Neuromuscular electrical stimulation (NMES):
When you get injured one of the major issues is muscle
wasting. This is obviously caused by lack of exercise and also from pain
inhibition. The evidence shows pain has an inhibitory effect on muscle
activity. Particularly around the knee the activity of the Vastus Medialis
Oblique (VMO) is inhibited severely.
So how much of a problem is muscle wasting?
Muscle strength is found to decrease by between 2% to 6% in
the first 8 days of immobilisation (Muller,1970). After 2 weeks of not training
significant reductions in fitness can be measured & improvements can be
lost in months (Kisner & Colby 1996).
Muscle is inhibited when pain is around; this is due to the
nerve not firing correctly. This is very significant as to why NMES is
effective. In NMES the impulse is sent directly to the muscle making it
contract therefore bypassing this issue.
So what exactly is NMES?
Neuromuscular electrical stimulation (NMES) is basically an
electrotherapy modality that is used to affect and influence muscle activity.
It was originally used in elite sport to improve performance and more recently
NMES has moved into physiotherapy practice to help patients.
How does it work then?
It’s as it sounds, you are sending electrical signals
directly into the muscle to produce a contraction. You are able to target for
endurance or strengthening effects amongst other things. The way it works is
down to the different muscle fibre types the body has. The different fibre
types fire at different frequencies, which means the NMES can relatively target
them.
Here are the different muscle fibre types:
Slow Oxidative: Smallest and least powerful. Lots of
mitochondria and blood vessels. This means they use oxygen well and therefore
are highly resistant to fatigue. Posture muscles are full of these type and
endurance athletes usually have a high distribution of these.
Fast Oxidative-Glycolytic: medium sized and moderately
powerful. So are somewhere between Slow
Oxidative and Fast Glycolyyic, so athletes that need to have a combination of
speed and endurance will have more of this type.
Fast Glycolytic: Largest and most powerful. Few blood
vessels, contain lots of glycogen. They are anaerobic mostly and are designed
for short bursts of power but fatigue very quickly. Sprinter and power lifter will
have lots of these.
Neuromuscular electrical stimulation changes oxidative enzyme
activity, skeletal muscle fibre type & fibre size when used on the correct
settings to target the fibre types (Sillen et al 2013).
What does it actually do to the muscles?
The force of muscle contraction achieved is increased as the
intensity of the machine is increased (Ferguson et al 1989, Underwood et al
1990).
NMES optimally works alongside exercise for example, lifting a
weight with the NMES on. That being said NMES will still improve muscle strength on
its own, which is useful when your injury doesn't allow you to move much or
load you injury sufficiently to improve muscle function.
If you want to target endurance then you need to target the
slow oxidative muscle fibres. The NMES unit can be set to just contract these
fibres, which is good for endurance athletes and as these fibres atrophy the
most it is important to be able to target them.
If you want to target the Fast twitch fibres then you can’t
purely isolate them but you can get them contracting alongside the slow ones
and in doing this you can improve strength.
Overall NMES helps the following:
Prevention of disuse atrophy
Muscle re-education
Relaxation of muscle spasm
Maintaining or increasing range of motion
Prevention of venous thrombosis in selective muscles
immediately post-surgery
Increasing local blood circulation
Strengthening weak or injured muscles
So how do I use it?
Electrodes placement:
There are sticky electrodes that you basically stick onto your skin. These work best if both
electrodes are placed on the belly of the muscle that you are trying to stimulate. You will need the positive electrode on
the motor point of the muscle to get the best contraction with the lowest
discomfort.
Larger electrodes are better as there is less current density,
therefore less discomfort (Brooks et al 1990).
Settings for Muscle Strengthening:
30 - 35Hz @ 400 µs
4 sec ON / 4 sec OFF (minimum) but usually 10 sec ON / OFF
At least 15 mins alternate days, but usually 30 min / day
Need strong contraction (not just mild twitch) + voluntary
as well.
Settings for Muscle Endurance:
20Hz @ 400µs
2 sec ON / 2 sec OFF (minimum)
At least 1 hr day
Minimal contractions needed.
Settings for Very Weak Muscles / Marked Atrophy
10Hz @ 400 µs
2 sec ON / 2 sec OFF (minimum)
minimum 1 hr day
Minimal contraction needed.
What reasons mean that you can’t have NMES?
It is contraindicated in pregnancy however, there appears to
be no evidence for this except over the abdomen and lumbar spine of course.
Don’t use on patients with implanted electronic devices such
as pacemakers.
Don’t place electrodes around the front of the neck.
Don’t use over the Thorax in cardiac arrhythmias.
Don’t use in patients with peripheral vascular disease or
have a suspected DVT.
NMES can be used safely and effectively in patients with
cancer, chronic obstructive pulmonary disease, and heart disease. Recent
research has actually shed more light on the use of electrical stimulation in
these situations.
So what does the evidence say about the effectiveness of NMES?
Integrating NMES in the treatment of patients reduces the
total rehabilitation time (Gersh, 1992).
Below are some research examples for what NMES works for:
Knee:
Neuromuscular electrical stimulation & unsupervised home
range of motion exercises are cost effective after knee surgery (Levine et al
2013).
Electrical stimulation of vastus medialis muscle with physio
improves functional recovery post total knee replacement (Avramidis et al
2011).
Electrical stimulation of the quads supports the
regeneration process & results in a provable stronger reduction of the
atrophy (Mucha 2004).
Hand:
Electrical Stimulation: Beneficial effect on grip strength
& fatigue for RA patients with muscle atrophy of the hand (Pelland et al
2002).
Chronic disease:
NMES improves muscle weakness in adults with progressive
diseases such as COPD, chronic heart failure & cancer (Maddocks et al
2013).
Recovery rate:
Evidence is not convincing to support Neuromuscular
Electrical Stimulation (NMES) for enhancing recovery from exercise (Malone et
al 2014).
So as you can see it can be effective. I have seen reduction
in muscle wasting and faster strength and endurance returns in using NMES. So
if you have an injury then get booked in to help you to minimise the wasting
and get you back to full function faster.
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