NMES
• Neuromuscular Electrical Stimulation (NMES) uses a device that sends
electrical impulses to nerves. This input causes muscles to contract
• The electrical stimulation can increase strength and range of motion, and
offset the effects of disuse
• It is often used to “re-train” or “re-educate” a muscle to function and to
build strength after a surgery or period of disuse.
• Generation of action potential in the circuit
Action potential travels down the neuron to the
motor end plate, where the sarco-plasmic
reticulum becomes depolarized , and ca is
released
Cross-bridge cycling between actin and myosin
filaments of the muscle results in overlapping of
sliding filaments , causing the muscle to shorten
(contract).
• Therapeutic NMES – Use of repetitive stimulation of activation of paralyzed
muscles to minimize specific impairments like limited ROM ,motor
weakness ,spasticity, cardiovascular de conditioning
• Functional NMES – Use of NMES to activate paralyzed muscle at a precised
sequence to assist in the performance of ADLs or to provide stability to a
joint or maintain biomechanical integrity and therefore function.
• Functional Electrical Stimulation or FES- FES involves the use of NMES to
activate muscles in a specific order and degree to complete a functional task.
Working of NMES
• An electric current is the directed flow of charged particles in some
conducting medium.
• Electric currents also occur naturally in human body, and for that there
are two conducting mediums : 1. ionic fluids 2. nerves
• Nerves are specialized , excitable tissues , designed to carry waves of
ion fluxes in the form of action potentials, action potentials carry the
impulses transmitted within the central and peripheral nervous system.
• Skeletal muscles are innervated by peripheral motor nerves organized
in a functional units known as Motor units
• The electrical current activates the motor units by inducing action
potentials in the motor nerve.
• Activation always takes place through the motor nerves because
the nerves are much more excitable . Intact motor nerve is a pre-
requisite for activating a muscle with NMES.
• Electrical waveforms used in NMES
1. Mono-phasic {one polarity only}
2. Biphasic {alternating polarity}
3. Pulsed {isolated pulses of current between which there is no current
flow}
4. Bursted {bursts of currents between which there is no current flow}
• Any of these waveforms can work well , but there are relative
advantages depending upon the application.
• Examples : Pulsed current , are especially useful for activating small
muscles.
• When there is a requirement of strong contractions of lower extremities
, biphasic waveforms will be more effective.
Stimulus parameters in nmes
• Pulse amplitude and duration control
• Both together regulates the charge of each pulse and so
determine the number of peripheral nerve fibers recruited with
each stimulus. •
• Amplitude control accompanies by balance control which
effectively shifts between the channels. As the balance control
is adjusted , the output amplitude on one channel rises while of
the other channel falls.
• optimal pulse duration likely lies between 50 and 1000
microseconds
• Frequency
• A train of electrically induced action potentials in rapid sucession will
result in corresponding series of twitches in targeted muscle.
• A frequency of 30-50 pulses per second produces a smooth tetanic
contraction.
INTENSITY
• Intensity in miliamperes varies with pulse duration.
• Short duration pulses require relatively higher intensities , where as
relatively low intensities are adequate with long-duration pulses.
• As intensity increases , force of contraction increases because more
motor units are recruited within motor nerve.
• Intensity should be tolerable for the subject as well as able to elicit
motor response.
Duty Cycle
• It is used to avoid fatigue.
• The off part allows ionic gradients and neurotransmitters to recover in
nerve and muscle.
• On : off ratio of 1:7 minimizes fatigue but its time consuming. And
ratio of 1:1 is rapid. So , 1:3 ratio is used clinically.
• 4 second of stimulation and 12 seconds of rest.
Ramping
• Ramp modulation controls are included in neuromuscular electrical
stimulation so that the pulse charge of phase of each stimulus may be
gradually increased or decreased.
• The gradual rise allows the gradual recruitment of nerve fiber and
comfortable initiation of contraction for subject.
• It is most effectively used in neurologically impaired patients.
• The gradual decline allows smooth movement.
Electrode size and placement
• If one of the electrode is smaller than other , the current density
will be greater under the electrode because the current pass
through a smaller area.
• Small electrodes are sometimes used to focus current over a
particular motor point, allowing isolated contraction in targeted
muscle.
• Larger electrodes are used for back region.
CONTRAINDICATION
• Unstable cardiac conditions
• Implanted pacemakers
• Acute danger or hemorrhage
• Acute danger of thromboembolism
Precautions
• Epilepsy
• Decreased sensation
• No stimulus over carotid sinus
• No stimulus across of through thorax
• No stimulus over larynx area
• Do not stimulate diseased skin
• Prosthetic joint motion restriction
• Avoid grounding faults
