Is functional electrical stimulation (FES) similar to a transcutaneous electrical nerve stimulation (TENS) device?

FES and TENS Are Fundamentally Different Technologies

No, functional electrical stimulation (FES) is not similar to a TENS device—they serve entirely different purposes and use distinct mechanisms. FES actively contracts paralyzed or weak muscles to restore lost motor function, while TENS delivers sensory-level stimulation primarily for pain relief without producing functional muscle contractions. 1, 2, 3

Core Mechanistic Differences

FES (Functional Electrical Stimulation)

• Produces forceful muscle contractions by directly stimulating intact peripheral motor nerves to activate paralyzed or paretic muscles, creating coordinated functional movements 3, 4
• Restores skeleto-motor functions such as wrist extension, grasping, walking, and other purposeful movements that patients cannot perform voluntarily 3, 5
• Requires motor-level current intensity sufficient to depolarize motor nerves and generate visible, functional muscle contractions 4, 6
• Promotes neural reorganization by providing proprioceptive feedback to the central nervous system during active muscle contraction, facilitating motor learning and recovery 2

TENS (Transcutaneous Electrical Nerve Stimulation)

• Delivers sensory-level stimulation designed to activate pain-inhibitory pathways without producing muscle contractions 7
• Primary purpose is analgesia through segmental inhibition of pain signals in the spinal cord dorsal horn and activation of descending inhibitory pathways with endogenous opioid release 7
• Uses sub-motor threshold currents that create tingling or buzzing sensations but do not cause functional muscle contractions 7
• Does not restore motor function or provide the proprioceptive feedback necessary for motor recovery 8, 7

Clinical Applications Highlight the Distinction

When FES Is Indicated

• Wrist drop from radial nerve injury or stroke: FES applied to wrist and forearm extensors for 30 minutes three times daily during active wrist extension attempts produces measurable increases in muscle force and motor control 1, 9
• Foot drop after stroke: FES combined with physical therapy improves gait speed and walking endurance by actively contracting ankle dorsiflexors during the swing phase of gait 2
• Upper extremity motor impairment: FES triggered by electromyography improves motor control at the shoulder and reduces glenohumeral subluxation 2
• Must be initiated within 6 months post-injury to align with the critical window for motor recovery 1, 2, 9

When TENS Is Used Instead

• Mild to moderate musculoskeletal pain where pain relief rather than functional restoration is the goal 7
• Neuropathic pain conditions where sensory modulation of pain pathways is therapeutic 7
• Adjunctive analgesia in conditions like diabetic peripheral neuropathy 7

Evidence-Based Treatment Protocols Differ Completely

FES Protocol Requirements

• Surface electrodes positioned over target motor points of wrist extensors, ankle dorsiflexors, or other paralyzed muscle groups 1, 2
• Stimulation synchronized with motor intention: Modern FES devices monitor EMG or EEG signals to trigger stimulation when the patient attempts voluntary movement 5, 6
• Combined with intensive task-specific practice: FES alone is insufficient—it must be paired with active motor practice and progressive resistance training 1, 2
• Time-limited intervention: Typically used during the first several weeks to months of rehabilitation 1, 2

TENS Protocol Characteristics

• Electrodes placed to target sensory nerve pathways rather than motor points 7
• Continuous or intermittent sensory stimulation without regard to voluntary motor effort 7
• No requirement for active patient participation in movement during stimulation 7

Critical Clinical Pitfalls

Do Not Confuse Percutaneous Tibial Nerve Stimulation (PTNS) With FES

• PTNS can be delivered via transcutaneous (skin-surface) or percutaneous (needle) electrodes for conditions like fecal incontinence, but this represents a distinct application from motor restoration 8
• In one trial, percutaneous stimulation achieved 82% response rate versus 45% for transcutaneous and 13% for sham, demonstrating that electrode placement and stimulation parameters matter profoundly 8

Avoid Static Splinting When FES Is Appropriate

• Static wrist splinting promotes learned non-use, muscle deconditioning, compensatory movement patterns, and poorer functional recovery 1
• The American Stroke Association recommends FES combined with active exercise rather than immobilization for severe wrist drop 1
• If a removable splint is necessary for positioning, monitor closely and discontinue if pain or skin breakdown occurs 1

Bottom Line for Clinical Practice

FES is a motor-restoration technology that contracts muscles to restore function, while TENS is a sensory-modulation technology for pain relief. 3, 4, 7 They are not interchangeable, and selecting the wrong modality will fail to address the patient's primary deficit—whether that is lost motor function requiring FES or pain requiring TENS.