Electrical Muscle Stimulation: The First Step to the First Step
Abstract
Muscle atrophy, which is the deterioration of muscle mass, affects everyone: astronauts in orbit,
injured athletes, people with motor degenerative diseases, and simply people who are growing of
old age. When the muscle is so weakened that the person can no longer do exercises on his/her
own, electrical muscle stimulation is used as a foundational tool. Electrical muscle stimulation is
the use of electrical currents to mimic muscle contractions to build basic muscle tone and
cognitive connection between the body and the brain so the person can begin to do simple
physical movements and exercises on his/her own.
Introduction
Just like your homework, muscle atrophy is one of those things that is hard to avoid as a
human. Muscle atrophy is the loss of muscle mass [1]. This happens because of low levels of
physical activity [1]. Although it is popularly used when speaking of injured athletes and
astronauts out in space, muscle atrophy can happen to anyone; some to greater degrees than
others [1].
Muscle atrophy is something that occurs with age, just as having decreased bone density
levels [2]. However, this is becoming more than just a problem that occurs with age. We, as a
Americans, live more sedentary lives as we acquire jobs that often require us to sit in seats for
nine hours a day [3]. But this is not just affecting adults; with the advent of technological
inventions such as the television and computer, children’s physical activity levels are also on the
decline [4]. The frightening rise of obesity is repeatedly spoken of in the news and media [5]. As
a side effect of gaining weight as couch potatoes, people are also losing muscle mass
inadvertently [6].
Physical therapists will often put people with muscle loss, who wish to regain that muscle
mass, on an exercise program with additive rehabilitation tools. [1]. One such tool is electrical
muscle stimulation (EMS) [7]. After long periods of inactivity, due to events such as an injury,
muscles become weakened, and must be “re-taught” how to contract [7]. Electrical muscle
stimulation causes the muscle to contract involuntarily, without cognitive help from the person,
via electrical currents [7].
Since electrical stimulation was discovered in 1971 by Italian physiologist, Luigi
Galvani, when he made a frog’s leg twitch by sending an electrical current through it,
bioelectricity began receiving widespread attention [8]. In the 1960’s, Soviet Union sports
scientists began stimulating their athletes with electricity, claiming performance improvement in
their athletes [8]. In today’s world, electrical muscle stimulation is commonplace in
rehabilitation and training, but far reaching in its contribution to mankind.
What are muscles and how do they create movement?
There are three types of muscles: cardiac, smooth and skeletal [9]. Cardiac muscles line
the heart and contract involuntarily [9]. Smooth muscles line the hollow organs, such as blood
vessels, and are also contract involuntarily [9]. Skeletal muscles, which will be the focus today,
are as the name implies, attached to the bones and voluntarily contract; they are responsible for
movement [9]. Skeletal muscles are made up of long fibers, and each fiber is made up of smaller
units that are made up of even smaller units (see figure 1) [9].
Fig. 1 Muscle fiber and subunits http://muscleandbrawn.com/learning-the-muscle-fiber-types/
Skeletal muscles can also be called striated muscles because of the arrangement of alternating
units [9]. When the muscle is at rest, these contractile units that compose the muscle are only
slightly overlapping [9]. According to the sliding filament model, muscles contract when these
units slide, overlap even more, and shorten (see figure 2) [9].
Fig 2. Sliding Filament Model
http://84d1f3.medialib.glogster.com/media/55/55000922a932e270df3c59187dd8b533ae6265265
5a9a3c8b82c054f6a67680e/muscle2-jpg.jpg
Muscle contractions occur when an action potential, an electrical impulse from a motor neuron
(nerve cell originating from the spinal cord), travels down a nerve ending and releases a
neurotransmitter (chemical that is able to send a signal to another structure) to a nerve receptor in
the muscle fiber [9]. This then causes an action potential deep inside the muscle, resulting in a
release of calcium ions, which allow the contractile units of the muscle to shorten and contract
[9]. Once all of the calcium ions are absorbed, the contraction stops and will not be re-activated
until another separate action potential occurs [9]. The muscle then relaxes and the sliding
contractile units return to their original position [9].
Alternative method of contraction: Electrical muscle stimulation
Normally, during physical exercise, the brain sends an action potential through the nerves
to the muscles for your muscles to contract [9]. However, an outside source of electrical impulse
can be used to mimic the action potential, causing your muscles to contract similarly, without the
message from your brain [10]. In electrical muscle stimulation, electrodes that emit electrical
currents are used in place of action potentials [11]. These electrodes are placed over the muscles
and cause the muscles to shorten and contract when an electrical current passes though [11]. The
flow of electrical impulse is not constant. It turns on and off, so that it imitates the way a muscle
both contracts and relaxes [11].
