EMS Theory

Expert Discussion Advanced Sports Sciences
1

This is the first installment in a series of postings on EMS theory. Subsequent postings will deal with current and physiology of the muscle.
Hystory
Electricity applications for health go back several thousand years. Electric eels were used in the Roman civilization to cause current in the human body to cure ailments.
In 1791 Luigi Galvani documented that electric current caused muscle contraction in the legs of a dead frog; although the mechanism of why electricity caused muscle contraction was misunderstoodm it started great scientific interest. During the 1800’s seminal research established scientifically the principles of muscle contraction that are still used nowadays. At the beginning of the 1900’s Weiss and the Lapicques introduced the principles of rehobase and chronaxe; these concepts are still widely used to conceive stimulation protocols in our days.

At the same time electrostimulation became a mainstream therapy method. In the 1990’s the miniaturization and affordability of electronics allowed the wide experimentation of new protocols, a flurry of research and sport application validation at the highest level especially in Europe. Protocols based on square waves improved in quality and superseded the protocols invented by Kots (aka Russian currents).

2

Let’s first clarify a few basics concepts about electricity, to clear misconceptions and misunderstandings about how EMS works.
Electrical Interaction and Conductivity
There are two kinds of electrical charge, called by convention positive (+) and negative (-). Positive charges repel each other and are attracted by negative charges and vice versa. When a generator concentrates charges of one type at at one point and charges of the other type at another point, if there is a conducting material in between, the charges will tend to flow from one point to the other. The convention is that electrical charges flow from (+) to (-); the flow is called current intensity (amount of charge flowing in one second). For our pusposes current intensity is measured in Ampères or A for short, and denominated with the letter I. In electrostimulation applications, it is customary to measure intensity in thousandths of A or milli-Amps, i.e. mA.
The force that drives the flow of charges, i.e. the force that drives the current, is called electric potential, and it is measured in Volts, or V for short. The electric potential will distribute itself differently depending on the conductor (i.e. the muscle), and this distribution will determine how the current will distribute itself around, and where it will concentrate itself. The distribution of electric potential is called electrical field.
An important property related to an electrical field is called electrical conductivity. This property determines how easily a charge will move between two points in an electric field. Rather than referring to conductivity, it is preferable to refer to the opposite concept, i.e. the resistance to the passage of a current in an electric field. The resistance is denominated with the letter R, the unit of measure is the Ohm (abbreviated by the greek upper-case letter omega).
The relationship between the three physical concepts associated with electricity is called Ohm’s law:
V= I x R
This means that, if the resistance R stays the same, when we increase the voltage V, the current intensity I increases proportionately too, and vice versa with decreasing values.
Thus if we stick two electrode pads on a limb and we connect them to a generator, the limb will oppose a certain resistance R to the current passage. If we want to obtain a certain current intensity I, we will have to generate with the electrostimulation device a voltage given by Ohm’s law.
The way current will distribute itself will depend on the electric field caused by the pads. In general the field will be more intense closer to the pads and on the surface of the limb, and weaker as we go deeper into the limb’s tissue. Therefore to circulate current deeper into a muscle you need a higher voltage.

3

Good basic lesson…

But how current can go deeper in the muscles depend from kind of signals (wave) too and not only from voltage.
The major problem with basic ems wave, common to compex and globus is their tetanic effect on muscles.
New age of ems don’t cause any tetanic effect and you can move during stimulation at any kind of intensity, voltage, frequencies.
There are some device can do this, one is ARP.
This is an important point, because draw the limit between simple “electrification” of a muscle and real CNS/neuromuscular stimulation with complex adaptation responce.
Russian stim was the past, compex or globus and similar are the present, but aARP and ARP like device are the future.
Personally I’m toward the future, and you?

4

I don’t agree that only the type of current will determine the depth of penetration. It’s a matter of “spill over”. Current maximally contracts fibre and then spills over to the next and next etc until deep fibre is involved, provided the wave form is tolerable enough to allow for enough stim,ulus to be applied. The effects of various wave forms can have different effects and may or may not promote tetany, as you say.

