The relation between force and integrated electrical activity in fatigued muscle

It has been shown by Lippold (1952) and Bigland, Hutter & Lippold (1953) that the force of an isometric contraction of a mammalian muscle is proportional to the voltage-time integral of the electrical activity recorded from it. For practical use to be made of these observations, it is necessary to determine the limits within which this relationship holds. If, for instance, a voluntary contraction is to be maintained at a constant tension, it might be expected that more motor units would be recruited as the tension developed by fatigued units declined. Such an occurrence would alter, with the degree of fatigue, the proportionality between electrical activity and tension. Other factors in fatigue may well influence the relation, such as neuromuscular block (Brown & Burns, 1949) or the effect of activity on the size of action potentials (Brown & von Euler, 1938). The experiments to be reported here were designed to investigate the relation between the electrical activity and the tension of isometrically contracting human muscle under conditions of fatigue.

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