Is a functional electrical stimulation protocol using two surface electrodes, a 100‑µs pulse width, biphasic waveform, for five minutes appropriate for treating my radial nerve palsy?

Your Protocol Needs Significant Modification for Radial Nerve Palsy

Your proposed protocol of 100 µs pulse width and 5-minute duration is inadequate for functional electrical stimulation in radial nerve palsy—you need pulse widths ≥500 µs (0.5 ms), stimulation frequencies of 25-75 Hz, on-times of at least 4 seconds per burst, and session durations of 30 minutes, 2-3 times per week. 1

Critical Parameter Corrections

Pulse Width (Duration)

• Your 100 µs is far too short. The evidence clearly indicates pulse durations should range from 200-500 µs minimum, with longer durations up to 1 ms producing stronger contractions and less pain 2
• For radial nerve palsy specifically, pulse widths must be ≥500 µs (0.5 ms) to achieve effective muscle contractions in wrist extensors 1
• A recent study on wrist/finger extensors found that introducing a 100 µs interphase interval (the gap between biphasic phases) enhanced force production, but this is separate from the actual pulse width 3

Session Duration

• Five minutes is grossly insufficient. FES for wrist-drop rehabilitation requires 30-minute sessions, three times daily during attempted active extension to yield measurable gains in muscle force and motor control 1
• The evidence consistently shows that adequate stimulation time is necessary for therapeutic benefit—brief 5-minute sessions will not provide the proprioceptive feedback required for motor recovery 1

Stimulation Frequency

• Your protocol doesn't specify frequency, but you need tetanic frequencies between 25-75 Hz to produce functional muscle contractions 1
• Typical neural stimulation applications use repetition rates of 10-300 Hz, with the specific range depending on the therapeutic goal 2

On-Time Per Burst

• Each stimulation burst should have an on-time of at least 4 seconds to generate sufficient force for functional wrist-extension movements 1
• This is distinct from total session duration—you need repeated 4-second contractions throughout the 30-minute session

Electrode Configuration (Your Two-Electrode Setup)

Electrode Placement

• Position both electrodes proximally over the extensor surface of the forearm, just distal to the common extensor origin, rather than using a distal placement 3
• This proximal placement provides more comfortable stimulation sensation while maintaining effective force production 3
• Electrodes should be positioned over motor points to maximize muscle tension, minimize current intensity, and reduce discomfort 2

Electrode Type and Size

• While most studies use self-adhesive surface electrodes, carbonized rubber electrodes produce the highest evoked torque but require conducting gel and securing with tape or Velcro 2
• Larger electrodes stimulate greater muscle cross-sectional area and produce more force at a given discomfort level 2

Waveform Specifications

Biphasic Configuration

• Your "B mode" (biphasic) is correct—use a charge-balanced biphasic waveform with a leading cathodic phase to elicit membrane depolarization, followed by an equal-charge anodic phase 2
• Consider adding a 100 µs interphase interval between the cathodic and anodic phases to enhance force production without increasing discomfort 3
• Asymmetric balanced biphasic square waveforms are perceived as comfortable and clinically effective for wrist flexor and extensor muscles 4

Intensity and Progression

Current Amplitude

• Stimulation intensity should be set to the maximum tolerable level, though you should begin at low levels during the first 2-5 sessions to avoid muscle damage and delayed-onset muscle soreness 2, 1
• High currents are necessary to maximize recruited muscle fibers and training effectiveness 2
• No universal current amplitude guidelines exist due to individual differences in skin impedance, subcutaneous fat thickness, and nerve branch location 2

Treatment Schedule and Timing

Frequency of Sessions

• Schedule sessions 2-3 times per week to provide adequate time for muscle regeneration between treatments 1
• This differs from the acute stroke recommendation of three times daily—radial nerve palsy protocols are less intensive 1

Critical Window

• FES should be initiated within the first 6 months after injury to align with the critical window for motor recovery 1, 5
• Strong evidence supports efficacy for individuals less than 6 months post-injury 5

Integration with Active Therapy

Essential Combination

• FES must be paired with intensive, progressive, task-oriented training—FES alone is insufficient for functional gains 1
• Apply FES during attempted active wrist extension movements to provide proprioceptive feedback that promotes neural reorganization and motor learning 1, 5
• Modern FES devices can monitor EMG signals and deliver stimulation only when you attempt voluntary movement 1

Common Pitfalls to Avoid

Do Not Use TENS Instead

• Do not confuse transcutaneous electrical nerve stimulation (TENS) with FES—TENS delivers sensory-level currents for pain management without causing muscle contraction and does not provide the proprioceptive input required for motor recovery 1

Avoid Static Splinting

• Prolonged immobilization promotes learned non-use, muscle deconditioning, and compensatory movement patterns 1
• The American Stroke Association advises using FES combined with active exercise rather than immobilization for severe wrist-drop 1

Safety Considerations

• Current-controlled stimulation protocols are essential to ensure reproducible charge delivery despite variations in tissue impedance 2
• For surface electrodes with typical geometrical surface areas, maintain charge density below 30 mC/cm² to avoid tissue damage 2