Force depression following skeletal muscle shortening is long lasting.

In a recent manuscript, Edman (1996) reported that force depression following shortening was a transient phenomenon. A transient response would not fit into the mechanism of force depression suggested by Herzog and Leonard (1997) who argued that force depression following shortening was associated with a stress-related inhibition of cross-bridge attachments in the actomyosin overlap zone formed during the shortening phase. The purpose of this study was to test whether force depressions were long lasting or transient, and in the process, to quantify the relationship between force depression and the amount of shortening and the shortening force. It was found that force depression in cat soleus (35-37 degrees C) was long lasting and was linearly related to the amount of shortening and the shortening force. This latter result suggested that force depression might possibly be related to a single scalar variable; the mechanical work performed by the muscle during the shortening phase. Although the present study was not designed to test this hypothesis, pilot results support the idea that force depression following shortening contractions might be explained exclusively by the muscular work during the shortening phase.