FES

Question 1

PHYSICS FUNDAMENTAL

Answer 1

FES builds a circuit where human body (nerves)

is part of the circuit

Question 2

PHYSICS EXPLAINED

Answer 2

‣ FES uses waveform that is
‣ “monophonic” (pulsed DC) OR
‣ “biphasic” (current moves in both
directions over time)
‣ In a graph of the current over time, the area
between the waveform and the axis
represents the amount of charge that moves above/
below the axis representing opposite
directions
‣ Therefore, an asymmetric waveform indicates
that charge builds up at electrodes over time

Question 3

PHYSIO AIM

Answer 3

Elicit a muscle contraction by stimulating the

motor nerves

Question 4

PHYSIOLOGICAL EFFECTS

Answer 4

‣ Stimulates muscle activity via selectively
depolarising motor nerves to generate a
contraction of the muscle fibres
‣ Short duration current allows for stimulation
of motor nerves compared to sensory nerves
or nociceptors
‣ FES uses a higher frequency (35-50Hz) than
recruitment for normal motor neuron (5-25
Hz)
‣ Causes all motor neurons to fire
simultaneously, therefore fatiguing faster
‣ Preferentially activates fast twitch fibres
which fatigue faster
‣ Requires an intact peripheral nervous system
to generate a contraction
‣ Used in daily life to replace lost function

Question 5

CONTRAINDICATION

Answer 5

Vicinity of uterus in pregnancy 
Over inbuilt stimulator (eg.
Pacemaker) 
Superficial metal
Open wounds 
Neoplasms 
Trans-cerebral or trans-thoracic

Question 6

PRECAUTIONS

Answer 6

Circulatory Insufficiency
Risk of dissemination
 Exacerbation of existing conditions
Unable to communicate
Sensory loss
Cognitive impairement

Question 7

Settings/Dosage

Answer 7

TIME:
* depends on
exercise
parameters

SURGE ON/OFF
Typically
5 secs ON/
10 secs OFF
RAMP
Typically 1 second

AMPLITUDE
Motor: to muscle
contraction

APPLICATION
Manual
Cyclic
Triggered
Controlled

FREQUENCY
Motor: 35-50 Hz

Question 8

indications

Answer 8

INDICATIONS
‣ Used in daily life to
replace lost function
‣ Upper and lower limb
function, bowel and
bladder function, or
respiratory function

Question 9

KEY POINTS

Answer 9

‣ Therapeutically used to facilitate, activate and exercise a
muscle
‣ Used with insufficient motor drive (< Grade 3/5)
‣ Applied as surface vs intramuscular and single vs. multichannel
‣ Ramp time permits gradual increase/ decrease in motor
unit recruitment to allow smooth contraction and release

• safety: Ensure current on ‘continuous’
  when turning up intensity
  Avoid possibility of turning up current while pulse is OFF, and subjecting the patient to a higher intensity than necessary.

Question 10

Why does the muscle fatigue quicker with FES rather

than a natural contraction?

Answer 10

FES causes all motor neurons to fire at the same time
and therefore fatigue faster. FES also preferentially
activates fast twitch fibres which fatigue faster.

Question 11

At which frequency does tetany occur?

Answer 11

35-50 Hz

Question 12

Why does FES use biphasic current?

Answer 12

It moves in both directions, so no accumulation of
charge occurs, which is safer for the patient. Prolonged
charge build up can cause electrode deterioration and
skin irritation via build up of ions near electrodes.

Question 13

What are 3 ways to maximise FES preparation to

minimise current needed to produce a contraction

Answer 13

1. Correct electrode placement. Simulating over the
   motor point requires the least amount of current to
   produce a contraction
2. Clean skin. No creams or lotions.
3. Reduce hair resistance (ie. shaving)

Question 14

Does the black or the red electode go over the motor

point?

Answer 14

Black goes over the motor point supplying the muscle

and the red goes distal to it.

Question 15

Why is it better to use larger electrodes?

Answer 15

It decreases current density which increases comfort