If the output intensity were high enough, any electrical stimulator could cause a muscle contraction, pain, or depolarization of muscle fibers. However, there's a more specific method of targeting specific tissues: altering the pulse duration. This graph shows the relationship between pulse duration, output voltage, and the subsequent depolarization of tissues. Note that at the bottom left of the chart the pulse duration is relatively short, only 5 microseconds (µsec). At this point, there's a clear spread between the depolarization thresholds for each of the three types of nerves. But as the pulse duration increases, the intensity required for depolarization decreases and the separation between thresholds is reduced. So, for example, if you're using a generator that's producing electrical pulses of 360 µsec, it's difficult to stimulate motor nerves without also producing pain.