PRINCIPLES OF
THERAUPEUTIC CURRENTS
AND NEUROMUSCULAR
ELECTRICAL STIMULATION
OBJECTIVES
 Describe
the electrophysical principles
related to therapeutic currents;
 Given a therapeutic current, describe the
characteristics of the current;
 List and ratify the factors that affect
current conductivity;
 Identify the essential features of each
NMES, apply in a safe and correct manner
OBJECTIVES
 Describe
the physiological effect of
electrical stimulation;
 Given a clinical condition, justify the
choice of stimulation parameter and
protocol based on the physiological and
clinical effects
CONTENTS
 Basic
concepts of electrophysics and therapeutic
currents;
 Description and characteristics of therapeutic
currents;
 Basic features of the commonly used NMES
 Review of basic physiology of muscle and nerve;
 Application principles and selection criteria;
 Clinical indication and precaution
THERAPEUTIC CURRENTS
 Therapeutic
currents can broadly be defined
as electrical currents, produced by
electrotherapeutic devices, induced to the
body tissues to elicit certain physiological
/clinical effects. Neuromuscular electrical
stimulation (NMES) is the application of
electrical current to elicit a muscle
contraction
CLASSIFICATION OF
THERAPEUTIC CURRENTS
A continuous unidirectional flow
of charged particles (current)
Direct Current
Uninterrupted bi-direction flow
of current
Alternating Current
cps or Hz
Unidirectional or bi-directional
flow of current that periodically
ceases for a finite period of time
Pulsed Current
pps
DESCRIPTIVE CHARACTERISTICS
 PHASES
 Monophasic
 Biphasic
 Triphasic
 Polyphasic
SYMMETRY OF PHASES
 Symmetric
 Asymmetric
BALANCE OF PHASE CHARGE
 Balanced
 Unbalanced
QUANTITATIVE DESCRIPTIONS OF
PULSED AND AC
 Amplitude-Dependent
–
–
–
–

Characteristics
Peak amplitude
Peak-peak amplitude
rms amplitude
Average amplitude
Time Dependent Characteristics
–
–
–
–
Phase and pulse duration
Rise and decay time
Interpulse and intrapulse
period and frequency
QUANTITATIVE DESCRIPTIONS OF
PULSED AND AC
 Amplitude
and time-dependent
characteristics
– Phase charge
– Pulse charge
– µC
CURRENT MODULATION
– Amplitude modulation
– pulse duration modulation
– frequency modulation
 Timing
Modulations
– burst mode
– duty cycle
5s
20s
Duty cycle
20%
TERMINOLOGY OF
THERAPEUTIC CURRENTS
Shape
DC
Shape
Monophasic
Therapeutic
currents
Pulsed
Current
Shape
Sym
Biphasic
Balanced
Shape
Unbal
Shape
Asym
AC
Shape
Sym
Asym
Balanced Shape
Unbal
Shape
TYPES OF THERAPEUTIC
CURRENTS STIMULATORS
http://www.rs.polyu.edu.hk/rssyeung/ept2machine.html
TYPES OF THERAPEUTIC
CURRENTS STIMULATORS
Galvanic stimulators
 Produce continuous
direct current
 e.g PTU, Ten Pulses
Stimulators

NEUROMUSCULAR
ELECTRICAL STIMULATOR
 Produces
the effect of muscle nerve
stimulation
 “Faradic” type stimulators
 “Russian” stimulators
 High Voltage stimulators
FARADIC TYPE
STIMULATORS
 Faradic
current
 an asymmetrical
biphasic current with a
pulse duration of 1 ms
1ms
RUSSIAN CURRENT
 A 2500
Hz AC
modulated every 10ms
to provide 50 bursts
per sec.
10ms
interburst
10 ms
Burst
HIGH VOLTAGE
STIMULATORS
 A twin-spike
Waveform: monophasic
pulsed current
 pusle duration: 5-65s
 Freq: 1-120 pps
 Peak amp: 500 V
(2000-2500 mA)

5-65 µs
FUNCTIONAL ELECTRICAL
STIMULATOR (FES)
INTERFERENCE CURRENT
 Two AC
with slightly different frequency
from two independent low voltage AC
superimposes (interferes) on the same time
axis;
 The result is a unique pattern of amplitude
modulation “beat” with a beat frequency
of 1-100 bps.
ELECTRODES
 A conductive
materials that
serves as the
interface between
a stimulator and
the patient’s
tissues
TYPES OF SURFACE ELECTRODES
 Metal
electrode
 durable
 reusable
 inexpensive
 inflexible
 Carbonised
Rubber
 relatively
inexpensive
 fairly durable
 gel or water
required
 may cause skin
irritation
SPECIALISED PROBE
 Allow
point
stimulation
 location of motor
point
EFFECTIVE ELECTRODES
 With
low skin-impedance
 Uniform in current conductivity
 avoid skin irritation
 with uniform contact on treatment surface
 cost effective
SIZE OF ELECTRODES
 Current
density
inversely
proportional to
the electrode
contact area
ELECTRODE PLACEMENT
 Motor
point: a
point on the skin
overlying a
concentration of
terminal motor
nerve branches
METHOD OF APPLICATION
 Polarity
- relative charge (positive or
negative) of the terminals (electrodes) of an
electrical circuit at any one moment of time
 Cathode-gains
electrons and becomes
negatively charged
 Anode-loss electrons and becomes
positively charged
 Active electrode-cathode
MONOPOLAR TECHNIQUE
 The
active
electrode (cathode)
to the muscle
motor point
 An indifferent
electrode to
complete the
circuit
BIPOLAR TECHNIQUE
 Both
electrodes on
the muscle
 usually
muscle
for large
BIFURCATED TECHNIQUE
 Common
in HVG
machine
 electrode from same
polarity bifurcated
into two
 muscle with multiple
motor points
 composite muscle
action with different
muscles
ACTIVATION OF EXCITABLE
CELLS WITH THERAPEUTIC
CURRENTS
EXCITABILITY OF NERVE CELLS
 Resting
potential
– -70 mv
 Intracellular or
extracellular
stimulation, offset
the resting potential
 when membrane
potential reaches
threshold, AP
generated
Na+
++++++++++++
K+
------------------
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 +10 +20 +30 +40 mv
Action potential of muscle
Action potential of nerve
Threshold of muscle and nerve
APPLICATION PRINCIPLES
 In
electrical stimulation, current induced
must be of sufficient amplitude and
duration to bring excitable cells to the
threshold of deplorization
 SD
curve
STRENGTH DURATION CURVE
Pulse
amplitude
mA
Sub
threshold
Suprathreshold
2x mA
Rheobase
x mA
Chronaxie
Duration ms
A
C fiber
Motor fiber
Mixed peripheral nerve
inherent excitability of the nerve fibre
Site and location
Prickling
sensation
Sensory
Nociception
Peripheral
nerve
Skeletal mm
Motor
Therapeutic
current
Visceral mm
Denervated
Muscle fibre
Muscle
contraction
S-D CURVE OF DIFFERENT NERVE FIBRES

