Key point
With classic, unidirectional stimulation currents the negative electrode (cathode) has a stronger excitatory effect, which is why it is moved to the treatment points. Modern, biphasic TENS and EMS devices, however, reverse current direction continuously, so polarity loses its practical significance here – electrode placement, not the marking, matters.
How do the two poles affect living tissue?
To judge the question of polarity, it is useful first to look at what the positive and negative electrodes do individually – and what happens when the device switches between them in rapid succession.
Under the negative electrode the external surface of the cell membrane becomes more negative due to the current. This facilitates activation of nerve and muscle fibers.1,2
This property is exploited in classic unidirectional stimulation: the cathode is the so‑called active electrode, which the therapist places over motor (movement) points where muscle twitching or nerve excitation can be evoked with the lowest current.
Under the positive pole the effect is reversed: the cell membrane hyperpolarizes, making it less likely to fire. Therefore the anode by itself is generally not an effective stimulating electrode.1
In classic procedures the anode usually serves an indifferent or return role: it closes the circuit and provides a stable base for the treatment. That is why it is often fixed in place.
Most modern TENS, EMS and NMES devices operate with so‑called biphasic pulses. This means the current direction reverses within each pulse: in the first microseconds one electrode acts as the cathode, immediately followed by the other.3
Since both poles alternately serve as cathode and anode, there is no sustained "positive" or "negative" electrode. That is why polarity has no practical significance on modern devices – the device essentially works back and forth between the two electrodes.
Classic vs modern methods – what’s the practical difference?
Throughout the history of electrotherapy several generations of devices have appeared. From the polarity point of view it is useful to distinguish two main groups: classic procedures using a unidirectional current, and modern devices that deliver biphasic pulses.
| Aspect | Classic, unidirectional current | Modern, biphasic pulse |
|---|---|---|
| Typical procedures | Galvanic current, stimulation currents (Träbert, diadynamic currents), iontophoresis | TENS, EMS, NMES, interferential current |
| Current direction | Always flows in the same direction | Continuously changes direction |
| Significance of polarity | Significant – cathode and anode have different effects | Minimal or none – the two electrodes are practically equal |
| Active electrode | The negative (cathode), which the therapist moves | No "active" electrode – placement matters |
| Typical placement | Anode: fixed, indifferent Cathode: on motor points, moved |
Both electrodes around the treated area |
| Typical use | Diagnostics, treatment of denervated muscle, iontophoresis | Home pain relief, muscle strengthening, muscle recovery |
The table shows that if someone remembers a fixed positive electrode from older physiotherapy sessions, they likely recall a classic unidirectional stimulation treatment. Home TENS and EMS devices typically operate with a different waveform.
Where to place the electrodes? – Practical considerations
Whether you use a classic or a modern device, electrode placement is more important than the waveform itself. Below we review the most common situations.
Most TENS devices operate with biphasic pulses, so polarity is not relevant here. Place the two electrodes around the painful area or along the course of the affected nerve so that the painful spot lies between the electrodes. General rule: electrodes should not touch each other, and there should be at least about 5 centimeters between them.
For a more detailed guide, see our article on home use of TENS devices for drug‑free pain relief.
EMS and NMES devices aim to directly stimulate muscle. Most modern devices also use biphasic pulses, so the key is finding the motor point rather than worrying about polarity. The motor point is the area where the nerve enters the muscle – here relatively low current can elicit a contraction.
Exact electrode positions differ by muscle and should be learned from the device manual or a professional.
With unidirectional pulsed stimulation (for example, when treating denervated muscle) polarity matters: the negative electrode is the active one and is placed by the therapist on the motor point, while the positive electrode is fixed in an indifferent position.
Modern devices designed for long‑term home selective stimulation (PeroBravo, Genesy 600, Genesy 1500, Genesy 3000) reverse current direction after each pulse, so polarity does not need to be considered for these devices!
Traditional iontophoresis for drug delivery uses direct current, and polarity can be important. The charge of the drug determines under which electrode it is placed: positively charged ions enter under the anode, negatively charged ions under the cathode. Iontophoresis should always be performed according to the drug and device instructions.
Electrotherapy devices for home use
The device categories below are available in the Medimarket range and all use modern technology with biphasic or adjustable pulse types – so users practically do not need to worry about polarity.
TENS devices
Devices that deliver primarily biphasic pulses for pain relief. Suitable for home use and typically come with multiple built‑in programs.
EMS and NMES devices
Muscle stimulators developed for muscle strengthening, recovery and maintenance of muscle tone. Suitable for athletes, rehabilitation and home training.
