Skeletal Muscle Response During the Isometric Phase of an Unrestricted Isotonic Contraction (Electromyography, Electromechanical Delay)
Grabiner, Mark Dean
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https://hdl.handle.net/2142/71878
Description
Title
Skeletal Muscle Response During the Isometric Phase of an Unrestricted Isotonic Contraction (Electromyography, Electromechanical Delay)
Author(s)
Grabiner, Mark Dean
Issue Date
1985
Department of Study
Physical Education
Discipline
Physical Education
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Health Sciences, Pharmacology
Education, Physical
Abstract
The purpose of this investigation was to noninvasively determine the contribution of elastic recoil to concentric muscular contraction initiated from a resting state. The noninvasive estimation of the muscular elastic characteristics involved the direct measurement of several neuromuscular and mechanical parameters and the derivation of two additional variables. The derived variables were muscular velocity of contraction and a mechanical index. The latter represented the degree of elastic lengthening during the electromechanical delay (EMD). It was subsequently used to determine elastic recoil contributions to the concentric contraction phase using a statistical model. The model was based upon the anatomical, physiological and mechanical relationships of the involved variables. Fifteen male subjects performed a series of 10 elbow extensions from three initial joint positions and four normalized movement velocities (maximal and three submaximal levels). On-line electromyography from the medial head of the triceps brachii muscle, accelerometry, and electrogoniometry were implemented with a specially-built dynamometer. The dynamometer was a low-friction, low-moment of inertia device which precluded any planar movement other than in the desired transverse plane. Directly measured variables included the integrated EMG during EMD, the duration of EMD, peak acceleration, time to peak acceleration, average jerk, and the duration of the positive acceleration. Initial repeated measures ANOVA procedures indicated statistically significant effects on the variables with respect to initial muscle length and level of effort. Of particular interest was the inconsistent statistical behavior of the EMD which did not allow discrimination between levels of effort at the various muscle lengths as well as demonstrating weak relationships with the other variables. Mechanical index displayed stronger correlations than motor reaction time with the neuromuscular variables and a greater proportion of the mechanical variables. A second statistical procedure, path analysis, was performed to determine the contribution of the mechanical index to the intital positive work phase of the concentric contraction. Results indicated that the mechanical processes occurring during the EMD, expressed as the mechanical index, did not provide statistical evidence of influencing the initial phase of the concentric muscle contraction. It was concluded that concentric contractions initiated without an extended isometric phase or an eccentric lengthening are not influenced by an elastic recoil.
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