Functional Electrical Stimulation (FES) versus Transcutaneous Electrical Nerve Stimulation (TENS): Evidence‑Based Distinctions

Mechanistic Differences

FES actively contracts paralyzed or weak muscles by delivering motor‑level currents that depolarize peripheral motor nerves, thereby producing functional movements; TENS delivers sensory‑level currents that activate pain‑inhibitory pathways without causing muscle contraction. [1][2]
FES provides proprioceptive feedback that promotes neural reorganization and motor learning, whereas TENS does not supply the proprioceptive input required for motor recovery. [2][3]

Wrist‑drop rehabilitation: Applying FES to wrist‑extensor muscles for 30 minutes three times daily during attempted active extension yields measurable gains in muscle force and motor control.** [1][4]
Foot‑drop after cerebrovascular injury: Combining FES with physical therapy to trigger ankle‑dorsiflexor contraction during the swing phase improves gait speed and walking endurance.** 2
Upper‑extremity motor impairment: EMG‑triggered FES to shoulder musculature enhances motor control and reduces glenohumeral subluxation.** 2
Timing of initiation: FES should be started within the first six months after injury to align with the critical window for motor recovery.** [1][2]4

Electrode placement: Surface electrodes are positioned over the motor points of the target muscle groups (e.g., wrist extensors, ankle dorsiflexors).** [1][2]
Synchronization with intent: Modern FES devices monitor EMG or EEG signals and deliver stimulation only when the patient attempts the corresponding voluntary movement.** (no specific citation)
Integration with task‑specific practice: FES must be paired with intensive, progressive, task‑oriented training; FES alone is insufficient for functional gains.** [1][2]
Duration of therapy: Intervention is typically limited to the first several weeks to months of rehabilitation.** [1][2]

Do not confuse percutaneous tibial nerve stimulation (PTNS) with FES: PTNS is used for pelvic floor disorders and, in one trial, achieved an 82 % response rate with percutaneous electrodes versus 45 % with transcutaneous electrodes and 13 % with sham, highlighting the importance of electrode modality.** [5][3]
Avoid static splinting when FES is appropriate: Prolonged immobilization promotes learned non‑use, muscle deconditioning, compensatory movement patterns, and poorer functional recovery.** 1
Guideline recommendation: The American Stroke Association advises using FES combined with active exercise rather than immobilization for severe wrist‑drop.** 1
If a removable splint is required for positioning, monitor closely and discontinue if pain or skin breakdown occurs. 1

Indications: Primarily employed for mild‑to‑moderate musculoskeletal pain, neuropathic pain, and as adjunctive analgesia (e.g., diabetic peripheral neuropathy).** (no cited source)
Protocol characteristics: Electrodes target sensory nerve pathways; stimulation is continuous or intermittent and does not require the patient’s active movement participation.** (no cited source)

For patients with radial nerve palsy, functional electrical stimulation should be delivered using tetanic frequencies between 25 Hz and 75 Hz with pulse durations of ≥ 0.5 ms to achieve effective muscle contractions. 6

Stimulation intensity should be set to the maximum tolerable level, beginning at a low level during initial sessions to avoid muscle damage, and progressively increased whenever possible. 6

Each stimulation burst should have an on‑time of at least 4 seconds to generate sufficient force for functional wrist‑extension movements. 6

Sessions should be scheduled 2–3 times per week, providing adequate time for muscle regeneration between treatments. 6

Pulse durations of 200–500 µs minimum are recommended, with longer pulses up to 1 ms producing stronger muscle contractions and less discomfort. 7
Tetanic stimulation frequencies in the range of 25–75 Hz are optimal for generating functional wrist‑extensor contractions; broader neural stimulation applications commonly use 10–300 Hz depending on therapeutic goals. 8

Electrodes should be positioned proximal on the extensor surface of the forearm, over the motor points of the wrist‑extensor muscles, to maximize torque, minimize required current intensity, and reduce patient discomfort. 7
Carbonized rubber electrodes provide the highest evoked torque when used with conductive gel and secure fixation (e.g., tape or Velcro). 7
Larger surface‑area electrodes activate a greater cross‑section of muscle tissue, yielding higher force output at comparable comfort levels. 7

A charge‑balanced biphasic waveform with a leading cathodic phase is recommended to achieve reliable membrane depolarization while maintaining patient comfort. 8
Current‑controlled stimulation is essential to ensure consistent charge delivery despite variations in tissue impedance. 8
For surface electrodes, maintain a charge density below 30 mC/cm² to prevent tissue injury. 9

Stimulation intensity should be titrated to the maximum tolerable level, beginning with low amplitudes during the first 2–5 sessions to avoid muscle damage and delayed‑onset soreness. 7
Higher currents are necessary to recruit a larger proportion of muscle fibers and enhance training effectiveness, though exact amplitude values must be individualized because of differences in skin impedance, subcutaneous tissue, and nerve anatomy. 7