to demonstrate dynamic changes in various mononucleated myogenic cell populations during skeletal muscle formation and reveals that Pax7(+ve) population becomes significantly upregulated during secondary myogenesis.

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 127-142).

Thesis (Ph.D.)--Ohio University, August, 2004. / Includes bibliographical references.

It has been shown that maximal, bilateral efforts result in both a force and EMG deficit when compared to maximal, unilateral activation of the same musculature. It is unclear whether this deficit is the result of interactions of central or peripheral origin. The first aim study investigated the bilateral performance index (BPI (%) = [100 x bilateral force/(right unilateral + left unilateral forces)] - 100) for maximal, isometric, extensor torques about the knee joint in three groups of subjects: untrained (never lifted weights), cyclists (leg musculature trained reciprocally), and weightlifters (legs trained bilaterally). The BPI for the weightlifters (+7.0 ± 5.0%) was significantly (p < 0.05) greater than the BPI of the cyclists (-4.0 ± 6.3%) or the untrained subjects (-9.7 ± 5.2%). These results indicate that the inhibitory mechanisms previously proposed to act during bilateral efforts are inadequate, and that excitatory factors must be present to achieve a BPI > 0. The second aim study showed that the BPI can be altered as a result of three weeks of bilateral isometric strength training. The BPI's for the control and unilateral training groups were not significantly different pre- to posttraining. However, the BPI of the bilateral training group increased significantly (p < 0.05) from -3.7 ± 6.9% prior to training, to +4.2 ± 4.4% after training. These findings indicate that bilateral strength training can alter the relationship between unilateral and bilateral force output. The third aim study demonstrated that subjects with a positive BPI (+6.8 ± 4.3%) responded differently to an afferent perturbation (electrical stimulation) than subjects with a negative BPI (-10.0 ± 5.2%). The negative BPI group showed a 5.7 ± 3.4% facilitation in force during contralateral electrical stimulation. This was significantly (p < 0.05) less than the 16.5 ± 7.5% facilitation shown by the positive BPI group. These results indicate that afferent feedback can alter the force output in the contralateral limb, and may thereby play a role in unilateral-bilateral force differences.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Biomedical Engineering." Includes bibliographical references (p. 95-99).

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xv, 239 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.