Force-velocity relation in paired frog sartorius muscles attached to opposite lever arms.

To study the mechanism of the longitudinal stability at the level of whole muscles, paired frog sartorius muscles were attached to the opposite lever arms at unequal distances from the pivot. The lever was initially fixed in position, and when the full isometric forces were developed in both muscles, it was released to move, the result being that the advantaged muscle shortened by stretching the disadvantaged one with a nearly constant velocity depending on the ratio between their points of attachment from the pivot. The force-velocity relation of the advantaged muscle was virtually identical with the ordinary force-velocity relation obtained from the isotonic release experiments, while the force-velocity relation of the disadvantaged muscle was found to be entirely different from the ordinary one because of a marked increase in the load-bearing ability. These results are discussed in connection with the enhancement of mechanical performance in lengthening muscle.