Electrical Currents and NMES

when targeting muscle strengthening with NMES: - what pulse frequency is used for small muscles and for larger muscles? - what pulse duration is used for small/large? - amplitude? - on:off times? - ramp time? - treatment time? - times per day?

- 35-50 pps (lower for small, higher for large) - 150-200 microseconds for small; 200-350 for large - >10% MVC injured muscle; >50% MVC uninjured - 1:5 working down to 1:3 over sessions - at least 2 seconds - 10-20 minutes (or 10-20 contractions) - 2-3 hours when awake

what are the 2 differences in physiology of muscle contractions between NMES and physiological contractions?

- order of recruitment of motor units (NMES = largest units first; physiological = smallest units first) - smoothness of onset of contraction (NMES = jerky, rapid because all motor units of a given size fire simultaneously; physiological = gradual, smooth because force is regulated by recruitment of smaller motor units, building up)

What are 3 major areas for clinical application of NMES?

- orthopedic conditions (post surgery) - neurological conditions (stroke, cerebral palsy, etc.) - sports medicine (strength training)

What are the 2 mechanisms for muscle strengthening used by NMES?

- overload principle - specificity principle

for muscle re-education (FES), what parameters are used on NMES?

-35-50pps (lower for small, higher for large) - 150-200 microseconds (for small) 200-350 (for large) - amplitude sufficient for functional activity - on:off dependent on activity - ramp of at least 2s - treatment time depends on activity

for muscle spasm reduction, which parameters are used on NMES?

-35-50pps (lower for small, higher for large) - 150-200 microseconds (for small) 200-350 (for large) - amplitude to visible contraction - on:off (1:1 ratio, between 2-5 seconds each) - ramp time at least 1 second - treatment 10-30 minutes - every 2-3 hours until spasm is gone

for edema reduction using muscle pump, which parameters to use with NMES?

-35-50pps (lower for small, higher for large) - 150-200 microseconds (for small) 200-350 (for large) - amplitude to visible contraction - on:off (1:1 ratio, between 2-5 seconds each) - ramp time at least 1 second - treatment 30 minutes - twice a day

to produce strength gains in injured muscle, the force of the stimulation needs to be greater than or equal to _____% of maximal voluntary contraction

10%

type ____ fibers respond the best to NMES

2

to produce strength gains in healthy muscle, the force of the stimulation needs to be at least _____% of maximal voluntary contraction

50%

what is the Russian protocol?

AC set to 2500 Hz, delivered in 50 burst/second (each burst is 10us long and separated by 10us interval)

what are the 3 types of electrical currents?

DC, AC, PC

what type of NMES is used for strength improvement of people with neurological conditions ?

FES (functional electrical stimulation)

what is chronaxie?

Minimum amount of time it takes to cause a contraction at 2x rheobase

what is the strength duration curve?

a graphic representation of the minimum combination of amplitude and pulse duration needed to depolarize a nerve

what are the ionic effects in the tissue of DC, pulsed monophasic, and unbalanced biphasic currents?

a net ionic effect (tissue stays charged)

what is the specific NMES protocol?

a pulsed biphasic waveform or russian protocol

what is accommodation?

a transient increase in threshold to nerve excitation (nerve gradually becomes less responsive to stimulation)

modulation is used to limit ______

accommodation

what is AC?

alternating current - continuous bidirectional charged particles

what is modulation?

any pattern or variation in one or more of stimulation parameters

what is Functional electrical stimulation?

application of electrical current to produce muscle contraction during functional activity (e.g., dorsiflexion while walking)

EMS is used primarily to delay _____ and _____ of denervated muscles

atrophy fibrosis

What is a monophasic current?

current flowing in one direction (DC)

what is biphasic current?

current flowing in one direction, then in the opposite direction (AC)

what is DC current?

direct current - a continuous unidirectional flow of charged particles

what is phase duration?

duration of one phase of the pulse (microseconds)

what is electrical muscle stimulation?

electrical current stimulates denervated muscle fibers

what is EMS and when is it used?

electrical muscle stimulation - used to initiate muscle contraction in denervated muscles (peripheral motor nerve not functioning)

what is the specificity principle?

electrical stimulation specifically strengthens the muscle fibers that contract

AC has ____ ion flow in each direction, therefore no charge remains in tissue

equal

amplitude can effect how the stimulation ______ and what types of _____ are activated by the current

feels nerves

motor nerves have a ______ amplitude and ______ pulse duration

higher longer

for EMS, what parameters are important in allowing for muscle fibers to depolarize?

long pulse duration (at least 10 milliseconds)

sensory nerves have a ____ amplitude and a ______ pulse duration

lower short

what is amplitude?

magnitude of current (intensity/strength of current)

motor points are over the _____ of the muscle belly

middle

what is a rheobase?

minimum amplitude required with a long pulse duration to produce an AP

what are 2 types of pulsed current (PC)?

monophasic biphasic

what are electrical currents?

movement or flow of charged particles (electrons and ions) through a conductor in response to an applied electrical field

what is neuromuscular electrical stimulation?

muscles contract in response to electrical stimulation when AP in motor nerve reaches the muscle

what are the ionic effect in the tissue of AC and balanced biphasic currents?

no ionic effect (tissue does not stay charged)

where do you place electrodes for NMES?

one over the motor point and the other over the muscle belly (both electrodes aligned parallel with muscle fibers)

AC is generally used for:

pain control and muscle contractions in innervated muscles

to use NMES, patient must have intact and functioning _____ _____ _____

peripheral nervous system

muscle contractions produced by NMES are not the same as ______ contractions

physiological

to improve endurance with NMES, stimulate ________ contractions with ______ force

prolonged lower

What is PC?

pulsed current - interrupted flow of charged particles whereby the current flows in a series of pulses separated by periods when no current flows

what is the overload principle?

the greater the load placed on a muscle and the higher force contraction it produces, the more strength that muscle will gain

what is the motor point of a muscle?

the place where an electrical stimulus will produce the greatest contraction with the least amount of electricity

what is an interpulse interval?

time between pulses

what is pulse duration?

time from the beginning of the first phase of a pulse to the end of the last phase of a pulse (microseconds)

DC is generally used for:

tissue healing, iontophoresis, muscle contractions in denervated muscles

with EMS, studies have shown that as soon as you stop treatment, effects slowly wean off (t/f)

true

DC has an _____ pulse charge, meaning that the pulse charge remains in the tissue

unequal