Modern TENS units work with a dual channel, so the first thing to avoid are machines which indicate applying electrodes marked with negative positive poles. This is incorrect and confusing.
Nowadays, electrodes emit an asymmetric biphasic square pulse which avoids the painful effects of previous machine which caused chemical burns due to the polar effects of the current.
From here on we indicate whether the electrodes are placed close to a muscle group or further away, using the terms ‘proximal’ and ‘distal’, respectively.
Assuming that the above information has been understood, we explain here the colour code which will help us apply the electrodes quickly, remembering always that colour does not necessarily indicate polarity.