 C
Sizes
dependent!
Selective
activation
Pulse
amplitude
mA
Duration ms
FACTORS THAT AFFECT CURRENT
CONDUCTIVITY
 Electrode-skin
interface
 Ohm’s law V=IR
 Resistance=the ease or difficulty of a DC
passes through a material.
– the number of free electrons
– viscosity of the material
– temperature
 Impedance=
the ease or difficulty of AC
passes through a material.
HUMAN SKIN
 Poor
conductor
 Dry skin = 1 M ohm
 Wet skin = 1 K ohm
 The conductivity of human tissue depends
on the proportion of water content
–
–
–
–
skin 5%
bone 5%
fat
15%
muscle 75%
Clean
Wet
Warm
Site
MUSCLE FORCE GENERATION
 Types
 Type
of muscle fibres
I
– twitch duration 120 ms
0
 Type
II
– twitch duration 30-50 ms
30
60
90
120 ms
FACTORS DETERMINE MUSCLE
FORCE GENERATION
 Spatial
and order of recruitment
– (size principles)
 Temporal
summation
– Frequency
 Asynchronisation
vs Synchronisation
Twitch of contraction
0
1000 ms
Fused contraction
STIMULATION PARAMETERS
 Current
density (spatial recruitment)
 Pulse/phase duration (SD curve)
 Frequency (temporal summation effect,
twitch duration of Type I and II fibres)
 Waveform (comfort level and effective
current density)
 on/off cycle (physiological movement,
fatigue)
APPLICATION
 Selection
of electrodes
 Method of application
 Placement and inter-electrode distance
TREATMENT DURATION AND
FREQUENCY
 Duration:
number of contractions / total
time of treatment
 Frequency:
session of treatments per day
or week
Stimulation
parameters
Application
Duration
CLINICAL APPLICATION
 Muscle
strengthening in healthy subjects
 Treatment of disuse atrophy
 Muscle re-education and facilitation
 Increase range of motion
 Functional Electrical Stimulation (FES)
MUSCLE STRENGTHENING IN
HEALTHY SUBJECTS
 Yakov
Kots (Russian technique)
 Current
 Amplitude
 On/off
cycle
 Session
 Result
2500 Hz, modulated to 50 bursts
110-130% of MVIC
10 s / 10s
3/52
3-40%  in strength, 3-4/52
CLINICAL CONSIDERATION
 Phase
duration
 Waveform
 Current
 Amplitude
 on/off
20-1000 s
rectangular or subject
preference
burst modulated AC
maximum tolerable
10-15s / 50-120 s
CLINICAL CONSIDERATION
 Method
of application
– depends on muscle size, group
 Contraction
 Duration
 Frequency
isometric/concentric
10x3
3/52
DISUSE ATROPHY
 Is
there a selective loss of muscle fibre in
disuse atrophy?
 How would that affect your treatment
plan?
A SUGGESTED PROTOCOL
Severe
Moderate Minimal
Freq
3-10
10-30
30-50
On
5
5-10
10-15
Off
25-50
20-30
10-30
Duration
5-10
15
15
INCREASE ROM
 Causes
 Single
channel
 Dual channel
MUSCLE RE-EDUCATION AND
FACILITATION
 Re-establish
voluntary control of body
positions and movement following injuries
that affected either both the afferent,
efferent neural pathway or the central
control centres in the motor and premotor
cortex
FES
SAFE AND PROPER
APPLICATION
 Selection
of proper stimulators
Output
amplitude
programming
Portable
No
of
vs
channels
Stimulationline-powered
Parameters
Fine
adjustment
Safety
features
SAFE AND PROPER
APPLICATION
Documentation
Current
intensity
Electrode
placement
Proper
Decrease
skin
skin
sensation
impedance
test
Stimulation parameters
CONTRAINDICATIONS
 Patient
with cardiac pacemaker
 Area of pregnant uterus
 Treatment of open wounds or skin lesions
 Acute inflammatory conditions
 Inability to communicate
 Benign / malignant tumours, T.B.,
osteomyelitis
OBJECTIVES
 Describe
the electrophysical principles
related to therapeutic currents;
 Given a therapeutic current, describe the
characteristics of the current;
 List and ratify the factors that affect
current conductivity;
 Identify the essential features of each
NMES, apply in a safe and correct manner
OBJECTIVES
 Describe
the physiological effect of
electrical stimulation;
 Given a clinical condition, justify the
choice of stimulation parameter and
protocol based on the physiological and
clinical effects