Baseline Pain Signaling
Pain fibers reach the dorsal horn completely unopposed.
- 5–30: A-delta conduction speed (m/s, sharp pain)
- 0.5–2: C-fiber conduction speed (m/s, dull pain)
- 0%: Gate closure (no competing input)
- 0%: Reported relief (no intervention active)
Nociceptor activation
Tissue injury fires small-diameter pain afferents directly.
Dorsal horn relay
Pain fibers synapse onto spinal projection neurons unchecked.
Without competing input, the pain gate stays fully open.
Ascending transmission
Projection neurons carry the signal upward to the brain.
Electrode Placement
Correct pad position determines which fibers get recruited.
- 2–4: Typical electrode spacing (cm apart)
- Superficial: Target depth (large myelinated fibers)
- 1–3: Skin impedance (kΩ typical)
- Standby: Device status (output not yet active)
Pad positioning
Electrodes sit along the painful dermatome or nerve trunk.
Circuit formation
Current will flow between the anode and cathode pads.
Placement over the nerve path is critical for fiber recruitment.
Fiber selectivity
Large A-beta fibers activate before small pain fibers.
Low-Frequency Stimulation
Slow pulses recruit the body's own opioid release system.
- 1–10: Typical frequency (Hz, low-rate TENS)
- 20–40: Onset time (minutes, slower)
- Endorphin: Mechanism (release, opioid-mediated)
- Longer: Relief duration (lasting after session ends)
Motor-level pulses
Low-rate stimulation triggers rhythmic muscle twitching.
Descending inhibition
Midbrain circuits release endorphins into the spinal cord.
Naloxone can block this pathway, confirming opioid involvement.
Slower onset
Relief builds gradually over tens of minutes.
High-Frequency Stimulation
Fast pulses close the spinal gate almost immediately.
- 50–150: Typical frequency (Hz, conventional TENS)
- Seconds: Onset time (to minutes, rapid)
- Gate control: Mechanism (Melzack-Wall theory)
- Shorter: Relief duration (fades after stimulation stops)
A-beta recruitment
High-rate pulses preferentially fire large touch fibers.
Interneuron activation
A-beta input excites the inhibitory gate-control interneuron.
The interneuron presynaptically inhibits incoming pain signals.
Signal blockade
Pain-fiber transmission to projection neurons is suppressed.
Optimized Parameters
Combining both pathways maximizes measured pain relief.
- 80–120: Optimal frequency band (Hz, patient-tuned)
- Strong, tolerable: Optimal intensity (sub-motor threshold)
- Up to 90%: Combined relief (gate plus endorphin)
- Managed: Tolerance risk (by parameter cycling)
Dual-pathway tuning
Alternating frequencies engage gate and endorphin mechanisms.
Intensity titration
Strong but comfortable intensity maximizes fiber recruitment.
Individualized titration outperforms fixed default settings.
Sustained outcome
Optimized settings sustain relief with minimal tolerance.