NMES Flashcards
Define electrical stimulation NMES EMS FES TENS
Electrical stimulation is a means of producing contractions in
muscles by applying an electrical current via electrodes placed on the skin, thereby stimulating nerves and muscle fibres
NMES - Activation of muscle through intact peripheral nerve
EMS - Electrical muscle stimulation for direct activation of denervated muscle
FES - Use of NMES during a functional task (ankle dorsiflexion for foot clearance; cycling)
TENS – frequently used for analgesic purposes; does not elicit a
motor response
stimulation targets
TENS = sensory nerve receptors
NMES/ FES = intact peripheral nerve
FES - foot drops
EMS = direct muscle stimulation
increasing in intensity
motor unit
nerve depolarisation /excitation
motor point
Motor unit Motoneuron and the muscle fibres it innervates 7:1 eye muscle 1000:1 gastrocnemius Nerve depolarisation / excitation Resting potential reversed Na+ ions move into cells K+ ions out Motor point A site, usually on the surface of a muscle, where the amplitude of the stimulus required to fully activate the muscles is at a minimum
skeletal muscle fib
contraction speed
slow motor unit - slow
fast motor units - fast
contaction force
slow - low
fast hight
recruitment dominance
slow - recruited at low % of MVC <25%
fast - increasingly recruited at higher % of MVC or if plan to perform a fast movement
recruitment threshold low - easily activated 5-15 Hz firing freq. from MN fast - high - 30-50Hz - firing frquency from motor neuron
fatiguability - slow fatigue resistant
fast - fast fatiguing
role - control of normal functional postures and unloaded movements
fast - rapid or accelerated movement and high load activity
frequency
Each motor unit action potential is identical in amplitude and shape
Frequency varies
Human 5-50Hz
Stimulation threshold: pulse amplitude and pulse width needed for depolarisation of a cell membrane and propogation of an action potential, lower for nerve cells than muscle cells
NMES - clinical uses
Strengthening or maintaining muscle bulk
Facilitating voluntary muscle contraction
Gaining or maintaining range of motion
Reducing spasticity
As an orthotic substitute to produce functional movement
Cardiovascular effect
Shoulder subluxation
CNS vs NMES stimulatoin
CNS Recruits type I fibres first Asynchronous excitation of motor units Requires intact peripheral nerve Does not transform fibre types Achieves a slowly fatiguing contraction Requires intact CNS
Electrical Stimulation Recruits type II fibres first Synchronous excitation of motor units Can stimulate denervated muscle Can transform from type I to type II and vice versa Can rapidly fatigue a muscle Can bypass CNS
electrical stimulation parameters
channels
single / multi channel
current flow
unipolar
bipolar
electrodes
surface
percutaneous
implanted
trigger - switch
EMG
cyclical
Settings frequency pulse duration amplitude ramp up / ramp down
conditions amenable to NMES
Spinal cord injury Stroke Head injury Multiple sclerosis Cerebral Palsy
leg stimulation
Odstock foot stimulator
Bioness foot drop device
Walk aid
Knee-hab
Neurotech Vital
leg stimulation evidence stroke
‘Functional electrical stimulation should be used for foot-drop of central neurological origin provided normal arrangements are in place for clinical governance, consent and audit’
‘Therapeutic electrical stimulation for treatment of the lower limb following stroke should only be used in the context of a clinical trial’
Goals of NMES in SCI
To reverse some of the dramatic losses in skeletal muscle mass
To stimulate functional improvements in people with incomplete
paralysis
To produce some of the health benefits associated with exercise
spinal cord injury
‘FES-assisted exercise is beneficial in preventing and restoring lower limb muscle atrophy as well as improving lower limb muscle strength and endurance in motor complete SCI’
FES cycling → 10-12% hypertrophy of quads
FES may be helpful in ameliorating negative effects of deconditioning (Ho et al, 2014)
Froztler et al (2008): high volume training (60 minute sessions 5 days a week for a year) → 35% hypertrophy
May increase strength in partially paralysed muscles, but quality of evidence of low (Ribeiro de Freitas et al, 2018)
(Muscle atrophy from UMNL tends to affect type II muscle fibres predominantly)
arm stimulation evidence stroke
‘Consider people for functional electrical stimulation of the supraspinatus and deltoid muscles if they have developed, or are developing, shoulder subluxation’
No other recommendations for the upper limb
stroke
‘Do not routinely offer people with stroke electrical stimulation for their hand and arm’
‘Consider a trial of electrical stimulation in people who have evidence of muscle contraction after stroke but cannot move their arm against resistance’
‘Continue electrical stimulation if progress towards clear functional goals has been demonstrated (for example, maintaining range of movement, or improving grasp and release)’
