MUSCLE VOLUME CHANGES: RELATION TO THE ACTIVE STATE.

The volume of a frog sartorius muscle increases during a single twitch and subsequently decreases. The magnitude of volume change is 10(-5) cm(3) per gram of muscle. The time courses of change in volume and of onset of tension vary with temperature in a similar way, which implies a relation between the volume changes and the contraction mechanism. The character of the change depends upon the initial length of the muscle: the greatest decrease accompanies an isometric twitch at reference length. Treatment of the muscle with an iodide Ringer solution prolongs the active state and the volume change. These results suggest a correlation between the volume changes and the active state.