In the simplest form, an electrical current is passed through two electrodes, which is
called a channel [12]. One electrode has a positive charge and the other has a negative charge
through which electrical currents flow [12]. Electrical currents typically choose the path of least
resistance through which to flow [9]. Water is a great conductor for electricity, and this would
offer the least amount of resistance [9]. Of the body, blood contains the largest amount of water
[9]. Muscles have a far greater amount of water in them than fat, thus making them better
conductors [9]. The electrical currents from the electrodes flow through the water of the muscles
to stimulate the muscles and nerve [9].
The size of the electrodes can vary, and the usage is dependent on the size of the area one
wishes to cover [13]. Distance between the two electrodes from one another is dependent on the
type of contraction [13]. Closer pads lead to shallow specific contractions while farther electrode
lead to deeper generalized contractions [14]. An EMS unit typically has settings for changing the
frequency (pulse rate per second), pulse duration (time span of singular pulse), and amplitude
(intensity), which varies depending on the person and treatment [13]. People with more damaged
nerves and numbness will require high intensities to feel the contraction [14].
In a variation to this, there are inferential currents, which use four electrodes rather than
two electrodes for two channels instead of one [15]. The two channels are crossed at higher
frequencies and shorter pulse rates to reach deeper tissues [15].
Electrical Muscle Stimulation and Muscle Re-education
When electrical muscle stimulation forces the muscle to contract, it is creating basic
muscle tone because the muscle is being worked on [7]. This is very helpful in cases where the
muscle is so deteriorated that it is difficult for the patient to do basic exercise, such as bedridden
people [7]. Rebuilding basic muscle tone creates the foundation for such people to begin to be
able to do simple physical activities again such as walking [16]. This repetitive contraction also
strengthens and reconnects the cognitive link between the brain and the body to make these
movements, if the injury suffered did not damage the nerve roots of the spinal cord responsible
for controlling the part of the body desired [16]. The goal of electrical muscle stimulating in
muscle re-education is to rebuild muscle strength and motor connections in the body and
movement enough so that the patient is strong enough to use those muscles on his own and
return those muscles to the desired strength [17].
Electrical Muscle Stimulation Warnings
The purpose of EMS is to be used over areas with muscle or fat because that is where
there is medium for the current to flow through [18]. Thus, it should not be used over areas with
great electrical resistance, such over the spinal column [18]. Using EMS over areas with greater
resistance would require turning up the intensity greatly, which can lead to irritation or damage
to the skin or muscle [18]. Damage to skin or muscle can result in burns and bruises [18]. As
with most electronic devices, electric shock can occur from the pads or wires if the equipment is
damaged [18]. EMS should not be used over areas that are inflamed, injured, or containing open
wounds because that could further aggravate the damage [18]. Due to potential electromagnetic
interference, it has been advised that patients with pacemakers not use EMS for fear that it may
result in pacemaker malfunctions [19]. EMS should also not be used on pregnant women or over
the uterus because it is unclear what electrical stimulation can do to a fetus [20].
Controversies: Usage for Beauty and Cosmetics
In recent years, some companies have claimed that electrical muscle stimulators can
strengthen muscles without exercise [21]. The FDA has not cleared any devices for such
purposes [20]. Although EMS devices force the muscles to contract, there has been no data
showing that this will cause a change in body appearance without proper diet and exercise [20].
Although EMS does increase muscle strength in those with atrophied muscles, there has been no
evidence of it increasing muscle mass in healthy people [22].
Electrical Muscle stimulation has also been used for facial rejuvenation. Companies have
claimed that EMS reduces sagging, wrinkles, and lines on faces [23]. The FDA has not approved
of EMS devices as a tool for facial rejuvenation [20]. It is also dangerous to have electrical
stimulation near eyes if the intensity is too strong [23].
Conclusion
Electrical muscle stimulation has become a commonplace in physical therapy settings, as
it is a useful noninvasive tool for muscle rehabilitation. With our aging society and the rise of
obesity, muscle rehabilitation is becoming more typical. Some may view this engineered
invention as run-of-the-mill; there have been advancements to use it for tissues beyond the
muscles. Although there has non-substantial claims in the effectiveness of using electrical
stimulation for cosmetic purposes, electrical muscle stimulation is starting to be used on the
spinal cord for chronic pain and vagus nerve for epilepsy and depression. [24] [25] [26].
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