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SUMMARYThis report describes how the resistance to fatigue of a muscle fibre relates to the fibre's most important ATP-producing and ATP-consuming reactions. Twelve intact single muscle fibres were dissected from lumbrical muscles of Xenopus laeris. Their resistance to fatigue induced by repeated tetanic stimulation was determined, as well as their succinate dehydrogenase activity and calcium-stimulated myofibrillar ATPase activity. The enzyme activities were determined by means of quantitative histochemistry. It was found that resistance to fatigue correlates with succinate dehydrogenase activity (r = 0 83) and with myofibrillar ATPase activity (r 0-074). The highest correlation was found between resistance to fatigue and the ratio of succinate dehydrogenase to myofibrillar ATPase activity (r = 0 93). It is concluded that muscular fatigue is closely related to cellular energetics.

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