Metabolic determinants of activity induced muscular fatigue

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Bibliographic Details
Title translated into German:Determinierende Stoffwechselfaktoren der belastungsbedingten Muskelermuedung
Author:Green, H.J.
Editor:Hargreaves, Mark
Published in:Exercise metabolism
Published:Champaign: Human Kinetics (Verlag), 1995, 1995. S. 211-256, Lit., Lit.
Format: Publications (Database SPOLIT)
Publication Type: Compilation article
Media type: Print resource
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Identification number:PU199810305191

Author's abstract

Identification of the mechanisms underlying neuromuscular fatigue during repetitive, voluntary activity remains the ultimate quest for investigators engaged in research in this area. Although impressive advances have been made and continue to be made, definitive conclusions will continue to prove elusive. There are many reasons for this. In the first case, tasks are generally very complex. They may vary in the intensity, the velocity, and the muscle length at which they are performed. Many tasks also involve recruitment of more than one muscle with highly individualized recruitment and decruitment profiles. The muscles involved in the task may be composed of different fiber types, with different synergistic muscles depending on one fiber type more than another. All of these considerations influence both the onset and the progress of fatigue. Many sites also exist as potential failure points within the contracting muscle cell. Which site becomes limiting and under what conditions remain uncertain. Tasks differ in the challenge placed on the different excitation and contraction processes, and it is possible that this may be an important consideration in the loss of functional integrity experienced by a given process. Impressive progress is being made in understanding activity induced disturbances in selected excitation-contraction processes. In general, the cause of such disturbances has been dichotomized into metabolic and nonmetabolic factors. Metabolic factors address the role of energy potential and the deleterious effects induced by alterations in energy state and by-product accumulation. Nonmetabolic fatigue, or fatigue that occurs in the absence of a significant metabolic disturbance, is also well documented. This type of fatigue is most readily apparent after eccentric exercise where the energy demands are low but the force production is high. Although this type of exercise is accompanied by disruptions in the internal organization of the fiber, it is not clear whether force impairment is due to a specific site or involves a combination of several sites. Nonmetabolic fatigue can also be demonstrated in a variety of tasks and is characterized by a persistent weakness after metabolic recovery has occurred. An intriguing yet unproved hypothesis is that changes in the intracellular environment, mediated by metabolic factors, if allowed to persist for a critical period, induce structural or compositional changes in membranes and proteins at selected intracellular sites. In the voluntary exercising human, identification of a failing site within the muscle may also be complicated by central considerations. lt is generally recognized that some degree of neural compensation is possible to offset failure in the muscle cell. This compensation would appear to involve changing the activation pattern to specific motor units. The degree to which this is possible would depend on the characteristics of the activity. More intense activities reduce the possible strategies that can be invoked because firing frequency and motor unit recruitment are near maximal at the onset of the task. Indeed, with this degree of strain imposed on the excitation and contraction process, changes in the intracellular environment may only have to change minimally to effect deterioration in performance. Verf.-Referat