Electrical Stimulation

Teknologier til behandling: Elektriske stimulationer 

Teknologi i sundhedssektoren 

KVT, 1. sem., AAU 

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Contents 

What can we use electrical stimulations for? 

Basic principles 

Recovery of movements 

TENS 

Upper limb 

Lower limb 

Muscle stimulation 

Reflex stimulation

Electrical Stimulation: Neural Prostheses 

CONTROL OF TREMOR 

ACTIVATION OF MUSCLES AFTER 

RECONSTRUCTIVE TONGUE SURGERY 

PHRENIC PACING 

CONTROL OF ARM/HAND: 

REACHING AND GRASPING 

CORRECTION OF SCOLIOSIS 

PRESSURE SORE RELIEF 

MUSCLE EXERCISING 

CONTROL OF LEGS: STANDING 

AND WALKING 

CONTROL OF EPILEPSY 

REDUCTION OF SPASTICITY 

RESTORATION OF VISION 

RESTORATION OF HEARING (COCHLEAR IMPLANT) 

REDUCTION OF SNORING AND SLEEP APNEA 

CARDIAC PACING 

NERVE REGENERATION 

BOWEL EMPTYING 

BLADDER EMPTYING AND CONTROL 

OF INCONTINENCE 

ELECTROEJACULATION 

WOUND HEALING 

PAIN SUPRESSION 

RESTORATION OF SENSORY 

FUNCTION


A neural prostheses is a system for replacing or augmenting a function that 

is lost or diminished because of the injury or disease of the nervous system. 

The basic principle for operation of a neural prosthesis is the 

activation/stimulation of sensory-motor mechanisms. 

Functional Electrical Stimulation (FES) elicits controlled neural activation by 

delivering low level electrical currents. 

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Electrical Stimulation 

Neural Prosthesis 

Principle of functioning 

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Electrical Stimulation- Basic principles 

Excitation of neuromuscular tissue 

Stimulation parameters 

Modalities of stimulation 

nerve-muscle stimulation 

reflex stimulation 

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Excitation of neuromuscular tissue 

Stimulating current Neural excitation Action potential Impulses 

propagate from stimulation site 

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Factors determining neural excitation 

Parameters of the stimulus 

Electrode/tissue impedance 

Size and location of the electrodes 

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Recruitment of nerve fibers by changing the stimulation amplitude 

Closest and largest fibers are 

activated 

Also smaller close fibers and 

larger distant fibers are activated 

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Variation of amplitude and pulse duration required for excitation 

Current intensity (mA) 

Near maximal 

Threshold 

Pulse duration (µs) 

The motor response can be controlled by changing the pulse 

intensity and/or duration 

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Variation of frequency (pulse repetition rate) 

The frequency of the stimulus influences the strength and quality 

of the evoked motor response 

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Stimulation frequency & Fatigue 

The rate at which muscle fatigues during sustained contraction is affected by the 

stimulation frequency 

Frequency Fatigue 

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Stimulation waveforms 

Monophasic (unidirectional) ion flow in one direction 

Asymmetric biphasic (bidirectional) ion flow in both directions 

Symmetric biphasic (bidirectional) allows both electrodes to depolarize the 

neural membrane 

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Current takes the pathway of least resistance 

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1) The skin is a good insulator 

Current takes the pathway of least resistance 

2) Tissue impedance is related to water content 

3) Adipose tissue acts as an insulator 

4) Muscle tissue conducts current better in the 

longitudinal direction 

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Electrode size determines current density 

+ - 

Nerve 

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Electrical Stimulation for Recovery of Movement 

Electrode location Motor points 

Motor point: the point on a muscle that provides the greatest motor 

response with the minimal stimulating current 

 

Corresponds anatomically with the motor end plate 

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Nerve-Muscle stimulation 

Primary target: motor nerves 

Result: excitation of efferent nerve fibers 

(also afferent fibers) 

 

Muscle contraction 

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Reflex stimulation 

Primary target: cutaneous sensory nerves 

Result: excitation of afferent nerve fibers 

eliciting the withdrawal reflex 

 

Muscle contraction 

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Production of movements - Summary 

Different movements Voluntary production 

Contraction strength 

Healthy people People with paresis / paralysis 

Placement of stimulation 

electrodes 

Summation Stimulus frequency 

Recruitment Stimulus intensity / duration 

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Upper limb – Surface electrodes 

It is impossible to generate a replica of able-bodied movements with surface electrodes, 

especially after CNS injury or disease. It is only important to generate movements that 

are appropriate for regaining the lost function. 

