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Muscle Fatigue Induced by Sustained Isometric Contraction

An important potential thermodynamic criterion for the condition of muscle fatigue induced by a single sustained isometric contraction is discussed, and a method is suggested for its use in determining the duration for which any given static contraction will be sustained before the condition of fatigue is reached. In a healthy rested muscle, under given environmental conditions, the production of a critical amount of heat caused by local regional metabolism is postulated as a necessary response to sustained static effort beyond 15% MVC before fatigue can occur. Muscle response is expressed here as a percent of maximum voluntary contraction (% MVC), a relative unit for each group of muscles which is a suitable measure of the actual level of physiological stimulus for any muscle. A relation between static muscle tension, the duration for which such a tension is sustained, and the critical amount of heat produced until the onset of fatigue is derived. It is assumed that the amount of heat liberated in the muscle during regional metabolism can be measured.