TENS (transcutaneous electrical nerve stimulation): pain modulation modality. Two main modes - 1) Conventional/sensory TENS - high frequency (50-150 Hz), low intensity (sensory comfortable level), short pulse duration (50-100 µs); activates large-diameter A-beta fibers, gate control mechanism (Melzack-Wall theory), rapid onset, short duration; 2) Acupuncture-like/motor TENS - low frequency (1-10 Hz), high intensity (motor contraction level), wider pulse (200-300 µs); endogenous opioid release, slower onset, longer duration. Burst TENS combines both. Indications - chronic and acute pain, postoperative pain, labor analgesia, dysmenorrhea, neuropathic pain. Contraindications - cardiac pacemaker (relative), pregnancy abdomen/lumbar (relative), broken skin, malignancy site. Daily 30-60 min sessions; outcome via NRS.
NMES and FES (neuromuscular and functional electrical stimulation): NMES uses higher intensity to elicit muscle contraction. Parameters - 30-50 Hz frequency, 200-400 µs pulse duration, on:off ratio 5-10:50, intensity to produce strong but tolerated contraction. Indications - muscle strengthening in weakness (post-surgical, immobilization atrophy), neurologic injury (incomplete SCI, stroke), preventing disuse atrophy, knee/quad rehabilitation, urinary incontinence, dysphagia. FES applies NMES during functional movement (gait, reach, grip) to assist task performance and promote motor learning; emerging in stroke and SCI rehabilitation. Russian current (medium-frequency 2500 Hz with 50 Hz burst) for muscle strengthening - high tolerance, deep penetration. Contraindications - implanted cardiac devices, denervated muscle (LMN injury), epilepsy.
Other modalities and parameter selection: 1) Interferential current (IFC) - two medium-frequency currents (4000 Hz with carrier modulation creating beat frequency 1-150 Hz at intersection); deeper penetration than TENS, comfortable, used for deep pain (knee, shoulder, low back); premodulated and quadripolar setups; 2) High-voltage pulsed current (HVPC) - very short twin-pulse, high voltage; used for wound healing (especially pressure ulcers, diabetic ulcers), edema reduction; polarity-specific effects; 3) Microcurrent (MENS) - subthreshold current (<1 mA); claimed effects on tissue healing, fracture, wound healing; modest evidence; 4) Diadynamic currents - rectified low-frequency for pain; 5) Iontophoresis - direct current to drive ions of medication into tissue (dexamethasone for tendinopathy, lidocaine for analgesia). Parameter selection guidelines - pulse frequency dictates fiber recruited (high for sensory, mid for muscle, low for opioid); pulse duration dictates depth (longer = deeper); intensity dictates fiber type (higher recruits motor); session duration 15-60 min based on goal.