NMES

Question 1

NMES - what is it

Answer 1

Form of electrical stimulation at sufficiently high intensities to produce muscular contraction

Healthy muscle
Injured/weakened muscle
Neurological conditions e.g. stroke, peripheral nerve lesions, spinal cord injury, cerebral palsy

Innervated muscle- via motor nerve
Denervated muscle- muscle directly

Question 2

The motor unit

Answer 2

Consists of:
the anterior horn cell

The motor nerve emanating from it

the individual muscle fibres it supplies

Question 3

muscle fibre types
Type 1
Type 2

Answer 3

Type 1
Slow twitch 
Red, highly vascular
Predominate in postural
muscles
Small diameter motor neurones
Low conduction velocity
Frequency rate 20-30hz
Many oxidative enzymes , hence fatigue slowly

Type 2
Fast twitch
Glycolitic
White, less vascular
Higher conduction velocities
Large force for short periods
Frequency rate of 50-150 Hz

Question 4

voluntary muscle contraction

Answer 4

All muscles contain a mixture of both types
Type 1 fibres recruited first
Followed by Type II
Asynchronous firing of motor neurons (smoother contraction)
Force of contraction is graded by
Spatial summation
Temporal summation
As more units become involved, muscle force is increased by increased rates of nerve firing

Question 5

electrical stimulation of innervated muscles

Answer 5

Synchronous firing of all motor units that are stimulated (jerky contraction)
Different recruitment order to voluntary contraction
Type II are more easily stimulated
Need longer rest times
Also stimulate sensory nerves
Frequency is fixed
Change the amplitude to increase strength of contraction
Structural changes occur in muscle with long term stimulation

Question 6

long term effects of NMES

Answer 6

Neural Plasticity
Neural activation 
5-6 weeks 
Muscle Plasticity 
Change in fibre type is response to frequency of stimulation
Conversion from Type II to Type I fibres
Conversion from Type I to Type II fibres (more complex, less literature)
Slower changes (months)
Vascular Changes

Question 7

Nerve stimulation

Answer 7

Sensory
Fibre type? A beta
Frequency/Fibre type?

Pain
Fibre type?
Frequency/Fibre type?

Question 8

theories of strength using NMES

Answer 8

Overload principle
greater strength gains occur at higher contraction intensities.

Preferential Stimulation of Type II fibres
develop more force.

Use MVIC as a criterion measure

Question 9

Uses of NMES

Answer 9

Strengthen normal muscle ?
Muscle inhibition secondary to pain and swelling
Post surgery 
Post immobilisation 
Post injury e.g. soft tissue/#
Nervous System Problem- CNS/PNS
General muscle atrophy/weakness
Why? 
Increase muscle strength and endurance 
Change muscle structure and function

Question 10

Normal muscle

Answer 10

Can ES lead to an increase in muscle strength?
Is it more effective than voluntary exercise?

Studies by Currier and Mann (1983) and Wolf et al (1986) demonstrated that combined NMES and exercise was no more effective than exercise alone

Bircan et al (2003), Pfeifer et al (1997), Fitzgerald et al (2003) found combined NMES and exercise more effective than exercise alone. Strength gains of up to 25% in some cases

Question 11

weakened muscle

Answer 11

Can be useful in atrophied muscle

Following immobilisation or contraindications to dynamic exercise
Post surgery/injury 
Following removal of Cast post fracture 
Pelvic Floor dysfunction
Nerve injury

Question 12

pelvic floor strenghthening

Answer 12

Urinary incontinence

Can use special vaginal electrodes

However, exercise should be the first treatment option (Bo, 1998)

Question 13

electrical stimulation in neurological conditions

Answer 13

Improve motor function
Increasing muscle strength
Reducing spasticity
Stroke 
Some evidence (Glinsky et al, 2007)
Reducing shoulder subluxation in stroke
Stimulate posterior deltoid and supraspinatus (Ada and Foongchomcheay, 2002)
Improvement in wrist extensor and grip strength (Rosewilliam et al, 2012)
Functional Electrical Stimulation

