Neuromuscular Electrical Stimulation (NMES)

Mohammed TA, Omar, Ph.D. PTRehabilitation Health Sciences

Neuromuscular Electrical Stimulation (NMES)

Neuromuscular electrical nerve stimulation (NMES) is electrical Stimulation of The Excitable Tissue (Nerve & Muscle) Using Surface Electrodes to Induce Muscle Contraction Aiming to.

Muscle re-education Prevention/Retardation of disuse atrophy Muscle strength/endurance Muscle pump contractions Increasing range of motion Reducing edema

What is the Motor Point? A point on the skin where an electrical stimulus will cause the maximum contraction of an underlying muscle.

Area of greatest excitability on the surface of the skin overlying superficial muscles that can produce maximum contraction with minimum amount of current intensity.

Motor point is the region in muscle where a great density of terminal motor end plates is found near the surface.

The point where the motor nerve enters the muscle.

Motor point lies at muscles belly between the proximal one third and distal 2/3 of muscle belly or fleshy part of the muscle fibers.

To trace motor point

1. Interrupted direct current at 1ms (1000µs) for innervated muscle

2. Interrupted direct current at 100ms for denervated muscle

What is the Motor Point?To trace motor point

1. Interrupted direct current at 1ms (1000µs) for innervated muscle

2. Interrupted direct current at 100ms for denervated muscle

Position of the MP of quadriceps and gastrocnemii

Chart for Motor Point

Clinical practice

ES parameters

F(1-2Hz)

Intensity (start 1mA)

Pulse duration 100-200µseconds

Pen electrodes (active)

Dispersive electrode

Alcohol swap (cotton) and markers

A, B, C, D, http://www.youtube.com/watch?v=ltQTB5ekhf4

Motor unit It is a single motor neuron (alpha motor neuron from anterior horn cell and all the muscle fibers it stimulate.Each motor unit supplies from 4-100 muscles fibers. Dependent on movement precisions e.g. Gastrocnemius 2,000 muscle fibers per motor neuronMotor neuron determines fiber type.

WWhat is the Motor hat is the Motor UnitUnit??

WWhat is the Motor hat is the Motor UnitUnit??

Sensory Nerve ImpulsesWhen sensory nerve is stimulated the downward traveling impulse has

no effect, while the upward traveling impulse is appreciated at the conscious level of the brain.

Orthodromic propagation: is propagation of nerve impulse toward the sensory cortex.

Antiodromic propagation: is propagation of nerve impulse toward the periphery (sensory receptors on the skin).

Long pulse duration ≥ 10ms (comfortable stabbing sensation). Short pulse duration of ≤ 1ms (mild/moderate prickling sensation).

Motor Nerve Impulses

When motor nerve is stimulated the upward traveling impulse is unable to pass the first synapse, while downward traveling impulse passes to the muscles supplied with that nerve causing the contraction.

Antidromic Propagation: it is a propagation of nerve impulse proximally toward the CNS.

Orthdromic Propagation: it is a propagation of nerve impulse periphery toward neuromuscular junction.

When a stimulus is applied to nerve trunk, or innervated muscle impulse pass to all the muscles that nerve supplies below the point at which it is stimulated, causing them to contract.

Strength Duration Curve (SD)

The SD curve is a graph representation of a quantitieves non liner relationship between intensity and duration of current to

determine whether a muscle is innervated, or denervated.

It depends on; Numbers of motor units recruitment Intensity of current. Frequency Placement of electrodes.

Strength Duration Curve (SD)

Rheobase is a minimal intensity of the current required to produce a minimal visually perceptible muscle contraction (300ms).

Normal values of Rheobase are (2-18mA, 5-35volts)

Chronaxie is a minimal pulse duration required to produce a minimal perceptible response in a muscle, at twice the intensity of rheobase.

Chronaxie of innervated muscles is less than 1ms (range 0.05-0.5ms). Chronaxie of fully denervated muscle may be 30 to 50 ms

Denervated Muscles;

Muscles that have loss nerve supply.

Deneravtion ranges from complete denervation (CD) to partial deneravation (PD).

Complete denervation (CD), all motor unit loses all innervation Partial denervation (PD) some of motor unit in the muscles lose its innervation

Results in Atrophy or Wasting

Muscle atrophy is a reduction in size of muscles (disease/ disuse).

Muscle wasting is the unintentional loss of 5–10% of muscle mass.

Normal Innervation: All nerve fibers supplying the muscle are intact

Stimulation of Denervated Muscles

Physiological & chemical characteristics of denervated muscles

Long Duration Interrupted direct current (LIDC) Current parameters and specifications Effect of ES on denervated muscles

Physiological &chemical Characteristics of Denervated Muscles

Decrease size, and diameter of muscles fibers. Decrease amount of tension generated Increase time required for contraction

Degenerative changes progress until muscle is reinnervated by axons regenerating across site of lesion (2-6months)

If reinnervation does not occur within 2 years fibrous connective tissue replaces contractile elements and recovery of muscle function is not possible

EFFECTS of DENERVATION in SKELETAL MUSCLES

1. Paralysis (immediately):2. Fasiculation (immediately): spontaneous firing of the

injured axon, causing twitching of motor units.3. Fibrillation (days) : spontaneous twitching of individual

muscle fibers due changes in muscle excitability (e.g., Na channels)

4. Muscle atrophy (>1 week):5. Receptiveness to innervation: allows reinnervation of

the muscle by motor axons

Long Duration Interrupted Direct Current

Pulse duration

Inter-PulseInterval Frequency

Long pulse duration (100ms-600ms)100-300ms PD ≥ 300ms CD

3-5times of pulse duration.

