Electrical Currents for Muscle Contraction Flashcards
The use of electrical currents to produce muscle contractions in innervated muscles is called what?
neuromuscular electrical stimulation (NMES)
What 5 things can NMES be used for?
- Stroke
- SCI
- Sports-related injury
- Postoperative conditions
- Healthy athletes
What are the 5 things NMES-stimulated contractions can do?
- Strengthen muscle
- Improve cardiovascular health
- Retard or prevent muscle atrophy
- Reduce spasticity
- Restore function
What is the difference between muscle contractions produced by electrically stimulated action potentials (APs) and those produced by physiologically initiated APs?
- With PI contractions, the smaller nerve fibers (and thus the smaller, slow-twitch type I muscle fibers) are activated first
- With ES muscle contractions, the largest-diameter nerve fibers (and thus the larger, fast-twitch type II muscle fibers) are activated first
The large, fast-twitch type II muscle fibers stimulated via electrical stimulation produce what type of contraction? What are 2 other characteristics of them?
They produce the strongest and quickest contractions. However, they fatigue rapidly and atrophy rapidly with disuse.
The smaller, slow-twitch type I muscle fibers physiological initiated produce what type of contraction? What are 2 other characteristics of them?
They produce lower-force contractions that do not fatigue as easily and do not atrophy as easily
When is electrical stimulation useful?
When you want to specifically strengthen muscle fibers weakened by disuse
What should the patient do to optimize the functional integration of strength gains produced by NMES?
They should perform BOTH ES and PI contractions
Should rest times be long or short for NMES? Explain why…
Long rest times should be utilized due to the muscle fatigue
In regards to onset of contraction how do ES and PI contractions differ?
- PI contractions gradually increase in force in a smooth graded manner
- ES contractions tend to have a rapid, jerky onset
Why is ES onset rapid and jerky?
because all motor units of a given size fire simultaneously when the stimulus reaches motor threshold
ES strengthens muscle via what 2 principles?
- Overload
- Specificity
What does the overload principle state?
The greater the load placed on a muscle and the higher force contraction it produces, the more strength that muscle will gain
What type of contractions can the overload principle be applied to?
Both ES and PI
How can the load be increased with PI contractions?
by increasing resistance
How can the load be increased with ES contractions?
- Increasing the amount of current
- Adjusting pulse duration and amplitude
- Adjusting electrode size
- Increasing externally applied resistance
What does the specificity principle state?
Muscle contractions specifically strengthen the muscle fibers that contract
Because ES has more of an effect on larger, fast-twitch type II muscle fibers, what type of patient is it optimal in and why?
ES can be used post-surgically, post-immobilization to amplify and accelerate strength gains
What are 3 possible reasons why ES may amplify and accelerate strength gains in post-surgical patients?
- May enhance the quality of motor recruitment
- May carry over to improved performance of functional activities
- May initially have a force of as little as 10% of MVIC
To increase _____, higher-force contractions should be used
strength
To increase ______, prolonged stimulation with more lower-force contractions should be used
endurance
NMES plus voluntary exercise can increase strength in what muscle following TKA?
quadriceps
What 3 non-surgical orthopedic conditions can benefit from NMES? Describe how each can benefit…
- Osteoarthritis: decreases pain and increases strength
- Rheumatoid Arthritis: reverses muscle weakness and atrophy
- Patellofemoral Syndrome: increases VMO strength
E-stim can be used to increase strength and improve motor control in patients with CNS damage under what conditions?
as long as the peripheral motor nerves are intact
What 5 neurological disorders can benefit from NMES?
- Spinal Cord Injury
- Stroke
- Traumatic Brain Injury
- Multiple Sclerosis
- Cerebral Palsy
Gains can be made in neurological disorders through the use of NMES in what 3 ways?
- Muscle strengthening
- Increased general excitability of the motor neuron pool
- Sensory input cueing
General excitability of the motor neuron pool can be produced by ___ level electrical stimulation
motor
Sensory input cueing is necessary for what 3 things?
- Initiation of movement
- Activation of a muscle group
- Reflexive motor contraction
Sensory stimulation without motor level stimulation may also enhance what 2 things?
brain plasticity and cortical motor output
Can NMES reverse SCI damage?
No
NMES is used to do what 2 things in SCI patients?
- Counteract disuse muscle atrophy
- Improve circulation
What are the 5 conditions required for FES to be effective?
- it must produce a contraction of sufficient force to carry out the desired activity
- must not be painful
- must be able to be controlled and repeated
- the LMN, neuromuscular junction, and muscle must be intact
- the method of delivery must be acceptable to the user
What are the 4 benefits of when NMES is used for leg cycle ergometry, arm cranking, or rowing?
