Abstract
When the force which is exerted by a muscle is plotted, on the ordinates, against the speed with which it shortens, on the abscissae, the curve relating the two variables is, in general, a straight line sloping towards the x axis. This relationship between force and velocity means that the force exerted by a muscle diminishes as its speed of contraction increases. This result has appeared in the work of Gasser and Hill, 1 Fenn 2 and in our own experiments soon to be published at length elsewhere. The purpose of this paper is to report a fact which emerges from our data which seems to throw light on the cause of the force-velocity relation.
Our experiments were made on the gastrocnemius muscle of the decerebrate cat stimulated through the tibial nerve by a single maximal, break, shock of a Harvard inductorium. The muscular response was, therefore, a twitch. The muscle contracted against an inertia disc (radius 8.65 cm.) the moment of inertia of which was 290,400 gm.-cm. 2 The displacement of the disc was recorded optically. Time was imprinted on the record in intervals of .001″ by means of a slotted disc which was rotated by a synchronous motor in such a way as to interrupt a thin beam of light from a 500 watt lamp. The displacement of the inertia disc was measured from the photographic record with a cathetometer for each .001″ and from these measurements, by taking first and second differences, the angular velocity and angular acceleration of the disc were computed. Although this record was measured to each .001″, we have used in this computation, the interval of .01″. The force, calculated from the moment of inertia and the angular acceleration of the disc, is, therefore, known for each time interval (.01″) during the contraction cycle.
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