A shoe having a rubberized sole, a heel section having a heel support, an at least partially covered toe section, and a generally open midsection extending from approximately the wearer’s toeinstep joint to the front of the wearer’s ankle. The substance unit includes a substance layer. To optimize latency during sampling, the number of page hits and number of page misses are multiplied by weighted values WPH and WPM, respectively, such that the weighted function \u2212 is maximized. A microprocessor controls the switching waveform controller and the switching high frequency generator.