Neuromuscular Electrical Stimulation (NEMS)/Biofeedback (WEEK 11) Flashcards
What is NMES? Goal?
Electrical current that is delivered to the surface of the skin.
Goal: produce muscle contractions through the stimulation of motor nerves
- retrain inhibited muscles
- strengthen weakened muscles
- oedema control
How does NMES work (4 steps)
- Application of sufficient electrical current will depolarize the motor neurons
- The signal propagates to the NM junction
- NT ACh is released by the nerve into the NMJ and binds to the receptor site at the muscle
- The muscle fiber fires
What structure contains ACh?
Axon terminal has vesicles that contains ACh
ACh receptor site?
Muscle
Treatment Parameters: Intensity
As intensity increases, the number of stimulated MU is increased, resulting in an increase in force generation
Treatment parameters: Pulse duration
Recommended:
> 250usec
Treatment parameters: Frequency
- low frequency
- ideal/therapeutic frequency
- low frequency (<20Hz): the muscle twitches
- 30-50Hz: titanic contraction (Sustained); just looking for a constant contraction
Frequency recommendation:
Lowest frequency needed to get a sustain contraction - replicate functional activity
Treatment parameters: increasing frequency and the problem with increasing frequency
- force contraction increases with frequency (increased muscle force production)
at high frequency we will get constant contraction of the muscle, we are potentially depleting all the NT not because of meaningful training, rather we are running out of NT
- high frequency brings on fatigue more rapidly which may not be desirable
- Fatigue due NT depletion which has no therapeutic benefit to patient
Treatment parameters: Time
- helps to replicate a normal physiological contraction and/or replicate functional movements
Time parameters:
- On time
- Off time
- Rise time
- Fall time
- On: Determines the duration of muscle contraction (may or may not include rise/fall time)
Time Parameters: Off time
- On: Determines the duration of muscle contraction (may or may not include rise/fall time)
- Off: Rest time between contractions
- Ramp (rise): gradual increase in intensity until the desired intensity is reached; avoids the discomfort of a sudden strong contraction
- Fall: gradual decrease in intensity at the end of contraction
Time parameters: Rise (Ramp) Time
- On: Determines the duration of muscle contraction (may or may not include rise/fall time)
- Off: Rest time between contractions
- Ramp (rise): gradual increase in intensity until the desired intensity is reached; avoids the discomfort of a sudden strong contraction
- Fall: gradual decrease in intensity at the end of contraction
Time parameters: Fall time
- On: Determines the duration of muscle contraction (may or may not include rise/fall time)
- Off: Rest time between contractions
- Ramp (rise): gradual increase in intensity until the desired intensity is reached; avoids the discomfort of a sudden strong contraction
- Fall: gradual decrease in intensity at the end of contraction
Common clinical use of NMES
- overdose muscle inhibition post-injury or post-surgery
- Strengthen muscles post -injury, -surgery, or to combat deconditioning
- Control oedema in immobilized limbs (via muscle pumps)
Limitations in clinical use of NMES
- electrically stimulated muscles do not produce a normal physiological contraction
- fatigue is an issue
- hard to produce a contraction greater than 20-30% of MVC without sassing too much discomfort; there is a limit to the amount of stimulation that can be applied. (E.g. higher intensity stimulates nocicpetive nerves along with motor nerves - pain threshold)
Physiological vs. NMES contraction: recruitment of fast and slow twitch fires
Physiological: slow twitch are recruited first, fast twitch excited with increased force
NMES: non-selective recruitment of fast- and slow- twitch fibers (can’t go from slow —> fast)
Physiological vs. NMES: inhibition of alpha-motor neuron
Physiological: strong stimulation of GTO will cause inhibition, preventing excessively strong contraction
NMES: GTO is stimulated but inhibition is prevented due to direct electively stimulation of the motor nerve
Physiological vs. NMES contraction: Synchrony of firing
Physiological: smooth (only what is needed is recruited)
NMES: jerky (all or none) effect
Physiological vs. NMES: fatigue
Physiological: minimal fatigue (only certain fibers fires, when tired others take over creating a smooth contraction)
NMES: any fibers in path will be stimulated therefore onset of fatigue is fast
Muscle fiber recruitment via electrical stimulation
Electrical stims recruit muscle fibers in reverse order of a normal contraction
- fast is recruited before slow due to larger axon size of fast twitch MU
- only true when muscles stimulated with electric current
- NMES non-selective of what fiber type is stimulated (simply stimulates what is in range)
Physiological vs. NMES: stimulation of alpha motor neuron and effect on GTO inhibition
how does this relate to pain
Physiological: GTO inhibits AMN from excessive contraction
NMES: No GTO inhibition because AMN stimulated in periphery instead of dorsal root horn
-stimulation of alpha motor neuron in periphery prevents GTO inhibition
- may be related to 20-30%MVC; limited due to pain of contraction
Physiological muscle fiber stimulation
- muscle made up of many MU
- during sustained physiological contraction, different MU will fire asynchronously with different MU turning on/off at different times, resulting in a smooth muscle contraction and also delays the onset of fatigue
Parameters: Strengthen weak muscles
Goal?
