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Voluntary and Evoked Contractile Properties of Trained, Untrained, and Previously Immobilized Subjects Before and Following Fatigue

出版	National Library of Canada = Bibliothèque nationale du Canada, 1996
URL	http://books.google.com.hk/books?id=W6mWAQAACAAJ&hl=&source=gbs_api

註釋"A series of studies were conducted to investigate differences in voluntary and evoked contractile properties of trained, untrained and previously immobilized ankle fracture subjects before and following fatigue. Measurements included twitch contractile properties, maximal voluntary contractions (MVC), electromyography (EMG) and muscle activation (interpolated twitch (IT) ratio and second order polynomials). Although second order polynomials were found to be a more precise measurement of muscle activation ($ sim$6% error) than the IT ratio (superimposed evoked torque/potentiated resting evoked torque), both techniques provided a general estimate of muscle activation before and following fatigue. Prior to fatigue, trained plantarflexor subjects exerted greater force (17.5%) and had significantly less antagonist activity (41.3%) than untrained subjects. Following fatigue, untrained subjects experienced greater deficits in excitation-contraction coupling and increased antagonist activity (58%) contributing to their tendency for increased fatiguability. The lower force output (45.8%) and muscle activation (20.4%) of previously immobilized non-fixated ankle fractures did not result in greater fatiguability than controls. Disuse adaptations such as potentiation of the muscle action potentials and twitch torque helped to maintain the fatiguing contractions. However the more severely fractured ankles of the internally-fixated subjects experienced increased agonist (13%) and antagonist (8.5%) EMG activity and similar changes in muscle activation and evoked contractile properties while performing fewer contractions. This would suggest that injuries of greater severity may result in an intrinsically more fatiguable muscle. To determine whether the findings could be generalized to other muscles and fatigue protocols, various contraction intensities were used to elicit short and long duration fatiguing contractions in the plantarflexors and quadriceps. Muscle activation, and t"--