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Electrical Stimulation of Muscles 

Upper limb – Permanent use 

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Upper limb – Therapeutic use (FET) 

FET: Paretic subjects are required to exercise functional tasks. This exercising 

is assisted with a neural prosthesis that controls the opening, grasping, 

holding, and releasing functions of selected objects typical for normal daily 

activities. 

The patterned electrical stimulation is programmed to control flexor and 

extensor muscles in a manner that mimics able-bodied opening/closing, and 

opening/releasing synergies. 

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The FET tasks are to actively reach and grasp/release different objects (e.g., can, 

telephone receiver, pen, comb, toothbrush). The treatment consists of daily, 30-minute 

long sessions, during three consecutive weeks. 

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0 weeks after 3 weeks 

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0 weeks after 3 weeks 

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Lower limb – Permanent use 

Single channel stimulation for correcting drop foot 

Walk-Aid (left), a single-channel, self-contained stimulator to correct foot-drop problem 

(Adapted from Da Silva et al.,1997). The mounting shell is easy to model to the leg 

shape and it comprises sensors, electrodes, stimulator and the battery. The KDC 2000A, 

Cotas, DK (right) peroneal stimulator to correct foot-drop problems. 

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Lower limb – Permanent use – Surface stimulation 

Walking with single-channel FES system for correction of drop foot. 

Popovic et al., Zurich, 2001 

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Lower limb – Permanent use – Implantable electrodes 

1 . T h e i m p l a n t 

a . D i g i t a l 4 - c h a n n e l n e r v e s t i m u l a t o r 

I m p l a n t e d u n d e r t h e s k i n a n d c o n t a i n s t h e 

e l e c t r o n i c c i r c u i t r y a n d t h e r e c e i v i n g a n t e n n a 

f o r p o w e r a n d c o n t r o l . 

b . M u l t i - l e a d c a b l e s w i t h i n - l i n e c o n n e c t o r 

c . T h e 1 2 c o n t a c t e l e c t r o d e c u f f 

P l a c e d a r o u n d t h e p e r o n e a l n e r v e a t a p l a c e 

w h e r e t h e n e r v e c o n t a i n s a l m o s t a l l n e r v e 

f i b e r s g o i n g t o t h e m u s c l e s t h a t l i f t t h e f o o t . 

P e r o n e a l 

n e r v e 

A n k l e 

d o r s i f l e x o r 

m u s c l e ( s ) 

2 . P r o g r a m m a b l e s t i m u l u s c o n t r o l a n d p o w e r u n i t 

C o n t a i n s m i c r o c o n t r o l l e r a n d i n d u c t i v e t r a n s m i t t e r f o r p o w e r i n g 

a n d c o n t r o l l i n g t h e i m p l a n t ( 1 ) . 

P r o g r a m m a b l e v i a a P C f o r o p t i m a l f u n c t i o n a l i t y . 

T h e u n i t i s s m a l l e n o u g h t o f i t i n t o a p o c k e t a n d i s p o w e r e d b y a 

r e c h a r g a b l e b a t t e r y . 

3 . H e e l s w i t c h 

W h e n t h e f o o t i s l i f t e d f r o m t h e g r o u n d t h e 

h e e l s w i t c h s i g n a l s t h i s ( b y w i r e o r w i r e l e s s ) 

t o t h e e x t e r n a l c o n t r o l u n i t ( 2 ) . 

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B 

D 

A 

An implantable stimulator (D) (Ljubljana, Slovenia) comprising: a heel switch (A), 

an external stimulator with a single AA battery, an emitting RF-antenna (B); and 

the implant receiver-electrodes (C) that is attached to the common peroneal 

nerve. 

C 

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Actigait®, Neurodan, DK – implantable multichannel drop foot system using a 

multi-contact cuff interface 

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Electrical Stimulation – Reflex activation 

Lower limb – Surface stimulation 

Reflex stimulation during the swing phase of the gait cycle 

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The nociceptive withdrawal reflex (NWR) 

The NWR is a polysynaptic spinal 

reflex intended to protect the body 

from damaging stimuli. 

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The nociceptive withdrawal reflex (NWR) 

Painful electrical stimulation 

1 ms 

200 Hz 

It evokes a short lasting, sharp, 

pinpricking sensation at the stimulation site 

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Single stimulus vs. repetitive stimulation 

Ankle joint kinematics – healthy subjects – sitting position 

20 degrees 

-10 

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Effect of stimulating during gait 

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Clinical study to test whether FET based on reflex activation, applied in 

acute hemiplegic patients during gait training produces greater 

improvement in gait function than intensive gait training alone. 

