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 co-dispersion measurement and is well correlated with subjective human estimates of fiber type grouping.