Dependency of oxygen consumption of skeletal muscle on number of stimuli during work in the dog

¹ Departments of Environmental Medicine and Medicine, The Johns Hopkins University, Baltimore, Maryland

The amount of extra oxygen consumed by skeletal muscle following work (isotonic contractions) or isometric contractions was measured in the normally circulated gastrocnemius-plantaris muscle group of the dog. Work was varied by: a) having the muscle perform the same work a repeated number of times; b) varying the load against which the muscle-contracted, c) varying the amount of shortening of the muscle by limiting the duration of stimulation. The effect of frequency of stimulation was assessed by using two frequencies of stimulation in conditions a) and c). Finally, the extra oxygen consumed following isotonic work was compared with the extra oxygen consumed following isometric tension development. It was found that extra oxygen consumption of skeletal muscle following activity was not a direct consequence of the work done nor was it related linearly to the amount of shortening. The extra oxygen consumption appeared to be a response to the number of nervous stimuli delivered to the muscle. At a sufficiently low frequency each stimulus evoked the consumption of a constant quantum of oxygen. At higher frequencies, after a relatively small number of stimuli, oxygen consumption per stimulus decreased with successive stimuli.

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