- Increase muscle strength and endurance
- Decrease muscle atrophy
- Increase energy expenditure
- Increase blood flow, oxygen uptake, stroke volume, and ventilatory rate
An implantable FES system is used to stimulate what 3 things?
- Phrenic nerve
- Abdominal and chest wall muscle
- Sacral nerve
Following stroke NMES stimulation of the agonist muscles do what?
- improve voluntary recruitment
- improve gait
- increase DF torque
- reduce agonist:antagonist co-contraction
- increase function
Following stroke NMES stimulation of the antagonist muscles do what?
- reduce spasticity
- improve strength
- improve function
How can NMES mimic an activity such as gait following stroke?
It can sequentially stimulate the agonist, then the antagonist, such that muscle contraction mimics gait
What are the benefits of NMES in children with CP?
- improves gait
- decreases spasticity
- increases function
- increases grip strength
- improves posture
What are the benefits of NMES in people with MS?
- improve walking speed when FES is applied to the peroneal nerve
- increases power and smoothness of movement
- reduces spasticity
Can NMES increase strength in healthy individuals?
Yes
*Inconsistent impact on functional performance such as squat jump height, counter-movement jump, vertical jump and sprint speed
Benefits are maintained for _ weeks after training with NMES
5
What are 5 other conditions in where NMES can be used for?
- Treatment of patients with swallowing difficulties
- Preventing muscle atrophy in astronauts in zero gravity environments
- Treatment of urinary incontinence associated with pelvic floor dysfunction
- Promote blood flow in healthy individuals with poor circulation
- Promoting venous circulation and reducing risk of DVT
What type of e-stim is used in denervated muscle?
Electrical Muscle Stimulation (EMS)
In denervated muscle, if the current lasts longer than __ milliseconds, the muscle will contract
10 milliseconds
EMS utilizes a ______ current
continuous
Ongoing EMS has what effect on denervated muscle?
It may retard or even reverse the atrophy and fibrosis of denervated muscle
What are the contraindications to NMES?
- Demand pacemaker or unstable arrhythmias
- Over the carotid sinus
- Venous or arterial thrombosis or thrombophlebitis
- Pelvis, abdomen, trunk and low back during pregnancy
- When contraction of muscle may disrupt healing
What are the precautions to NMES?
- Cardiac disease
- Impaired mentation or sensation
- Malignant tumors
- Skin irritation or open wounds
NMES utilizes what type of waveform?
Pulsed biphasic waveform
Where should the 2 electrodes be placed for NMES?
One electrode over the motor point and the other on the muscle to be stimulated. They need to be aligned parallel to the direction of the muscle fibers
Electrodes must be placed at least _ inches apart for NMES to work
2
How should the patient be positioned for NMES when movement is contraindicated?
The limb should be secured in the joint’s midrange to allow the patient to perform a strong isometric contraction in that specific range
How should the patient be positioned for NMES when movement is not contraindicated?
The limb does not have to be secured and the patient is asked to perform a strong isotonic contraction throughout the full range
What is the range of pulse duration for NMES?
150-350 microseconds
- Smaller pulse duration for smaller muscles - Longer pulse duration for larger muscles
As the pulse duration is shortened for smaller muscles, how will you need to adjust the amplitude in order to produce the same strength of contraction achieved in larger muscles (longer pulse duration)?
The amplitude will have to be increased
What is the frequency range for NMES?
35-50 pps which is strong enough to produce a smooth tetanic contraction
Will a frequency in the range of 50-80 pps increase strength?
Yes, it will produce greater muscle strengthening but also more rapid fatigue
What is the frequency range for NMES of small muscles?
20-30 pps is better tolerated
The on time for NMES should be between _ and _ seconds
6-10 seconds
The off time for NMES should be between _ and _ seconds
50-120 seconds
What should the ratio of on:off times be for NMES?
Initially the ratio should be 1:5, however this can be amended as the patient becomes stronger
What is the recommended ramp time for NMES?
1-4 seconds
What should the amplitude be for people without injury?
minimum of 50% MVIC
What should the amplitude be for patients recovering from injury?
Initially a 10% MVIC should be used, however this can be amended as the patient becomes stronger and more tolerant of treatment
How long should treatments be for muscle strengthening?
10-20 contractions or 10 minutes
How long should treatments be for muscle re-education?
Treatment time varies, however it should not be longer than 20 minutes
What are the 6 things you must document on after performing e-stim?
- Area treated
- Patient positioning
- Parameters
- Electrode placement
- Treatment duration
- Patient response to treatment
