NMES Flashcards
NMES - what is it
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
The motor unit
Consists of:
the anterior horn cell
The motor nerve emanating from it
the individual muscle fibres it supplies
muscle fibre types
Type 1
Type 2
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
voluntary muscle contraction
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
electrical stimulation of innervated muscles
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
long term effects of NMES
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
Nerve stimulation
Sensory
Fibre type? A beta
Frequency/Fibre type?
Pain
Fibre type?
Frequency/Fibre type?
theories of strength using NMES
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
Uses of NMES
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
Normal muscle
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
weakened muscle
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
pelvic floor strenghthening
Urinary incontinence
Can use special vaginal electrodes
However, exercise should be the first treatment option (Bo, 1998)
electrical stimulation in neurological conditions
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
Functional electrical stimulation FES
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
denervated muscle
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
electrical stimulation in denervated muscle
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
types of NMES currents
Symmetrical Biphasic Pulsed Current most commonly used
(similar current type as used in TENS)
Others
Faradic Currents
Interferential Current
treatment parameters for innervated muscle
Frequency
Pulse Duration
Amplitude (Intensity)
On: Off time
Ramp up/down
which frequency
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
on off times
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
Ramp
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
current amplitude/intensity
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
parameters for strength vs endurance
KNOW
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
fatigue
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
parameters for electrical stimulation of denervated muscle
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
electrode size
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
electrode placement
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
bipolar technique
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
to locate motor point
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
To stimulate muscle for treatment
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
sharp blunt test
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
principles of application
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
contra-indications
Pacemaker PVD Hyper/hypotensive Neoplasm Active infection Deep X-ray Therapy Comprehension Carotid sinuses Over thoracic region Over Pregnant uterus
NMES application
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
termination of treatment
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
Hazards
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
post surgery
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.
NMES summary
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