Question 14

Functional electrical stimulation FES

Answer 14

To enable a muscle to contract to enhance or produce functional movement
e.g enhance dorsiflexion during gait in neurological conditions such as stroke, cerebral palsy

Question 15

denervated muscle

Answer 15

Results in
Atrophy
Fibrosis
Degeneration and fibrosis of the motor nerves
Increased fatty tissue
Thickening of arterial walls
In general little damage in first 3 months
Changes become more marked after 1 year
If repair occurs after 3 years denervation, muscle is unlikely to ever functionally recover

Question 16

electrical stimulation in denervated muscle

Answer 16

Main purpose: to prevent or slow atrophy whilst waiting for re-innervation
Debatable and controversial
May inhibit the regrowth of nerves (axonal sprouting).
Literature contradictory (Brown and Holland, 1979; Politis et al, 1988, Pockett and Gavin, 1985)
? Impractical due to costs and compliance
Muscle fibres can be stimulated directly
Requires different type of current: interrupted direct current
As muscle is less excitable than nerve, more charge is required i.e. higher intensities and longer pulse durations. (30 msec+)
Contractions are slower, worm like.
Slow rising pulses can stimulate muscle directly as it has less ability to adapt than nerve.
No consensus on parameters

Question 17

types of NMES currents

Answer 17

Symmetrical Biphasic Pulsed Current most commonly used
(similar current type as used in TENS)

Others
Faradic Currents
Interferential Current

Question 18

treatment parameters for innervated muscle

Answer 18

Frequency

Pulse Duration

Amplitude (Intensity)

On: Off time

Ramp up/down

Question 19

which frequency

Answer 19

Stimulation at low frequencies (20-30Hz) for sustained periods best for slow twitch fibres

Less likely to transform to fast-twitch fibres

Stimulation at high frequencies (30-50Hz) for brief periods best for fast twitch fibres

Used to increase muscle strength

Question 20

on off times

Answer 20

Synonymous with contraction duration and rest interval

Rest interval is required to replenish ATP and CP.

Depends on the condition

Longer off time for strengthening –Type II fibres

Question 21

Ramp

Answer 21

Ramp up and down

Influenced by the on:off time and the intensity of the current

Should not be too long- avoid prolonged tingling before contraction force reaches target levels

Most studies have used ramps of 5 seconds without any specific rationale

Question 22

current amplitude/intensity

Answer 22

Intensity need to be sufficient enough to generate contraction

Higher for strengthening than endurance

50% of MVIC

However, the sensory sensation may be uncomfortable and may impede ability to tolerate

The amplitude should be increased as often and as much as tolerated during treatment session
However, there are upper limits of patient tolerance and fatigue

Question 23

parameters for strength vs endurance

KNOW

Answer 23

frequency s: 50-80hz
E: 1-30Hz

Pulse duration
s: 100-600 microseconds
E: 100-600 microseconds

on: off time
S:Ratio of 1:5 or 1:3 with on time of 5 secs
E: ratio of 1:1 or 1:2 with on time of 8 seconds +

Ramp s:2 sec
E: 2 sec

treatment time S: 10-20 mins
E: 20 mins –> hours

Intensity: S:high E:moderate

Question 24

fatigue

Answer 24

Fatigue can be a problem especially is applying NMES for few hours a day

Can be limited by
Increasing on: off ratio
Reducing the pulse duration
Start with short treatment times

Question 25

parameters for electrical stimulation of denervated muscle

Answer 25

Slow rising pulses: 50 to 100ms ramp time Pulse Durations of 100, 300, 500 ms. Frequency: 1/2 seconds i.e. 30/minute High intensities

Question 26

electrode size

Answer 26

Depends on the target muscle Small muscles tend to lead to stronger muscle contractions The larger the electrode, the lower the intensity per unit area. If too large, may not get contraction of intended muscle