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Inclusion test 

Stand and walk without therapist’s support



Training session 

Without stimulation With stimulation 

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Before 

After 

Evaluation sessions 

Control Treatment 

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Increment in FAC test's level 

4 

3 

2 

1 

0 

General walking condition: Functional Ambulation Category Test 

Control 

Treatment 

FAC test 

Before After 1 m. after 6 m. after 

* 

Evaluation session 

FAC Test 

0: Patient can not walk or needs 

help from 2 or more therapists 

1: Patient needs constant help from 

one therapist for weight support and 

balance 

2: Patient needs constant or 

intermittent help from a therapist to 

keep balance and coordination 

3: Patient needs verbal guidance 

4: Patient needs help for stairs or 

uneven ground 

5: Patient walks alone 

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TENS: Transcutaneous Electrical Nerve Stimulation 

Transcutaneous electrical nerve stimulation (TENS) is a simple, noninvasive 

analgesic technique that is used extensively in health-care settings. 

It can be administered in the clinic by healthcare professionals or at home 

by patients who have a TENS device. 

TENS is mainly used for the symptomatic management of acute and 

nonmalignant chronic pain. It is also claimed that TENS has tissue-healing 

effects although it is used less often for these actions. 

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Analgesic effects of TENS (Claims!) 

Relief of acute pain 

Postoperative pain 

Labor pain 

Dysmenorrhoea 

Musculoskeletal pain 

Bone fractures 

Dental procedures 

Relief of chronic pain 

Low back pain 

Arthritis 

Stump and phantom pain 

Postherapeutic neuralgia 

Trigeminal neuralgia 

Peripheral nerve injuries 

Angina pectoris 

Facial pain 

Metastatic bone pain 

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Non-Analgesic effects of TENS (Claims!) 

Postoperative nausea associated with opioid medication 

Nausea associated with chemotherapy 

Morning sickness 

Motion/travel sickness 

Improving blood flow 

Reduction in ischemia after reconstructive surgery 

Reduction of symptoms associated with diabetic neuropathy 

Improved healing of wounds and ulcers 

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TENS: The Pain Gate 

Under normal physiological circumstances, the brain generates pain 

sensations by processing incoming noxious information arising from stimuli 

such as tissue damage. 

In order for noxious information to reach the brain it must pass through a 

metaphorical ―pain gate‖ located in lower levels of the central nervous 

system. The hypothesis is that TENS ―closes‖ the Pain Gait. 

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TENS: dosage 

Clinical trials report that maximum pain relief occurs when the TENS device is 

switched on and that the analgesic effect usually disappears quickly once the device 

is switched off. 

Long-term users of TENS: 75% used TENS on a daily basis and 30% reported using 

TENS for more than 49 hours a week. 

Monitor skin condition under the electrodes on a regular basis and take regular 

(although short) breaks from stimulation! 

Some patients report post stimulation analgesia lasting between 18 and 2 hours 

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TENS: Electrode positions for common pain conditions—anterior view. 

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TENS: Electrode positions for common pain conditions—posterior view. 

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TENS: Contraindications 

People suffering from epilepsy 

Women in the first trimester of pregnancy. However, TENS is routinely 

administered on the back to relieve pain during labor 

Patients with cardiac pacemakers: this is because the electrical field generated by 

TENS could interfere with implanted electrical devices. 

Undiagnosed pain (unless recommended by a medical practitioner) 

People with heart disease (unless recommended by a cardiologist) 

Do not apply TENS: over the carotid sinus, on broken skin, and internally 

(mouth) 

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CONTROL OF TREMOR 

ACTIVATION OF MUSCLES AFTER 

RECONSTRUCTIVE TONGUE SURGERY 

PHRENIC PACING 

CONTROL OF ARM/HAND: 

REACHING AND GRASPING 

CORRECTION OF SCOLIOSIS 

PRESSURE SORE RELIEF 

MUSCLE EXERCISING 

CONTROL OF LEGS: STANDING 

AND WALKING 

CONTROL OF EPILEPSY 

REDUCTION OF SPASTICITY 

RESTORATION OF VISION 

RESTORATION OF HEARING (COCHLEAR IMPLANT) 

REDUCTION OF SNORING AND SLEEP APNEA 

CARDIAC PACING 

NERVE REGENERATION 

BOWEL EMPTYING 

BLADDER EMPTYING AND CONTROL 

OF INCONTINENCE 

ELECTROEJACULATION 

WOUND HEALING 

PAIN SUPRESSION 

RESTORATION OF SENSORY 

FUNCTION 

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Electrical Stimulation

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