Neuromuscular Electrical Stimulation (NMES) Mohammed TA, Omar, Ph.D. PT Rehabilitation 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 for. Muscle re-education Prevention/Retardation of disuse atrophy Muscle strength and /or endurance Reduce edema (Muscle pump contraction)

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. The point where the motor nerve enters the muscle and it lies at muscles belly between the proximal one third & distal 2/3 of muscle belly or fleshy part of the muscle fibers. Motor point is the region in muscle where a great density of terminal motor end plates is found near the surface.

Position of the MP of quadriceps and gastrocnemii What is the Motor Point? To trace motor point Interrupted direct current at 1ms (1000µs) for innervated muscle Interrupted direct current at 100ms for denervated muscle Position of the muscle motor points for the quadriceps and gastrocnemii in 53 healthy subjects. The arrows indicate the average motor point (MP) positions along the respective reference lines. A) Vastus lateralis muscle MPs (blue circles, proximal MP; white circles, central MP; yellow circles, distal MP). The continuous black line is the reference line for the proximal MP, while the dashed black line is the reference line for the central and distal MPs. B) Rectus femoris muscle MPs (blue circles, proximal MP; yellow circles, distal MP). C) Vastus medialis muscle MPs (blue circles, proximal MP; yellow circles, distal MP). The continuous black line is the reference line for the proximal MP, while the dashed black line is the reference line for the distal MP. D) Medial (blue circles) and lateral (yellow circles) gastrocnemii muscle MPs. (Modified from Botter et al. [5]. Copyright © 2011 Springer. Used with permission provided by Copyright Clearance Center, license number: 2923641294715) 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

What is the Motor Unit? 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 neuron Motor neuron determines fiber type . Motor unit classification Muscle fiber classification Slow Type I slow oxidative (SO) Fast fatigue resistance Type II a fast oxidative glycolytic (FOG) Fast fatigue Type IIb fast glycolytic (FG)

What is the Motor Unit?

Sensory and motor nerve impulse propagation Orthodromic propagation is propagation of nerve impulse toward the sensory cortex. is a propagation of nerve impulse periphery toward neuromuscular junction Antidromic Propagation is propagation of nerve impulse toward the periphery (sensory receptors on the skin). is a propagation of nerve impulse proximally toward the CNS. When 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. Long pulse duration ≥ 10ms (comfortable stabbing sensation) Short pulse duration ≤ 1ms (mild/moderate prickling sensation). 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. 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 (SDC) 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. SDC test can be done 10 – 14 days after the lesion has occurred Take a neuromuscular stimulator uint having rectangular waveform with pulse duration i.e. 0.3, 0.1, 1, 3, 10, 30, 100, 300 ms and constant current. Put the active electrode over the fleshy belly of the muscle First apply current having longest duration and look for minimum perceptible contraction, Gradually shorten the impulse duration and note the corresponding increase in current strength. The electrode placement should not be changed through out the test. Plot a SD graph from the results of the te

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 The root word “rheo” means current and “base” means foundation: thus the rheobase is the foundation, or minimum, current (stimulus strength) that will produce a response. The root word “chrona” means time and “axie” means axis: chronaxie, then, is measured along the time axis and, thus, is a Duration that gives a response when the nerve is stimulated at twice the rheobase strength

Muscles that have loss nerve supply. 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 Loss of voluntary contraction and reflex activities 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 Paralysis (immediately): Fasiculation (immediately): spontaneous firing of the injured axon, causing twitching of motor units. Fibrillation (days) : spontaneous twitching of individual muscle fibers due changes in muscle excitability (e.g., Na channels) Muscle atrophy (>1 week): Receptiveness to innervation: allows reinnervation of the muscle by motor axons

Long Duration Interrupted Direct Current Unidirectional, interrupted direct current with following characteristic; Pulse duration Inter-Pulse Interval Frequency Long pulse duration (100ms-600ms) 100-300ms PD ≥ 300ms CD Depends on pulse duration e.g. If Pulse duration = 100ms Frequency of 30 Hz 3-5times of pulse duration. Waveforms shape: Saw-tooth, Triangular, & Trapezoid

