Is the F wave elicited in a select group of motoneurons?

The F wave represents only a small percentage of the motoneuron pool invaded antidromically by any single impulse. We studied 22 median nerves from 11 healthy subjects to determine whether the recurrent discharges are preferentially generated in a select group of motoneurons with certain physiologic characteristics. Partial excitation of the nerve elicited the F wave with no consistent bias toward either the lower or higher threshold motor fibers. When the fast conducting axons were progressively blocked using a collision technique, the F wave continued to appear in the remaining slow conducting axons which escaped the collision. We conclude that the recurrent discharges occur in approximately 1% of antidromically activated motoneurons irrespective of their peripheral excitability or conduction characteristics.