Before you start treatment
Electrotherapy is generally well tolerated, but there are some conditions when it is not recommended or should only be used after medical consultation. The list below summarizes the most common contraindications.
When should you be cautious?
- Implanted pacemaker or other active implant – the current can interfere with device function. In such cases always consult the treating physician.
- Pregnancy – especially treatment of the abdomen and lower back should be avoided unless recommended by a physician.
- Active malignant disease – electrotherapy is not recommended in the immediate vicinity of a treated tumor.
- Anterior neck area, eye, temple – sensitive nerves and vessels run here and electrodes must not be placed over these sites.
- Damaged, inflamed or insensitive skin – with reduced sensation excessive current may not be felt and can cause burns.
- Fever or infectious condition – avoid electrotherapy during acute illness.
- Epilepsy, cardiac arrhythmia – in these cases treatment should only be performed with the permission and supervision of the treating physician.
Important information
Home electrotherapy devices are intended to complement medical treatment, not replace it. If you have persistent complaints, you should first consult your treating physician about the appropriate therapeutic approach.
Scientific background
The differential effects of polarity are not only clinical observations but have been studied and well documented for decades. A few interesting data points from the literature:
Cathode vs anode stimulation threshold (Tsui et al., 2010)
Peripheral nerve measurements indicate that the cathode can elicit a nerve response at roughly 50% lower current than the anode. The cathode’s minimal threshold was 0.34 mA versus 0.63 mA for the anode. This quantitatively supports why the negative pole is used as the active electrode in classic procedures.2
Different neural mechanisms of anode and cathode (Manola et al., 2007)
Modeling studies suggest the anode and cathode preferentially excite nerve elements with different orientations: anodal stimulation tends to activate elements perpendicular to the surface, whereas cathodal stimulation more strongly affects fibers parallel to the surface. This helps explain why they do not substitute for each other in classic procedures.1
Biphasic waveform and polarity (Kloth, 2014)
Review studies indicate that symmetric biphasic waveforms have equal charge in both phases, meaning electrodes do not have a pronounced polarity. This is one reason modern TENS and EMS devices do not require users to set polarity separately.3
Practical tips for electrode use
My advice
Most mistakes in electrotherapy arise not from polarity but from electrode condition and placement. A few basic rules:
- Skin under the electrodes should be clean, dry, intact and free of oils.
- Electrodes should not touch and must not slip during treatment.
- Always start at the lowest intensity and gradually increase to a pleasant, definite but not painful sensation.
- Replace electrode gel pads in time – worn or dried pads conduct poorly and may cause skin irritation.
- Treating the face, front of the neck and area around the ears should always be done following a professional’s guidance.
Frequently asked questions
The color coding mainly helps you distinguish the two electrodes and follow the diagrams in the manual. Most home TENS and EMS devices use biphasic pulses, so cable color does not indicate a permanent positive or negative pole in terms of effect.
With modern, biphasic TENS or EMS devices practically nothing – the effect remains the same. With older, unidirectional stimulation devices the sensation and strength of stimulation may change, so it is important to follow the manual and the therapist’s instructions for those devices.
This is usually indicated in the user manual. Most home TENS, EMS and NMES devices use biphasic or asymmetric biphasic pulses. If the description contains "biphasic" then you don’t need to worry about polarity. If your device is old and explicitly offers direct current or a "monophasic" mode, use such modes only on professional advice.
With unidirectional current different chemical processes occur under the anode and cathode, which can cause different skin reactions. With biphasic current this is absent or much less common; in those cases irritation is more likely due to a worn electrode, dry skin, too high intensity, or too long treatment time. If you experience persistent redness or itching, reduce the current, shorten the session, and use a fresh electrode.
The face, anterior neck, temples and area around the ears are sensitive: because of nerves, vessels and the proximity of the thyroid gland these areas require extra caution. Treat these areas with a home device only if a physician or physiotherapist has provided a specific protocol.
Summary – Quick overview
Sources
- Manola L, Holsheimer J, Veltink P, Buitenweg JR (2007). Anodal vs cathodal stimulation of motor cortex: a modeling study. Clinical Neurophysiology. PubMed: 17150409
- Tsui BC, Wagner A, Finucane B (2010). Current-distance relationships for peripheral nerve stimulation localization. Anesthesia & Analgesia. PubMed: 20966439
- Kloth LC (2014). Electrical Stimulation Technologies for Wound Healing. Advances in Wound Care. PMC3929255
- Steigerwald F, Müller L, Johannes S, Matthies C, Volkmann J (2018). Anodic versus cathodic neurostimulation of the subthalamic nucleus: A randomized-controlled study of acute clinical effects. Parkinsonism & Related Disorders. ScienceDirect