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

triangular, trapezoidal Effects of LIDC Neuropraxia Compression on nerve 100ms, rectangular Axonotmesis partial denervation 100-600ms, triangular, trapezoidal Neurotmesis Complete denervation 100-2000ms 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 There are considerable literatures concerning the effects of electrics stimulation. In 1987 Spieloloz concluded that it will retard the muscle atrophy and degeneration but can not prevent it completely. In 1983 Devis provide evidences that all the denervated muscle fibers must be activated to produce isometric contractions. And isometric contractions are more effective than isotonic contractions and the regular contraction should commence (start or begin or cause to start) as soon as possible. In short value of electrical stimulation for denervated muscle is not proven and its application to gain muscle power what may be small benefits are obtain but not justified. If some of the motor units (motor end plate + motor nerve + muscle fibers) are intact galvanic current is the choice of treatment. Interrupted direct current is still recommended for the treatment of Axonotmesis and Neurotmesis nerve repair is to be taken.

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 duration A B

Faradic Current Stimulation Faradic current is a short-duration interrupted Surged direct current with a pulse duration of 0.1 to 1ms, and frequency of 30 -100Hz Frequency: Therapeutic frequency (0.5, 1.5, 10, 50, 75, 100 Hz)In order to achieve a constant contraction, the stimulus must be applied at rate of 30-60stimuli per seconds. Waveforms Rectangular shaped pulse more comfortable than triangular pulse for normal muscle contraction. If disuse atrophy triangular waveform can be used. Pulse duration (0.02-1ms) Therapeutic selection 0.02, 0.05, 0.1 & 1ms. PD=0.1ms , frequency of 70Hz, & Skin resistance = 50Ώ, PD=1ms with frequency of 50Hz, and skin resistance = 1000Ώ Polarity : Active electrodes usually the cathode (-) Faradic currents are always surged and interrupted for treatment purposes to produce a near-normal tetanic like muscles contraction and relaxation. Faradic current is surged so that the intensity of successive impulse increases gradually, each phase reaching a peak value greater than the preceding one, and than fail either gradually or suddenly (why). The current is surged at variable controlled speeds ranging from 4-30surged/minute with variable rest period. The surge can be modified to give surges of various duration, frequency and waveforms. Faradic current will not stimulate denerveated muscles, as the current required to stimulate dennervated muscles at 1ms, is usually too great to be tolerable by the patients..

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 Faradic currents will not stimulate denervated muscle: › The nerve supply to the muscle being treated must be intact because the intensity of current needed to depolarize the muscle membrane is too great to be comfortably tolerated by the patient in the absence of the nerve Effects on motor nerve

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) Indications: 1. Facilitation of muscle contraction inhibited by pain: Stimulation must be stopped when good voluntary contraction is obtained. 2. Muscle re-education: Muscle contraction is needed to restore the sense of movement in cases of prolonged disuse or incorrect use; and in muscle transplantation. The brain appreciates movement not muscle actions, so the current should be applied to cause the movement that the patient is unable to perform voluntarily. Training a new muscle action: After tendon transplantation, muscle may be required to perform a different action from that previously carried out. With stimulation by faradic current, the patient must concentrate with the new action and assist with voluntary contraction. Nerve damage: When a nerve is severed, degeneration of the axons takes place after several days. So, for a few days after the injury, the muscle contraction may be obtained with faradic current. It should be used to exercise the muscle as long as a good response is present but must be replaced by modified direct current as soon as the response begins to weaken. Improvement of venous and lymphatic drainage: › In oedema and gravitational ulcers, the venous and lymphatic return should be encouraged by the pumping action of the alternate muscle contraction and relaxation. Prevention and loosening of adhesions: › After effusion, adhesions are liable to form, which can be prevented by keeping structures moving with respect to each other. › Formed adhesions may be stretched and loosened by muscle contraction. Painful knee syndromes: › After trauma, there is inhibition of muscle contraction, leading to muscle atrophy.

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 atrophy Increasing Range of Motion Maintenance 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. APPLICATIONS The right quad has atrophied or wasted. Stimulation of the quad can prevent atrophy and increase strength. 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. Placement for quad weakness/atrophy.

Muscle re-education Post op ACL Rotator cuff repair Problem: Quadriceps atrophy Goal: Decrease atrophy, increase strength. Waveform: Symmetric Duty cycle: 25% (4:12) Placements: Rotator cuff repair 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

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