Fig. 1. Pain tolerance thresholds to 2,000-, 250-, or 5-Hz stimulation on the forearm of volunteers with dark hair (  dark, solid lines ) or red hair (  pale, dashed lines ). Three areas of the arm were tested: an untreated control area, an area treated with 4% liposomal lidocaine, and an area injected with 1 ml lidocaine, 1%. Data were plotted as Kaplan-Meier survival curves, and the curves were compared with log rank tests. The  y-axis represents the fraction of the study population still able to reach a particular threshold. The curves for the two groups were significantly different for all three frequencies on the area treated subcutaneously with lidocaine.