Correlation between histochemistry and muscle activity of jaw muscles in cats

Studies on limb muscles of mammals indicate that the pattern of electromyographic (EMG) activity reflects the histochemical profile of the muscle. This relationship suggests that EMG activity may permit a prediction of certain morphological characteristics of the muscle being studied. In this study numerical descriptors of EMG activity of the masticatory muscles of cats are correlated with the distribution of fiber types, as well as with fiber and fascicle areas, to test the extent to which EMG can be used to predict regional morphology. The results show that the level of EMG activity and its duration have a significant positive correlation with the percentage of slow- and fast-twitch fatigue-resistant fibers and a significant negative correlation with the percentage of fast-twitch fatigable fibers and the ratio of fast-twitch fatigable to fast-twitch fatigue-resistant, plus slow fibers. No correlation was found between activity and fiber cross-sectional area; the descriptors showing significant correlation vary with the hardness of the food. Thus the level of EMG activity and its duration seemingly do provide an indicator of the relative difference in fiber distribution among muscles in a species.