High and low frequency electrode placement

Whether the frequency of TENS therapy is high or low has an influence on electrode placement. Furthermore, the lead wires that are connected to the electrodes usually have a black pin and a red pin. Therefore, you may have the 1.5’’ or 2’’ square cloth electrodes, or any other type of electrodes, but when it comes to lead connector pins, the pads may be known simply by the corresponding color, be it black or red. It may also happen to be that the frequency and color have no bearing on placement, as well. 
In phantom pain, high frequency involves placing the electrodes paravertebrally (beside the vertebral column) in the same sector as the pain. Should sensitivity be normal, electrodes may be placed on the opposite side’s foot, for instance. In low frequency, the electrode pads are placed in the opposite side, in the same group of muscles (myotome) as the pain. 
In back pain, it is immaterial where the red and black pins are placed; simply attach the electrode pads over the affected area. Large electrodes, such as the 4’’ x 6’’ butterfly foam electrodes for example, work well with high frequency.
In postherpetic neuralgia (pain from shingles), high frequency entails placing the electrode pads where sensitivity is normal, right over or under the affected area’s dermatome (the area of skin supplied with afferent nerve fibers by a single posterior spinal root), or in the same section on the opposite side. For low frequency, the electrode should be placed so as to produce strong contractions in the innervated (i.e. containing nerves) intercoastal musculature in the 6th-7th vertebrae. Admittedly, that might be a bit difficult to accomplish.

In neck and arm pain (cervical rhizopathy*), high frequency calls for stimulation in the painful site, if sensitivity is normal. Low frequency warrants stimulation over the muscles in the myotome, like the biceps or the carpal radial extensors.
In backache and sciatica (lumbago with sacral rhizopathy), treatment should consist of high frequency in the lumbar area and low frequency on the leg where there is reduced sensitivity. 
In sciatica (lumbosacral rhizopathy), high frequency involves electrode pad placement on the innervated skin over L4 lumbar vertebra if sensitivity is normal, while low frequency is similar, though preferably with a diagonal position which frequently provides good contractions. 
Shoulder pain admits of both high and possible low frequency, placing one electrode pad over the joint space and the other over the deltoid insertion (the deltoid is the thick, triangular muscle that covers the shoulder joint). 

Related Read: Electrode Placement Guide