 cause, your nerves responded with the only survival tool they had: they contracted, they decreased their length and volume to protect themselves, and the spaces in between the nerves(synapse) were extended. A regular sized nerve signal could no longer jump this gap. Specialized stimulator then sends out a "test" signal that represents the most common waveform for healthy peripheral nerves. These impulses are sent out 7.83 times per 2nd since that is how long it takes for the nerve cell to re-polarize (or reset) itself in between its transmission of nerve signals. The signals, (as they cross the synaptic junctions in the nerve roots of the lower back to get from one leg to the other), develop a small electromagnetic field that is sensed by the nerves in your central anxious system (spine) and a signal is uploaded to the brain to let it know what is occurring in the back location.