Pseudofacilitation: A temperature-sensitive phenomenon

With sustained isometric exercise, compound muscle action potential (CMAP) amplitude of normal subjects may increase, a phenomenon known as pseudofacilitation. To explore the mechanism of pseudofacilitation, the effect of exercise combined with focal heating and cooling of abductor pollicis brevis was examined in 10 normal subjects. After 10 s of isometric exercise, CMAP amplitude increased by 3.6% (median value) at 32 degrees C and 6.4% at 40 degrees C, and decreased by 9.1% at 20 degrees C. Duration decreased by 12.6% at 32 degrees C and 11.7% at 42 degrees C, but increased by 12.4% at 20 degrees C. Area decreased by 9.8% at 32 degrees C and 8. 6% at 42 degrees C, and increased by 1.1% at 20 degrees C. Changes with cooling were significant (P < 0.01) as compared to baseline (32 degrees C); changes with heating were not. Thus, cooling reverses the expected increase in CMAP amplitude normally seen with exercise. Although providing only indirect evidence, these findings are consistent with the hypothesis that increased activity of muscle Na(+),K(+)-pump plays a role in producing pseudofacilitation.