5

Is this aARP or ARP machine designed for the Relaxation of the muscles (ie TENS) and not the Strength as in EMS?
so that gives us 3 x
TENS
EMS
ARP

jamirok, could you perhaps start a thread, just like this one, giving us a run down on the New age ARP etc?

6

I would appreciate it if comments could be posted in the parallel thread for comments “EMS Theory Comments”. It will help readibility of this primer on EMS Theory, and allow quick reference of future installments.

7

Effects of Current Passage
Current passage is the movement of electric charges along a conductor. These charges can be in the form of free electrons, which have a negative electric charge. Free electrons in an electric field can move from one atom to the next attracted to the electric pole of opposite sign. Also atoms with one extra electron, called negative ions or anions, can move in the same fashion. Alternatively, an atom without one of its electrons, called a positive ion or cation, could move in an electric field toward the negative pole.
Salt (NaCl) dissolved into water promptly creates ions Na+ and Cl¯. If we place two electrodes connected to a generator in the water, the resulting electric field, tugs the Na+ cations toward the (-) electrode, and the Cl¯ anions toward the (+) electrode, and we have current passage. This is the reason why water conducts electricity, because there are always some traces of salt dissolved in it.
This current passage also results in the accumulation of the respective ions and cations at the electrodes. It eventually results in the electrochemical phenomenon called electrolysis, which produces Hydrochloric Acid (chemical formula HCl) at one end and Sodium Peroxide (chemical formula NaOH) at the other end. This is not good news for conducting current through the skin, because living beings’ cells contain water and various salts. In short if we subjected body tissue to electric current flowing in the same direction, soon there would be enough concentration of these chemicals to affect the skin; they react with proteins of the body tissue, and will cause chemical burns. However, if the current is of short duration, and its direction is periodically inverted, the chemical reaction is reversed at each cycle and its effects are neutralized.
Another property of an electric field is its distribution. The stronger the field the more in depth in the tissue it will go, and the more muscle fibers it will affect. We will see with more detail later, that this is the reason why a higher-intensity current stimulation will affect the muscles in a stronger way. This is important to keep in mind because many mistake the cause of this effect, and are lead to wrong conclusions. In other words, more current does not cause a stronger contraction of the same muscle fiber, but the more intense the current, the deeper the electric field, and the more muscle fibers will contract.

8

The muscle and its motor fibers
The main charcteristic of a muscle is that of shortening and moving the skeletal structure attached to it. In electrostimulation training we always refer to voluntary muscles we use for every day’s movement and sport.

A muscle is composed of muscle-fiber bundles; each muscle fiber in this bundle is composed of smaller elements called sarcomeres, each capable to contract. Muscle cells are cylindrical, with diameters of the order of magnitude of a thousandth of an inch (between 1/100 and 1/10 of mm), and length in the range between a fraction of an inch to an inch. The fiber receives a signal to contract from the the axon through a synapse.

The axon is the extremity radiating from the neuron of which it is part, and the synapse is the interface between the axon and the muscle fiber. Contractions are directly caused by myosin chains which are part of the fiber, and are in bundles called sarcomeres. Force is produced by myofibrils, which are chains of sarcomeres running from one end of the fiber to the other.

Energy for contraction comes from metabolism of fats and sugars. The amount of force production depends on the cross sectional area of the muscle, and is about 3-4 kg/cm2. Contraction speed and excursion are related to the fiber length.

A motorneuron may have a hundred or more axons, and therefore is responsible for the contraction of the same number of muscle fibers. A single motorneuron, with all the fibers it controls, is called a motor unit. As the brain’s signal for contraction increases, it both recruits more motor units and increases the firing frequency of those units already recruited. During a maximal voluntary contraction, it is unlikely that all the motor units (thus muscle fibers) are activated (according to Kots, at most 60-70%).

