Electrical muscle stimulation (EMS) uses electrical currents to cause muscle contractions and strengthen weak muscles. Different types of currents such as faradic and galvanic are used depending on if the muscle is innervated or denervated. A strength duration curve shows the relationship between stimulus magnitude and duration, and can indicate the state of a nerve lesion by its shape. Parameters like frequency, pulse duration, and amplitude must be set properly for safe and effective EMS treatment.

1. ELECTRIC MUSCLE
STIMULATION

2. Introduction
◦ Electrical muscle stimulation (EMS) is a type of electrotherapy stimulates a muscle
contraction using electrical impulses in order strengthen weak muscles, reduce
swelling, relieve pain and help heal wounds.
◦ Generally, electrical currents are classified as either being a direct current (DC) or an
alternating current (AC), depending on how the electrons flow.
◦ Classification,pulsed current, represents a type of current that has been modified to
produce specific biophysical effects.
◦ The terms “alternating” and “direct” describe the uninterrupted flow of electrons;
“pulsed” indicates that the electron flow is interrupted by discrete periods of no
electron flow.

3. ◦ Pulsed currents may flow in one direction, similar to a DC, or may have bidirectional movement, as
in an AC. Polyphasic currents are hybrids that contain multiple current types.
◦ The primary properties of electrical current are amplitude (intensity) and pulse/phase duration.
The amplitude is the maximum distance that the pulse rises above or drops below the baseline
(isoelectric point), the point where the electrical potential between the two poles is equal and no
current flow occurs.

4. Classification of electical stimulating of
current

5. Electrical Stimuli and normal behaviour
of nerves and muscle
◦ Electrical impulses to nerves which causes the muscles to contract mimicking the action
potential coming from the central nervous system. It may be applied during functional
movement or without functional movement.
◦ During normal physiological muscle contractions, the first fibers to be recruited are the slow-
twitch type 1 muscle fibers, and then later the large diameter muscle fibers, which produce low-
force contractions and are fatigue and atrophy resistant and the contraction is smooth.
◦ On the contrary, during electrically stimulated muscle contractions, the first muscle fibers to be
recruited are the large-diameter fast-twitch type 2 muscle fibers which produce the strongest
and quickest contractions, fatigue, and atrophy rapidly and produce jerky movements which is
why upon electrical stimulation by NMES long rest times should be provided between
stimulated contractions.

6. Parameters
◦ Frequency (Hz) is the number of pulses in one second (20-50 pulses per second)
◦ Pulse Duration (microsecond) for small muscles is approximately 150-200 and for
large muscles 200-300
◦ Ramp time is at least 2 seconds
◦ ON: OFF time ratio should be set in a way where off time is three times the on time
◦ Treatment time should be between 20 and 30 minutes
◦ The frequency of the sessions should be three times a week

7. Types of lesion

8. Process of Denervation
◦ Severe injury to the nerve causes damage to the nerve axon so that it is unable to support the
metabolic process of its distal part resulting in degeneration of the whole length of the new
fiber including the myelin sheath distal to the lesion.
◦ This process is called Wallerian degeneration.
◦ It takes as long as 14 days to degenerate.
◦ The distal section of nerve remains excitable and can conduct impulse before degeneration has
taken place.
◦ Because of this it may not be possible to make full assessment of the lesion till three weeks,
after suspected nerve injury.

9. Regeneration of Nerve
◦ The duration needed for full recovery will depend on the site of the lesion and the
length of nerve that has to regrow.
◦ The rate of regrowth is somewhat variable, being more rapid at first, up to 5 mm per
day, but is usually considered to be an average 1–2 mm per day.
◦ When there is degeneration of the nerve fiber the normal response is reduced or lost
and the changes become evident 3 or 4 days after injury.
◦ Changes in the reaction obtained on stimulation over the muscle, may be observed
before the end of first week.

10. Faradic current
◦ Faradic current is a short duration interrupted direct current with a pulse duration ranging from 0.1
to 1 ms with a frequency of 50 to 100 Hz.
◦ Faradic current is surged to produce tetanic contraction and relaxation of the muscle. Treatment
with faradic current also known as faradism.
◦ This frequency and duration cause contraction and relaxation in innervated (nerves intact)
muscles.
◦ It does not work on muscles that are denervated muscle; to cause the same effect a short pulse
duration would be required.
◦ When applying faradic stimulation, the stimulation of the sensory nerve can result in the patient
experiencing a pricking sensation due to the short duration of the pulse.

11. Types of waveform

12. Glvanic current
◦ It Is interrupted direct current has frequency 30 Hz with pulse duration 1Ms and more.
◦ This type of current used for muscle not have the nerve because of injury of the nerve. When
applying galvanic, the denervated muscle responds to this stimulus because of the long pulse
duration.
◦ The denervated muscle does not respond to faradic because pulse duration is short.
◦ The patient with faradic feel of burning sensation.