- Produce strong muscle contraction
- augment voluntary contraction by the patient
Parameters: Strengthen weak muscles
Parameters:
- Pulse duration
- Pulse rate
- On time
- Off time
- Ramp time
- Current intensity
- Time/reps
- PD >250usec
- PR 50-80Hz
- On 10s
- Off 3-4x the on time
- Ramp 2-5sec
- Current intensity high (produce ms contraction)
- Time/reps: vary. Lower number of reps is generally suggested since the goal is to increase strength
Parameters: Retrain inhibited muscle
Goal?
Low grade contraction to facilitate the feel of a voluntary contraction. Pt instructed to contract the muscle along with the electrical stimulation as part of the retaining process
Parameters: Retained inhibited
Parameters:
- Pulse duration
- Pulse rate
- On time
- Off time
- Ramp time
- Current intensity
- Rime/reps
PD > 250usec
PR 50 Hz
On 2-3sec
Off 3-4x the on time
Ramp Long (2-5)
Current Intensity just enough to produce contraction
Time/reps: depends on therapeutic goals (e.g. 30 reps or to fatigue)
Parameters: Edema control via muscle pump
Goal?
Low grade contraction to facilitate muscle pump but I minimize fatigue
Parameters: Edema Control via muscle pump
Parameters:
- Pulse duration
- Pulse rate
- On time
- Off time
- Ramp time
- Current intensity
- Rime/reps
- PD > 250usec
- PR 30-50Hz
- On 5-10s
- Off 1:1 ratio ON time
- Ramp time short 2-3 secs
- Current intensity: just enough to produce a contraction
- time/reps: 30 mins, several time per week
NMES: ACL repair
Goal & Effect
Goal:
- combat disuse atrophy of the quadriceps, often focusing on VMO activation
Effect:
- NMES combined with exercise may be more effective in improving quadriceps strength than exercise alone
NMES: TKA
- Used as an adjunct treatment to standard rehab and had significantly great improvements in strength, functional performance, and knee extension ROM (at 3.5 weeks and 1 year follow up)
NMES: quad strengthening (unimpaired)
- no better than exercise, but volitional exercise is better than NMES
NMES: quadriceps strengthening (impaired quads)
Post-surgery/injury: NMES not better than volitional exercise
In-cast or immobilization patients: NMES better than no exercise and volitional in-cast exercise
NMES: quadriceps strengthening for adults with advanced disease (COPD, chronic respiratory failure, thoracic cancer, chronic heart failure)
- Significant improvement in quad strength and 6MWT
- Some weaker evidence of increased muscle mass
NMES for Knee OA in Elderly
- Moderate evidence than NMES alone or NMES combined with exercise improves isometric quad strength
Functional Electrical Stimulation (FES): example
- uses electrical stimulation to aid in functional movements
Example: TA stimulation during gait to assist with foot clearance; stimulation is triggered when heel leaves the ground
EMG Biofeedback: what is it and why is it used?
Tool for muscle retraining
- surface electrodes are placed over the target muscle
- voluntary activation of the target muscle results in MU action potential that can be sensed by electrode
- patient received immediate visual or audio feedback when the target muscles contract
EMG biofeedback: clinical use
INHIBITED MUSCLES
- e.g. VMO following a knee injury - patient gets immediate feedback when he/she is able to activate the target muscle
OVERACTIVE MUSCLES
- e.g. upper traps - patient gets immediate feedback that the muscle is over active during exercise and then they can adjust mechanics to “turn the muscle off”
Can NMES be used for lower traps or is it contraindicated?
- Concern: NMES may stimulate the intercostal muscles and effect breathing (do not perform on national exam - there are alternatives to NMES)
- Target: retrain lower trap activation, then use low intensity that is unlikely to case deeper muscles to fire.
- Precaution: pt with little muscle mass or hx of breathing problems
Trouble with intensity (sensory - pain)
Consider using a lower pulse duration
- Strength-Duration curve: shift to the left gives you more leeway between sensory, motor, and pain stimulation
- Intensity: only change during on-time so patient can give you immediate feedback
- Other: active muscle contraction when electrical stimulation is applied
