4 Electrical Currents for Muscle Contraction

what is NMES? what does it stimulate? what are the goals when using NMES?

neuromuscular electrical stimulation

innervated muscle

intact peripheral nerve depolarized first to initiate skeletal muscle contraction

goal is strength, reeducation, etc

what is FES? what does it stimulate? what are the goals when using FES?

functional electrical stimulation

innervated and denervated muscle

goal is to facilitate or enhance functional movement

what is EMS? what does it stimulate? what are the goals when using EMS?

electrical muscle stimulation

denervated muscle

depolarizes the muscle itself

goal is to preserve muscle while nerve regenerates (is controversial)

what are the indications for NMES?

requires intact and functioning PNS

strengthens muscle

enhance muscle recruitment

facilitation of weak, inhibited muscles

slow down or prevent muscle atrophy

decrease spasticity

control edema

restore function

what is the goal of NMES according to Maffiuletti et al?

maintaining/preserving neuromuscular function during disuse

restoring neuromuscular function after disuse

improving neuromuscular function in able-bodied individuals

how is an action potential propagated?

the nerves become depolarized and then nerve fibers innervated by them contract

what occurs in a physiologic muscle contraction?

smaller type I fibers are activated before larger muscle fibers and produce lower-force contractions that are fatigue and atrophy resistant

contract has a smooth onset due to synchronous recruitment of motor units

what occurs in an NMES muscle contraction?

large diameter type II fibers are activated first before smaller fibers

produce strongest and quickest contractions

fatigue rapidly and atrophy rapidly with disuse

muscle contraction is rapid and jerky at onset

T/F NMES is very effective at strengthening fibers that are weak secondary to disuse.

T

how do you maximize strength gains with NMES?

patient should perform physiologic contractions with NMES

T/F rest times should not be provided between NMES contractions.

F

how to get muscle strengthening?

increase muscle fiber size

improve motor unit recruitment (nonmotor mass adaptation) which occurs through number of MU recruited, frequency of MU recruited, and recruitment in a synchronized manner

what are the 2 mechanisms that strengthening occurs through that could be used as a guideline for NMES?

1. overload principle

2. specificity theory

what is the overload principle? how does it relate to NMES?

greater load placed on muscle and greater force of the contraction produced results in more strength gained

externally applied resistance

force increased by increasing the total amount of current in NMES (more pulse duration, amplitude, electrode size)

what is the specificity theory? how does it relate to NMES?

muscle contractions specifically strengthen muscle fibers that contract

NMES has more effect on type II fibers

evidence indicates that with type II fiber atrophy, early use of NMES increases strength gains

NMES for strength vs endurance

strength: greater-force contractions used by adjusting pulse duration and amplitude

endurance: prolonged stimulation with lower-force contractions used

NMES application in ACL injury and repair

NMES can accelerate recovery where immobilization and rest lead to type II fiber atrophy

greater strength gains with NMES than with exercise alone

strongest NMES effects found when applied after first week post-op

NMES and voluntary contractions are equally effective when performed at the same intensities

with aging, what happens to type I and II fibers?

decreased number of type I and II fibers, decreased size of type II fibers

NMES clinical application in OA and TKA

NMES used early along with voluntary exercise can help attenuate quad and HS strength losses

NMES is helpful adjunct to strengthening because it doesn’t affect pain in patients with OA

NMES clinical application in critical illness

individuals may not be able to participate in resistance exercise or mobility training

helps patients in ICU who experience significant declines in function, muscle weakness and fatigue

NMES preserves muscle strength and mass, reduces rate of muscle degradation

in COPD, increase type I fibers, quad force and 6MWT

NMES clinical application in CNS damage

NMES can activate peripheral nerves for muscle contraction

improves muscle control

sensory input can cue initiating movement or activate muscle group

can integrate use into functional activities (FES) - stimulates contraction when muscle should contract

may reduce spasticity

EMS for denervated muscle

controversial

can aid in preserving muscles when reinnervation is anticipated

if used, start early and use on superficial muscles

T/F with NMES, the earlier the better

T

if ______ is the same, NMES training and volitional muscle contractions show the same benefits

intensity

in ____ patients, no added benefit of NMES and exercise over either alone

healthy

weakened muscles may be best strengthened ______ with NMES.

initially; once pt can produce greater voluntary contraction, transition to exercise

what are contraindications for NMES?

cardiac pacemaker/electronic implants

unstable arrhythmias

malignant tumors

over carotid sinus/ant neck/head/reproductive organs/chest

active DVT or thrombophlebitis

in area of hemorrhage or active infection

over damaged skin; recently radiated skin

pregnancy

recent fx, surgery, osteopenia

lower abdomen

sometimes poor circulation included in contraindications

what are precautions for NMES

impaired sensation

impaired circulation

impaired mentation

skin disease/irritation

neuropathies/irritation

active epiphysis

cardiac disease

waveform types

biphasic pulsed: symmetrical, asymmetrical

russian (burst modulated AC)

when to use symmetrical vs asymmetrical biphasic pulsed current

symmetrical: comfort for larger muscles

asymmetrical: comfort for smaller muscles

asymmetrical may be more effective overall

what is a russian waveform

burst-modulated AC

continuous wave of AC broken into bursts of many cycles grouped together

what is a good starting point for pulse duration?

350-450 µsec

use highest tolerated for most effectiveness

what is the purpose of adjusting frequency?

goal is to have a smooth, forceful contraction

higher the frequency, more fatigue - 30-50 pps most common, increase to >50 pps for hypertrophy, 50-75 pps for large muscle groups

what should the amplitude be for NMES?

max tolerated; goal is a strong tetanic contraction

start at around 30% then ≥50% of MVC

what is ramp time? how long should it be?

gives patient a heads up for comfort

longer ramp = less total activation time

1-4 sec/1-2 sec down

what is duty cycle?

on/off time ratio

consider inhibition, endurance, hypertrophy

time/duration of NMES

at least 10 contractions, 10 seconds most common

wide variation in treatment protocols and the literature

what is russian protocol?

medium frequency: 2500 Hz, 50 bursts/sec

duty cycle (within burst): 50% (bursts last 10 ms with 10ms interburst interval)

cycle (on:off) time: 10 sec on, 50 sec off, ramp 2-3 sec

total tx time: 10 min duration (10 cycles)

intensity: max tolerable

how to apply electrode? what are the configuration types?

match electrode to target muscle size, apply 1st pad to motor point and 2nd pad parallel to fiber direction

monopolar, bipolar, quadripolar

monitoring NMES treatment

PT should see visible contraction

modify joint angles to optimize recruitment

education patient on DOMS

cue patient to assist/not assist

skin check

document electrode placement

(10% of population may not tolerate NMES)