The CO-dispersion index for the measurement of fiber type distribution patterns

There is a need for a practical and statistically manageable quantitative index of fiber type co‐dispersion in skeletal muscle to allow investigation of the distribution of motor units in normal muscle and their rearrangement in pathological states. A new measure for this purpose, the Co‐Dispersion Index (CDI), is introduced. This measure is based on contingency table analysis of nearest‐neighbor relationships between muscle fibers. The CDI has a continuous range of values from −1 to +1, in which larger negative values indicate a greater tendency toward regular intermixing of fibers of different types, and larger positive values a greater segregation of fiber types. CDI evaluation overcomes the limitations of previously published quantitative methods for codispersion measurement and is well correlated with subjective human estimates of fiber type grouping.