14. ◦ The physiological effect of faradic and galvanic are almost the same except faradic for
innervated muscle and galvanic for denervated muscle.
◦ Both current increase blood flow to the area treated that make the area slight redness due to
vasodilatation. Also, both current make contraction the muscle similar to voluntary muscle
contraction. To prevent fatigue the faradic allow the muscle to relax after contraction.
◦ The faradic and galvanic current increase metabolism and remove waste products and bring
more blood supply and nutrients to muscle thus increase demand of oxygen and nutrients to
the muscle.
◦ Electrical stimulation will re-educate muscle action.
◦ The electrical stimulation can help to minimize the extent of muscle atrophy.

15. STRENGTH DURATION CURVE
◦ Strength duration/Intensity duration curve shows the relationship between the magnitude of the
change of stimulus and the duration of the stimulus.
◦ The curve provides valuable information regarding the state of excitability of nerve lesion. It
should be done only after 21 days following nerve injury.
◦ Wallerian degeneration: Nerve degenerates proximally to nearest node of Ranvier and distally
throughout whole length. Debris is cleared by macrophagic activity. Process takes up to 21 days
to complete and is a preparation for regeneration.

16. ◦ Nerve regeneration— Regeneration of axons send out many branches one of which becomes
myelinated and continues to grow down the neural tube.
◦ Growth rate approximately 1 mm per day.
. Factor influencing rate of regeneration
. Age of the patient – Faster in younger age group
Site of lesion – Faster when lesion is more proximal to spinal cord.
Nature of lesion – Faster following spontaneous regeneration than following
nerve suture.

17. Instruction
◦ Receiving the patient
◦ . Knowledge of condition
◦ Preparation of trays
◦ Preparation of apparatus—Diagnostic electrical stimulator to be used.
◦ Positioning of the patient
◦ Position of Physiotherapist
◦ Checking for local contraindication
◦ Reducing skin resistance .
◦ Checking of apparatus
◦ Correct placing of pads and electrodes

18. ◦ Feel of current
◦ Instruction to inform if any burning occurs
◦ Warning not to touch anything
◦ Regulating current—Interrupted galvanic current
◦ Palpating tendon
◦ Winding up.
◦ Diagnostic stimulator to be used
◦ Interrupted galvanic current indicated

19. Shapes of curve
◦ Normal innervation— When all the nerve fibers supplying the muscles are intact, the strength
duration curve has a shape characteristic of normally innervated muscle .
◦ The curve is of this typical shape because the same strength of stimulus is required to produce
a response with all the impulses of longer duration, while those of shorter duration require an
increase in the strengths of the stimulus each time the duration is reduced.

20. ◦ Complete Denervation— When all the nerve fibers supplying a muscle have degenerated, the
strength duration produced is characteristic of complete denervation. For all impulses with
duration of 100 ms or less the strength of the stimulus must be increased each time the duration
duration is reduced and no response is obtained to impulses of very short duration. So that the
curve rises steeply and is further to the right than that of a normally innervated muscle .

22. ◦ Partial Denervation — As impulses shortened—denervated fibers respond less readily. So that a
stronger stimulation is required.
◦ With impulse of shorter duration—innervated fibers responses .
◦ When some of the nerve fibers supplying a muscle have degenerated while others are intact, the
characteristic curve obtained clearly indicates partial denervation.
◦ The right hand part of the curve clearly resembles that of denervated muscle, the left hand part
that of innervated muscle, and a kink is seen at the point where the two parts meet.

24. Rheobase
◦ The rheobase is the smallest current that produces a muscle contraction if the stimulus is of
infinite duration. In practice an impulse of 100 ms (0.1 s) is used.
◦ In denervation, the rheobase may be less than that of innervated muscle and often rises as
reinnervation commences.
◦ The rheobase varies considerably in various muscles and according to the skin resistance and
temperature of the part. The rise of rheobase may be due to fibrosis of the muscle.

25. Chronaxie
◦ The chronaxie is the duration of shortest impulse that will produce a response with current of
double the rheobase. The chronaxie of the innervated muscle is appreciably less than that of
denervated muscle, the former being less and the latter more than 1 ms if the constant-voltage
stimulator is used.
◦ With the constant-current stimulator the values are higher, but bear a similar relationhip to each
other. As practically seen the chronaxie of a muscle with 25% of its fibers innervated would be
the same as that of a complete denervated muscle.
◦ Thus, chronaxie is not a satisfactory method of testing electrical reactions as partial denervation
is not clearly shown.