SUBMAXIMAL STIMULI ACTIVATE DIFFERENT NERVE-FIBER POPULATIONS AT DIFFERENT SITES

Theoretically, the largest and fastest nerve fibers are preferentially stimulated with submaximal stimuli. However, it is also well known th at intraneural fascicular topography changes substantially along a pro ximal to distal axis. Because of this change in fascicular topography, we hypothesized that percutaneous submaximal stimuli applied to a ner ve at different locations would stimulate different subpopulations of large fibers. We performed a series of collision studies by stimulatin g the ulnar nerve submaximally at proximal and distal sites at varying levels of stimulation intensity from motor threshold to supramaximal stimulation. The results suggest that variation in intraneural topogra phy at different sites allows different large diameter nerve fiber sub populations to be activated at submaximal stimuli, and emphasizes the importance of supramaximal stimulation to determine a valid conduction velocity. (C) 1994 John Wiley and Sons, Inc.