CMAP amplitude cartography of muscles innervated by the median, ulnar, peroneal, and tibial nerves

The spatial and temporal distribution of compound muscle action potential ( CMAP) amplitudes was mapped using 1 x 1-cm grids over thenar, hypothenar, d orsal foot, and foot sole muscles (seven maps each), The high-amplitude zon e (HAZ, area where amplitudes were over 80% of the maximum amplitude) denot ed susceptibility to changes in recording site. Thenar maps had one peak (s patially and temporally) with a HAZ of 3.5 +/- 2.3 cm(2). Hypothenar maps h ad two peaks (spatially and temporally) with a HAZ of 7.7 +/- 3.6 cm(2). Do rsal foot maps had one temporal peak, which could be split up spatially; th e HAZ was smallest, at 1.7 +/- 1.7 cm(2). Foot sole muscles had one peak (s patially and temporally), with the largest HAZ at 18.4 +/- 6.1 cm(2). Wave- form differences were ascribed to differences in muscle anatomy, architectu re, and variability, These explain differences in amplitude reproducibility between nerves and the differing effect that increasing electrode size has on reproducibility, (C) 1999 John Wiley & Sons, Inc.