2- Electrical Currents for Muscle Contraction

Neuromuscular Electrical Stimulation (NMES)

• The use of electrical currents to produce muscle contraction in innervated muscles

Does NMES require an intact and functioning nervous system?

Yes it does to work properly

What is NMES used for?

• Muscle strengthening

• Muscle education and reeducation

• Edema

Slow Twitch Type 1

• Innervated by small nerve fibers

• Activated first in physiological contractions

• Produce lower-force contractions

• Fatigue and atrophy resistant (for endurance)

Fast Twitch Type 2

• Innervated by larger diameter nerve fibers

• Activated first when muscle is stimulated electrically

• Produce strongest contractions

• Fatigue rapidly and atrophy rapidly with disuse (for explosive power)

Overload principle

A principle of strengthening muscle that states the greater the load placed on a muscle and the higher the force contraction it produces, the more strength that muscle will gain

Specificity Theory

Muscle contractions specifically strengthen the muscle fibers that contract

What is the best way to increase strength through electrical currents?

Higher force contractions should be used

What is the best way to increase endurance through electrical currents?

Lower-force contractions should be used

Orthopedic conditions treated by ES

• ACL reconstruction

• TKA

• Nonsurgical management of other orthopedic conditions

Neurological conditions treated with ES

Occurs via direct muscle strengthening or inc excitability of the motor neuron produced by motor level ES

• SCI - counteracts muscle atrophy and improves circulation

• Stroke - improves voluntary recruitment of motor units, proves gait, reduce agonist/antagonist co-contraction

• MS

• CP

• TBI

Functional electrical stimulation (FES)

• Application of an electrical current to produce muscle contraction during a functional activity

• Ex. stimulation of the anterior tibialis to cause DF during swing phase of gait

Contraindications for ES for Muscle Contraction

• Pacemaker or unstable arrhythmias

• Over the carotid sinus

• Venous or arterial thrombosis or thrombophlebitis

• Pelvis abdomen, trunk or low back during pregnancy

Precautions for Electrical Stimulation for Muscle Contraction

• Cardiac disease

• Impaired sensation or mentation

• Malignant tumors

• Skin irritation or open wounds

Parameters for ES for Muscle Contraction

• Waveform

• Electrode placement

• Pulse duration

• Pulse frequency

• On:off ratio

• Ramp up/down

• Amplitude

• Duration of treatment (10-20 min)

What is the MOST appropriate position for a patient using NMES?

• A position that allows the pt to contract their muscle in the direction of the contraction being created by the NMES

How should the electrodes be placed when using NMES

Parallel to the muscle fibers with one on the motor point

As the pulse duration (width) is shortened, how will the amplitude need to be adjusted to achieve the same strength of contraction?

The amplitude will need to be raised

What is MVIC?

maximum voluntary isometric contraction

What MVIC should be used when using ESTIM on a muscle without injury?

50%

What MVIC should be used when using ESTIM on muscles after post-op?

10%

What is the ratio used for beginning muscle contraction ESTIM?

1:5 with 6-10 seconds on and 50-120 seconds

What is the ratio for muscle contraction ESTIM to relieve muscle spasms (or to make them relax)?

1:1

How long does the pulse width need to be to stimulate a contraction in denervated muscle?

10 ms or longer