Depends on pulse duration e.g. If Pulse duration = 100msFrequency of 1.5 Hz.

Waveforms shape: Saw-tooth, Triangular, & Trapezoid

Unidirectional, interrupted direct current with following characteristic;

Stimulating Denervated Muscle

First 2 weeks.◦ Use asymmetric, biphasic waveform and pulse duration < 1 ms

After 2-3 weeks, ◦ Interrupted DC square wave with long pulse duration > 10 ms, ◦ AC sine wave with frequency < 10 Hz

Inter-Pause interval 3 to 5 times longer (about 3-6 seconds) than stimulus duration to minimize fatigue.

Use monopolar or bipolar electrode setup with small diameter active electrode placed over most electrically active point.

Stimulation using 3 sets of 5 -20 repetitions, 3/ per week

Effects of LIDC

Neuropraxia100ms, rectangular

Axonotmesis100-600ms,

triangular, trapezoidal

Neurotmesis100-2000ms

triangular, saw-tooth

Effect of ES on Denervated Muscles

Retardiation of denervated atrophy Utilization of substrates Prevent venous & lymphatic stasis Working hypertophy Maintenance of muscle extensibility

NMES- Faradic Current

Faradic Current Stimulation

Faradism is unevenly alternating current with each cycle consisting of two unequal phases, with frequency 1-

150Hz. B-Negative: Low intensity long duration

A-Positive: High intensity short durationAA

BB

Faradic Current StimulationFaradic current is a short-duration interrupted Surged direct current with a pulse duration of 0.1 to 1ms, and frequency of 30 -100Hz

Faradic Current StimulationFaradic current is a short-duration interrupted Surged direct current with a pulse duration of 0.1 to 1ms, and frequency of 30 -100Hz

Physiological Effects of Faradic Stimulation

Sensory nerves Mild prickling due to stimulation of

sensory nerve .

Mild erythema due to local reflex vasodilatation of superficial blood

vessels, which causes slight reddening of the superficial tissues.

Motor nerves

Faradic current stimulates the motor nerves /muscle, causes contraction

of the muscles.

Because the stimuli repeated 50 times (50Hz) or more, the

contraction is titanic.

To avoid muscle fatigue secondary to this contraction the current

becomes surged

Effects on motor Effects on motor nervenerve

Effects of Muscle Contraction

Increased muscle metabolism. Increase oxygen demand by the muscles.

Increase output of waste product & metabolites (carbon dioxide, lactic acid).

Dilatation of capillaries and arterioles Increased blood flow

Increase local temperature. Increase venous and lymphatic drainage

Changes in muscle structure (fast twitch to slow twitch ) Increase joint range of motion.

Therapeutic Uses and Indication of Faradic Current Stimulation

Facilitation of Muscle Contraction & Re-education

Pain & muscle spasm, ◦ Quadriceps e.g. vastus medialis after knee injury & diseases

Prolonged disuse, wasting and imbalance◦ Intrinsic muscle of foot in case of longstanding flat foot.◦ Abductor hallucis in hallux valgus.◦ Scoliosis.◦ Prolonged period of immobilization

Muscle and nerve repair and transplantation.

Nerve injury (----What is the degrees of nerve injury?)

Pelvic floor Muscle (stress incontinence)

Improve Venous and Lymphatic drainage

Electrical stimulation of the muscle causes increase venous and lymphatic return, alter cell membrane permeability, these causes reduction of edema.

The treatment is most effective if the current is applied by the method, termed faradism under pressure

Faradism under pressure is stimulation of the muscle that generally act as the pump muscles and is combined with compression and elevation of the limb to increase venous and lymphatic drainage and hence relive edema.

Retardation of muscle atrophyMaintenance of muscle tissue after injury that prevent normal muscle

contraction can be achieved through using an electrical stimulated muscle contraction, which produce the physical and chemical events associated with normal voluntary muscle contraction and helps to maintain normal muscle function.

Increasing Range of Motion

Muscle contraction pulls the joint through limited range. The continued contraction of this muscle group over an extended time make the contracted joint and muscle tissues modify and lengthen

The person with foot drop is unable to

dorsiflex their foot.

The approximate electrode placements

for foot drop. The negative is placed over the peroneal

nerve.

The right quad has atrophied or wasted. Stimulation of the quad can prevent atrophy and increase strength.

Placement for quad weakness/atrophy.

APPLICATIONS

Post op ACLPost op ACL Problem: Quadriceps

atrophy Goal: Decrease

atrophy, increase strength.

Waveform: Symmetric Duty cycle: 25% (4:12) Placements:

Rotator cuff Rotator cuff repairrepair Problem: Rotator cuff

atrophy, poor scapular stability

Goal: Decrease/ reverse atrophy, scapular stabilizer re-ed.

Waveform: Symmetric/ asymmetric

Duty cycle: 25%, hand switch

Placements:

Isometric Abduction Scapular depression

Muscle re-education

Contraindication for Faradic Current Stimulation

Skin lesion & dermatological conditions such as eczema.

Infection such as osetomylities.

Vascular diseases such as thrombosis, & thrombophlebities.

Marked loss of skin sensation (chemical burn).

Unreliable patients.

Superficial metal (concentration of electricity).

Metal and cardiac pacemaker

Over recent or non-union fractures

Over potential malignancies

Treatment times & frequency

To be effective 2 & 3 treatments per week for the first 8-12 weeks

Treatments last 15-20 minutes but no longer than 30 minutes

It is better to have 3 short treatments per week than 1 long treatment