Chapter 7 Rehabilitation Physical Modalities 149muscle fibers are recruited, but may also result
in greater discomfort.
Pulse duration
Pulse duration, or pulse width, is the time of
one pulse and is measured in microseconds (μs).
Larger pulse durations can require less current
amplitude to achieve muscle contraction but
may also stimulate more pain fibers.
Frequency
Frequency, or pulse rate, is the number of pulses
per second and is measured in hertz (Hz).
Strong muscle contractions are often elicited
with frequencies of 60 to 100 Hz. Higher fre
quencies may increase muscle fatigue (Gondin
et al., 2010) and thus limit the patient’s ability to
participate in active exercise following NMES.
On/off cycle
The on/off cycle describes the time that current
is being delivered and the time that current is
stopped. Both are usually measured in seconds.
The duty cycle is the ratio of on‐time to the total
cycle time. As the on‐time lengthens, or if the
off‐time is insufficient to provide adequate rest
between contractions, muscle fatigue becomes
more likely.
Ramp
Ramp is the time during which the current is
gradually increased or decreased to improve
patient comfort. It is usually measured in sec
onds. A longer ramp time may be required for
patients affected by spasticity, but sufficient
time at peak intensity must be ensured to pro
mote strength development.
Mode
Most NMES units have two channels and offer
three treatment modes: constant, in which the
current is delivered without breaks; simultane
ous, in which the current is delivered according
to the on/off settings for both channels concur
rently; and alternating or reciprocal, in which
current delivery is still based on on/off settings
but the timing between channels can be adjusted.
Evidence supporting the use of NMESTherapeutic effects on pain
There is evidence that NMES use can reduce
pain, especially when the discomfort is related
to orthopedic issues such as knee osteoarthri
tis (Laufer et al., 2014) and patellofemoral pain
(Glaviano & Saliba, 2016). A 2015 study by
Demircioglu and colleagues found that the
addition of quadriceps NMES to a standard
rehabilitation program following total knee
arthroplasty resulted in significantly improved
pain scores as compared to patients who
received the rehabilitation program alone
(Demircioglu et al., 2015). The exact mechanism
of pain reduction is not entirely understood—
short‐term improvements may be related to
concurrent stimulation of sensory nerves, or
the immediate improvements in muscle acti
vation and resultant better kinematics during
functional activities (Glaviano et al., 2016).
More lasting effects may also be due to
increased muscle strength promoting more
normal joint mechanics, thus reducing addi
tional joint stress and further damage.Therapeutic effects on tissue healing
and protection
While many studies exist demonstrating the
ability of electrical stimulation to promote tis
sue healing, the majority employ waveforms
other than those typically used in NMES, such
as high‐voltage pulsed current (HVPC) and
direct current (DC). These waveforms will not
be covered in this chapter; the reader is again
referred to other sources for further informa
tion (Ud‐Din & Bayat, 2014; Hamm, 2015).
NMES can be used to promote healing of
some tissue types, however, such as peripheral
nerve. Willand and colleagues found that fol
lowing tibial nerve transection and repair in
rats, daily NMES of the gastrocnemius (via
implanted, intramuscular electrodes) resulted
in significantly greater numbers of re‐inner
vated motor units as compared to untreated
muscles (Willand et al., 2015).
In terms of tissue protection, NMES can be
effective in the management of venous disease
(Ravikumar et al., 2017; Williams et al., 2017),
and there is increasing evidence toward its use