When the Central Nervous System (CNS) decides to activate a motor unit (MU), an electrical signal propagates from the CNS to the MU. This electrical signal travels at a speed between 3 and 100 m/s. The signal hops from one nervous cell to the next in a very rapid sequence. During this event each cell changes its polarity in thousandths of a second. Each nervous cell in its rest status is charged positively outside and negatively inside; the difference between the two is called action potential and its value is around 70 mV.

If an electric stimulation alters the action potential beyond a threshold, a series of electrochemical events will be triggered inside and outside the cell that will propagate the electrical signal to the next nervous cell. These events involve Na+ and K+ ions.
The nervous cell that innervates the muscle through a neuromuscular plate is able to pass its signal via the neurotransmitters acethilcoline.

The motoneuron may have several axons, and each one innervates a muscle fibers. Therefore when the signal arrives to the motoneuron, all of the fibers connected to it will get activated by the neurotransmitters. Early on in electrostimulation research it was discovered that what caused the excitation of the nerves and of the muscle fibers were two characteristics of the current: the amount of current, and the sudden change of its intensity. It is very important to understand what causes a contraction; not only a sudden increase of current will cause a contraction, but also a sudden decrease will cause it.

Stimulation can also be direct or indirect. Direct stimulation is defined as the stimulation that triggers directly the muscle fiber. Indirect stimulation is defined as the stimulation that excites the nervous cells, which will in turn trigger the contraction of the muscle fiber. Normally an indirect stimulation is better, because it causes the nervous fibers to affect more motor units, and it generates a stronger contraction.

9

TRAINING
With training we refer to the adaptation of the body to external physical stimuli. Living organisms posses the capability to stay in equilibrium with the environment. This property is called omeostasis, and is attained by the body by changing some of its characteristics: body temperature, heart beat rate, concentration in the blood of naturally produced substances, are all manifestations of omeostasis.
General Adaptation Syndrome
This term, describes all sorts of body’s reactions to a stress, including a sport stress. Training can be considered as a stressor to produce an adaptation for the targeted sport activity. The whole body is involved in this response.
In general we can observe the following sequence:
• Training stimulus
• Fatigue and performance decrease
• Progressive recovery from fatigue, and return of performance capability.
• Increase of performance capability above the initial level, thanks to body adaptation.
Adaptations and Changes Induced by Training
Training-induced adaptations include the following.
• Anatomical changes: heart size, i.e. hypertrophy; size of skeletal muscles; body fat decrease.
• Structural changes: mitochondrial changes; muscular fibers of type II into type I.
• Biochemical changes related to enzyme activity.
• Functional changes: O2 consumption; heart flow; recruitment of motor units.

In general all concepts to define and characterize voluntary training are valid for EMS training. Therefore it is recommended that you plan your training carefully. For this forum on speed training Charlie Francis advice is generally the best. However, if your set your training goals on different sports or fitness activities, the EMS training regimen should be changed accordingly.

Therefore one may look at EMS in terms of all of the following
Training Load
The training load is in general defined by the quantity of exercise and by its intensity (speed, power, frequency).
Load Specificity
Low frequencies for Endurance and higher frequencies for Explosive power cause metabolic and physiologic changes completely different from each other.
Frequency of training
It is necessary to stimulate the selected organ repeatedly, at regular intervals.
Load Progressivity
Training loads have to be continually changed, as a function of the evolving physical condition of the athlete.
Continuity
Training should not be interrupted, but continued in several cycles, since adaptation is reversible.
Variety
This principle is to utilize several training means to improve the sport performance.
Individuality of Loads
Each individual athlete is unique and responds to training differently. Therefore EMS training has to be conceived individually, even considering timing for the same athlete (season) to ensure the best result.
Sarcomeres
An increase of the number of sarcomeres in the muscle fiber can be done in the following ways
• In parallel: increasing the number of sarcomeres parallel to each other will increase the cross section of the muscle, and the force it develops.
• In series: the shortening of sarcomeres attached to each other as in a long string, determines the shortening of the muscle fiber; if the number of sarcomeres can be increased the sortening will be greater, and the speed of contraction will increase too.

