Factors Contributing to Enhanced Fatigue-Resistance in Low-Frequency Stimulated Muscle
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The ability for sustained contractile activity of skeletal muscle is generally assumed to correlate with a high capacity of aerobic-oxidative energy metabolism. This notion was derived from the observation that muscle fibres differing in their mitochondrial enzyme activities display distinct fatigue properties (4,7,18,22). Motor units composed of fasttwitch glycolytic (FG) fibres are fast-fatiguable, whereas motor units composed of socalled fast-twitch oxidative (FOG) or slow-twitch oxidative (SO) fibres are less fatigable or resistant to fatigue, respectively. Additional evidence in support of this notion has emerged from studies on fast-twitch muscles exposed to chronic electrical stimulation (for review see (25)). A major effect of maximally forced contractile activity by chronic lowfrequency stimulation (CLFS) is that stimulated muscles display pronounced increases in enzyme activities of terminal substrate oxidation (Fig. 1) and become non-fatigable (24,25).
KeywordsMotor Unit Tibialis Anterior Extensor Digitorum Longus Tibialis Anterior Muscle Mitochondrial Enzyme Activity
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