# Electrotherapy Basics > Electrotherapy basics in Physiotherapy: current types, pulse parameters, faradic versus galvanic currents, sensory and motor effects, contraindications and safety. - Canonical URL: https://prepelephant.com/topics/allied/physiotherapy/electrotherapy-basics - 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: 2026-2026-10-02 - How to cite: "Electrotherapy Basics", PrepElephant, https://prepelephant.com/topics/allied/physiotherapy/electrotherapy-basics ## Direct answer Faradic for innervated, galvanic for denervated — that one line organises clinical electrotherapy better than any other. Currents are applied to relieve pain (gate control and opiate-mediated mechanisms), to stimulate intact muscle through its nerve, to re-educate weak muscles, to promote tissue healing and to drive drugs across skin by iontophoresis. Every prescription is defined by four parameters — frequency, intensity, pulse duration and duty cycle — and the machine that heals can also harm when contraindications such as pacemakers and pregnancy are ignored. ## What you must remember - Current families: direct current (galvanic, unidirectional, with chemical effects at the electrodes), alternating current (bidirectional, no net chemical effect) and pulsed currents of which faradic-type stimulation is the classic clinical example. - The four dosage parameters — frequency in hertz, intensity in milliamperes, pulse duration in microseconds to milliseconds, and duty cycle (the on–off ratio, commonly 1:5 for muscle work to delay fatigue). - Faradic-type current: short pulses of roughly 0.1–1 millisecond, classically surged at around 50 hertz, producing a tetanic contraction in normally innervated muscle — and nothing useful in denervated muscle. - Denervated muscle must be excited directly with long-duration triangular or exponential pulses, classically tens to hundreds of milliseconds at low frequencies; the triangular shape matters because its slow rise lets nerve fibres accommodate while the slowly responding denervated muscle fibre is still excited. - Gate control theory (Melzack and Wall, 1965): activity in large-diameter A-beta fibres inhibits pain transmission in the dorsal horn — the rationale for sensory-level analgesic currents. - Physiological effects of motor stimulation: the muscle pump improves venous and lymphatic return, disuse atrophy is limited, and wasted activation patterns are re-educated after injury and surgery. - Iontophoresis uses continuous direct current to drive like-charged drug ions into tissue — positively charged drugs under the positive electrode. - Standing contraindications: cardiac pacemakers and implanted electronics, pregnancy over the abdomen and pelvis, active malignancy, deep vein thrombosis, stimulation over the carotid sinus, broken or anaesthetic skin, and undiagnosed pain. ## Matching the current to the patient Three patients, three choices. First, a stroke patient with a dropped wrist but intact innervation: faradic-type neuromuscular electrical stimulation over the wrist extensors, sensory-motor intensity, 20–50 hertz, duty cycle about 1:5, twenty minutes per session — the nerve is present, so short pulses reach it easily. Second, a radial nerve palsy with electromyography-confirmed denervation. Short pulses now achieve nothing, because the target is the muscle membrane itself, which needs durations many times longer — long triangular pulses at very low frequencies. This is the classic exam discrimination, and getting it wrong wastes months of therapy; re-innervation is also monitored with the same electrodiagnostics. Third, a painful post-operative knee needing analgesia alone: sensory-level stimulation, intensity below motor threshold, using the gate mechanism. For each patient the reasoning runs nerve-versus-muscle, strength-versus-sensory threshold, and dose-versus-fatigue. Safety screening is identical for all three — implanted devices, pregnancy, thrombosis, carotid region, skin integrity — and electrodes must sit on clean, healthy skin with good contact gel, never over open wounds or tumours. ## Where students slip The faradic-versus-galvanic indication is the most-scrambled fact in electrotherapy; the cleanest memory hook is that a muscle stripped of its nerve needs direct, long-duration stimulation. Students also swap the duty cycle's purpose (rest periods prevent fatigue, not comfort), assign iontophoresis drugs to the wrong polarity, and quote gate control backwards — large-fibre input closes the gate on pain. Viva panels ask the year and authors of gate control as standard. ## Frequently asked questions ### Why can faradic current not stimulate denervated muscle? Short pulses excite nerve, not muscle membrane; denervated muscle lacks functioning nerve and needs long-duration direct stimulation. ### What is the duty cycle, and why is 1:5 used for muscle stimulation? The on–off ratio of stimulation; the rest phase delays fatigue so a useful contraction lasts the session. ### Which theory explains sensory-level electrical analgesia? Gate control — Melzack and Wall, 1965 — large-diameter afferent activity inhibiting dorsal horn pain transmission. ### Under which electrode is a positively charged drug placed during iontophoresis? The positive (anode) electrode, since like charges repel. ### List the standard contraindications to electrical stimulation. Pacemakers and implanted devices, pregnancy over abdomen or pelvis, malignancy, deep vein thrombosis, carotid sinus area, and anaesthetic or broken skin.