NERVOUS FACTORS
Recruiting
In voluntary muscle activation, the number of muscle motor units and percentage of muscle fibers increases with the load on the muscle. Therefore voluntary muscle-fiber recruitment goes in progression according to their size: first smaller-size fibers, then larger fibers. Because slow-twitch muscle fibers (type I), are smaller than fast-twitch fibers (type IIa and IIb), a slight load will recruit only slow fibers, and a high load will recruit both slow- and fast-twitch fibers.

It will be explained in later sections, how EMS disrupts this recruitment order and indiscriminately activates neurons. Therefore EMS, with the proper current intensity, obtains a much higher recruitment and training effect. What discriminates in EMS between the different types of fibers is frequency.
Frequency
Frequency is the number of times per second the motoneurons are excited. A higher frequency is generally associated with higher force (because of the way each subsequent twitch adds to the previous one).

10

Electric Current’s Biological Effects
There are different effects caused by electric current, some wanted and some unwanted.
Thermic Effect
As it traverses a conductor, electric current transforms its energy into heat. To put this into perspective, a typical high level explosive-force program will produce approximately 0.5 W on average (at 50 mA), which will be dissipated through the muscle fibers. (Note: 120 Hz, 450 μs chronaxie, 2000 Ohm muscle resistance which is typical of quadriceps muscles)
Chemical Burn
Particular electrical characteristics may cause chemical changes in the tissue traversed so as to cause a localized caustic reaction and a burn. However, modern EMS devices reverse the direction of current passage at each pulse which reverses the chemical reaction, eliminating this effect.
Galvanic Effect
Electric current facilitates the movement of ionized molecules. This is utilized for the subministration of therapeutic drugs specifically prepared in ionized form.
Eccitatory Effect
Some tissue can be excited by the passage of electric current. This can be done directly at the muscular level bypassing the nerves innervating the tissue in question, or indirectly exciting the nerves that innervate the tissue to be excited. The latter is the focus of this digest.

The next post will introduce the concept of electrical potential in a nervous cell.

11

Membrane Potential at Rest
Organic tissue is characterized by electrical charge in it. The cell membrane, known as sarcoplasmatic membrane, has electrochemical mechanisms that manage to keep negative charges inside, and positive charges outside. The accumulation of charges creates an electrical field across the membrane, which as any electrical field, is characterized by an electric potential. Each living cell is characterized by this potential, which is known as membrane potential. Its value at rest is different from the value during excitation.

Purpose of the Membrane Potential
The membrane potential acts as a filter. If the stimulation is small it cannot penetrate it and nothing happens. If the stimulation is large enough, it can overcome the membrane potential, penetrate inside the cell and activate it. Therefore it filters out signals that are not strong enough.

Threshold Level
The value of the electric potential, which determines whether signals are strong enough or not to be further transmitted, is the threshold value. Both muscular tissue and motoneurones have a threshold potential of -55 mV (milli-Volt). However, their rest values are different: -70 mV for nervous tissue and - 90 mV for muscular tissue. This is the reason why it’s easier to stimulate muscle through their nerves.

Action Potential
When a stimulus decreases the membrane potential below its threshold value the cell membrane inverts its polarity. That is, as soon as the membrane potential is lowered from -55 mV to a value closer to zero, the membrane triggers an automatic ion-exchange mechanism across, which switches the membrane potential from negative to positive. This polarity inversion is called Action Potential.

Purpose of the Action Potential
The Action Potential acts as the messenger of a nervous signal. The polarity inversion switches the membrane of the next cell below its threshold level; this in turn causes another action potential in the next cell, and so on as in a chain reaction.