Question 27

electrode placement

Answer 27

Unipolar Technique One electrode over the ‘motor point’. Point where the muscle can contract with the least energy - easier to stimulate In general, this is over the muscle belly, at the junction of the upper and middle thirds, but not always Other electrode is ‘indifferent’, convenient to the muscle being treated

Question 28

bipolar technique

Answer 28

Bipolar technique Electrodes of similar size are placed at either end of a muscle belly Less precise than unipolar where motor point has been identified

Question 29

to locate motor point

Answer 29

2 electrodes Reference electrode (stationary) Moving electrode (over the motor point) Aim to find the best location where you get the strongest contraction. This is where you will place the electrode for treatment Do not need to set ramps, contract/relax time Will only be using for short period Use constant voltage for patient comfort Put reference electrode on (distal muscle belly) Turn on IFT, Set Parameters: Carrier Frequency = 2000Hz Frequency = 30 Hz (no sweep) 2 pole Constant Voltage – select CV Set time Apply active electrode to imagined motor point (at the junction of the upper and middle thirds) Turn on Intensity and gradually increase Try a few different points to identify the motor point Point of best contraction = motor point

Question 30

To stimulate muscle for treatment

Answer 30

Can use a variety of machines e.g. IFT Smaller more convenient machines now with better options e.g. Neurotech 2000/ Neurotrac Unipolar Technique- if you have found motor point Bipolar Technique- if you have NOT located motor point Ref Parameters

Question 31

sharp blunt test

Answer 31

Must be done prior to first treatment Use specialised instrument with a sharp end and a blunt end Explain test to patient and demonstrate on an area separate to area being tested Ask patient to close eyes Apply sharp and blunt ends to the area to be tested, randomly If patient cannot tell difference between sharp & blunt  sensation impaired: NMSE not appropriate

Question 32

principles of application

Answer 32

``` Check contra-indications Check skin sensation- blunt/ sharp Remove jewellery/clothing etc Prepare skin Switch machine on Set parameters within machine Self-test Position electrodes securely on patient’s skin Connect lead to machine Gradually turn up intensity until patient feels strong contraction ```

Question 33

contra-indications

Answer 33

``` Pacemaker PVD Hyper/hypotensive Neoplasm Active infection Deep X-ray Therapy Comprehension Carotid sinuses Over thoracic region Over Pregnant uterus ```

Question 34

NMES application

Answer 34

Introduction to patient and Explanation of procedure Check contra-indications Remove jewelry/clothing etc Check blunt/sharp skin sensation Ensure area to be treated is fully supported. For best contraction –position muscle in mid-range Switch machine on /Set parameters –ensure amplitude at 0 This may vary by machine. For some you can set parameters with machine off and others have to be set with machine on Position electrodes securely on patient’s skin Connect electrodes to the machine leads Advise patient that you are going to turn up amplitude and they should feel a ‘strong, sensation and muscle contraction’ Gradually turn up intensity. Turn up only in the ‘On’ phase to avoid a sudden increase in intensity

Question 35

termination of treatment

Answer 35

``` Slowly decrease intensity Switch machine off Disconnect electrodes from lead Remove electrodes from patient’s skin Check patient’s skin Reassess any relevant outcomes Record treatment ```

Question 36

Hazards

Answer 36

Chemical burn (especially if using DC or Interrupted DC) Interference by SWT Caution when turning up intensity- avoid turning up during off phase. Otherwise patient could experience a sudden sensation/contraction

Question 37

post surgery

Answer 37

Total Knee Replacement Cochrane review (Monaghon et al, 2010) 2 RCTs Inconclusive evidence for NMES ACL Repair: Systematic review (Hauger et al, 2018) 11 RCTs NMES in addition to standard physical therapy appears to significantly improve quadriceps strength and physical function in the early post-operative period compared to standard physical therapy alone.

Question 38

NMES summary

Answer 38

NMES-electrical stimulation at sufficiently high intensities to produce muscular contraction Form of electrical current- safety, precaution and contra-indications considerations. Consider strength and endurance components Applications for weakened muscle> healthy muscle Research indicates it is an adjunctive therapy to traditional strengthening exercise