# TENS and Interferential Therapy > TENS and interferential therapy in Physiotherapy: conventional and acupuncture-like TENS settings, interferential beat frequency, electrode placement and indications. - Canonical URL: https://prepelephant.com/topics/allied/physiotherapy/tens-and-interferential-therapy - Exam / course: Allied Health · Subject: Physiotherapy - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "TENS and Interferential Therapy", PrepElephant, https://prepelephant.com/topics/allied/physiotherapy/tens-and-interferential-therapy ## Direct answer Rub a freshly knocked elbow and the ache dulls — Melzack and Wall's gate control theory turned that everyday reflex into the rationale for TENS. Transcutaneous electrical nerve stimulation delivers low-intensity pulses through skin electrodes for analgesia: conventional TENS uses high frequency (commonly 50–100 hertz) with short pulse durations for fast but short-lived relief, while acupuncture-like TENS uses low frequency (2–4 hertz) at motor-level intensity for slower-onset, longer relief through endogenous opioids. Interferential therapy crosses two medium-frequency currents — classically around 4000 hertz — inside the tissues so that their difference, the beat frequency, delivers the low-frequency treatment effect at depth with far greater comfort. ## What you must remember - Conventional TENS: high frequency (roughly 50–100 hertz), short pulse duration (about 50–80 microseconds), intensity at strong-but-comfortable sensory level; onset within minutes, relief outlasting stimulation by minutes to hours; gate control mechanism. - Acupuncture-like TENS: low frequency (2–4 hertz), longer pulses (150–250 microseconds), intensity high enough to produce visible muscle contractions; slower onset, longer after-effect through beta-endorphin release — reversible by naloxone, the classic examination evidence. - Brief intense TENS — high frequency, high intensity, short duration — is reserved for procedures such as needle insertion. - Electrode options: over the painful area, along the peripheral nerve course, or paravertebrally at the relevant segment; spacing at least one electrode-width apart prevents current short-circuiting between pads. - Interferential physics: two channel outputs, four electrodes in quadripolar cross-formation; currents of, say, 4000 and 4125 hertz interfere inside the tissue to yield a 125-hertz beat equal to their difference. - Beat frequency is chosen by goal — commonly around 80–150 hertz for conventional analgesia, 20–50 hertz for muscle stimulation, 1–4 hertz for acupuncture-like effects — and many units sweep the beat to prevent habituation. - Interferential's advantages: medium-frequency carriers meet low skin impedance, so the current penetrates deeply and comfortably; the crossed field covers a large treatment volume with a rotating vector. - Shared contraindications: pacemakers and implanted devices, pregnancy over abdomen or pelvis, carotid sinus region, thrombosis, malignancy and anaesthetic skin. ## Two patients, two machines First patient: day two after knee arthroscopy, aching and reluctant to move. Conventional TENS, electrodes straddling the incision, about 80–100 hertz, 60-microsecond pulses, intensity raised until comfortable paraesthesia — strong but never painful. Thirty-minute sessions, as often as needed, so that analgesia covers the exercise window; relief arrives in minutes and the gate closes again shortly after switch-off, which is exactly why the exercise session is scheduled inside the relief window. Second patient: chronic low back pain with muscle guarding. Acupuncture-like settings — 4 hertz, 200-microsecond pulses, intensity pushed until the lumbar paraspinals visibly twitch — twenty to thirty minutes daily for at least a week before judging effect. Alternatively, interferential: four electrodes in a cross over the lumbar area, carrier 4000 hertz, beat swept between 90 and 130 hertz, amplitude-modulated comfort far above what low-frequency TENS could achieve at depth. Explain to the patient that this mode works more slowly and cumulatively; the ones who expect minute-to-minute relief abandon it prematurely. ## High-yield viva angles Parameter swapping is the standard trap — high-frequency sensory mode versus low-frequency motor mode, with pulse duration and onset time riding each option. Interferential calculations are pure marks: 4000 and 4125 hertz give a 125-hertz beat, and the follow-up asks why 4000 hertz at all (skin impedance falls as frequency rises, so the current enters comfortably and the low-frequency effect is generated in the depths). The naloxone-reversibility of acupuncture-like analgesia is the evidence question examiners reach for when a candidate claims endorphins. ## Frequently asked questions ### What settings define conventional TENS? High frequency (about 50–100 hertz), short pulse duration (50–80 microseconds), strong but comfortable sensory-level intensity. ### How is the beat frequency produced in interferential therapy? By crossing two medium-frequency currents — the beat equals their difference, e.g. 4000 and 4125 hertz giving 125 hertz at depth. ### Which mechanism underlies acupuncture-like TENS, and what reverses it? Beta-endorphin release; naloxone reverses the analgesia, which is the classical supporting evidence. ### Why is interferential current more comfortable at depth than low-frequency current? Medium-frequency carriers meet far less skin impedance, so deeper stimulation is achieved without the surface discomfort. ### Where should TENS electrodes never be placed? Over the carotid sinus, the pregnant uterus, the eyes, broken skin, or anywhere near a pacemaker or implanted device.