Sequence of Action Potential Generation
[ul]
[li]At rest the membrane potential is -70 mV.
[/li][li]External preturbation, i.e. stimulus, changes the membrane potential to -55 mV.
[/li][li]Beyond the threshold value the ion exchange mechanism triggers polarity inversion, i.e. the action potential, which is transmitted along the nervous fiber.
[/li][li]The action potential excites the membrane of the next cell, propagating the action potential mechanism to the target fiber.[/ul]
[/li]
What if the Threshold is not Reached?
If the initial stimulus does not reach the threshold value, there is no transmission of action potential, and the stimulus causes only a local effects.

In the next post we’ll take a look at Electrostimulation-Induced Contraction

12

Electrostimulation-Induced Contraction
Voluntary skeletal muscle contractions result from impulses commanded by the Central Nervous System (CNS) and transmitted through the nerves as electrical signals and eventually recruiting the desired muscles. The same can be achieved starting from an external electric impulse replacing the voluntary signal.

Tissue Sensitive to Induced Electrical Stimuli
Electrical impulses activating nerves are similar to electrical impulses activating muscles. Therefore one can decide whether to stimulate nerves and indirectly stimulate the muscles, or directly stimulate the muscles. However, there are differences between the two.

Direct Stimulation through Muscle Fibers
Direct stimulation of the muscle fibers bypasses all the rest of the CNS. However, this choice, even though possible, activates the muscles as if in a lab setting, by themselves and a bit out of of context, which is less conducive to training.

Difference between Rest and Threshold Potentials in a Muscle
The other important factor is that the difference between rest potential and threshold of muscle fibers, i.e. the difference between -90 mV, and -55 mV, is 35 mV. In other words the electrostimulator will have to overcome this difference to stimulate directly muscle fibers.

Difference between Rest and Threshold Potentials in a Nervous Fiber
The membrane potential of nervous fibers at rest is -70 mV, and the threshold to trigger an action potential is -55 mV. Therefore to excite nervous fibers it is necessary to overcome this difference, which is only 15 mV. Comparing this value to the 35 mV calculated for muscle fibers, the difference is huge: one will need 57% less potential to stimulate nervous fibers.

Applying Electrostimulation on Nervous Motor Units Fibers
The diameter of motor nervous fibers is larger than other nervous fibers’. They are also characterized by an insulating liner that allows for faster transmission of action potentials, insulation from outside impulses and a very precise selection of which fibers are going to fire. This insulation effect tends to insulate nervous fibers even from the stimulus of an electrostimulator. Fortunately there is a gap just before the nervous fiber reaches the muscle, and from here it is possible to send an external electrical impulse to the muscle. In addition the neuromuscular plate is situated on the muscle surface, closer to the outer skin. Therefore the electrical signals to stimulate the muscle do not need to be to strong, and it is possible to limit side effects.

Position of the Neuromuscular Plate
The neuromuscular plate is present on the whole surface of the muscle. However, it is more concentrated where the muscle reaches its maximum cross-section.

Similarity between Neuromuscular Stimulation and Direct Physiological Stimulation
Stimulation performed on nervous fibers, utilizes the same physiological mechanisms to transform nervous impulses into chemical impulses. Therefore all the physiological effects that would happen with voluntary stimulation and training of the same tissues take place.

It is also more convenient, as seen in a previous paragraph, to stimulate muscle fibers indirectly, through the nervous fibers, because of the lower membrane potential change needed (15 mV vs 35 mV needed for direct muscle stimulation).

Another factor that makes it even more convenient is greater comfort. The lower potential difference required means that also nerves carrying pain (nociceptive nervous fibers) are stimulated less.

Consumer Products for Electrostimulation
Most electrostimulator commercially available are designed for indirect stimulation. They are certified by the FDA in distinct classes of use: either without prescription for muscle-training-only purposes; or for therapy use with medical prescription.

Direct electrostimulation is reserved for special cases of therapy, under the guidance of a doctor or authorized practitioner.

The Mechanism Inducing Muscle Stimulation is Identical to a Voluntary Contraction
Once the electrical stimulus reaches the nervous tissue, it changes the membrane potential from its rest value at -70 mV to its threshold of -55 mV. The action potential generated propagates along the nervous fiber similarly to what happens for a stimulus generated by the CNS. The impulse arrives to the interface between the nerve and the muscle fiber, i.e. the synapse, where it is transformed in a chemical impulse.

The contraction at this point is regulated naturally in exactly the same mode that a voluntary contraction would be regulated. Therefore a voluntary and an involuntary contraction induced by electrostimulation are regulated by the same exact mechanisms and produce the same physiological effects, including muscle adaptation and training effects.

13

When Muscle Fibers are Stimulated Directly

Direct stimulation of muscle fibers is possible, even though one would need special electrostimulators, capable to supply a sufficient quantity of current and in the right place, bypassing the nervous fibers. For sport training this is never necessary, because it is more comfortable and easier to stimulate indirectly.

However, there are situations in which direct stimulation may be convenient or even irreplaceable. This is done for therapeutic or aesthetic reason, and it is mostly utilized when the nervous fiber is interrupted.

Electrostimulation for Therapy
Electrostimulation can be used for therapeutic reasons, to speed recovery of atrophied muscles.

In case of neuro-muscular damage, in which voluntary muscle movement is impaired, it is possible to contract the affected muscle through electrostimulation. Involuntary contraction in turn will help to maintain muscular tone, and may help the healing process of the damaged nerves.

Electrostimulation for Denervated Muscles
Denervated muscles are mentioned here, but are not an objective of this digest.
Electrostimulation can also be used as a therapy for denervated muscles, i.e. voluntary muscles that cannot be contracted voluntarily anymore. The therapy may have the objective of maintaining the tone of a muscle that cannot be exercised otherwise; or it may have the objective of regaining some voluntary control of the muscle. However, the properties of denervated muscles are very different from those of innervated muscles, and require particular programs, application protocols, and knowledge for the therapy to be effective.

Electrostimulation for Aesthetics
The toning effect of electrostimulation is used by those who want to improve particular appearance qualities related to the tone of the muscle.

The next post will start dealing with currents and the parameters that affect stimulation.

14

Currents

To obtain the desired contraction effect of electrostimulation, the current level will have to reach a compromise between a high enough current level to generate a strong contraction, and limited enough to exclude undesirable effects.

The current will have to be high enough. The excitation of the muscular tissue will be maximum when the electric current suddenly changes from zero to a certain value, and also when it suddenly changes from that value to zero.

Muscle fibers also have adaption capability, which means that they will tend to adapt to a certain current level. This means that if the current increase is too gradual muscle tissue will adapt to it, and the current will not elicit any contraction. Therefore the change of current will have to be sudden.

The type of current that reflects the characteristics just listed is a rectangular waveform, for which the current increase is practically instantaneous, which also has the following advantages:

*      Limited polarization effect
*      Limited nervous fiber adptation
*      Good recruiting of nervous fibers
*      Low current level

Excitation Mechanism and Necessary Impulse
To excite the nervous tissue the following conditions are necessary

*      Enough current through the targeted tissue
*      Adequate duration of the stimulus for the muscle group

Lapique’s law, shows the relationship between current intensity and duration, which also changes for different muscle groups.

Chronaxie and Rheobase
The relationship between current intensity and duration has been determined by Lapique. As duration increases, the current intensity necessary to trigger a contraction decreases.

Another characteristic of body tissue is that of accommodation, which means that any tissue gets used to a particular stimulus and consequently needs next time a stronger stimulus to trigger a reaction. Lapique defined two parameters as reference points to characterize and compare the effects of electrical stimuli: rheobase and chronaxie.

Rheobase is defined as the minimum current intensity necessary to trigger an excitation (action potential), no matter how long the duration of the stimulus is.

Chronaxie is defined as the duration necessary to trigger a reaction, when current intensity is twice the rheobase. This value is an excellent compromise to trigger a good contraction in a reasonably short time, without generating any accommodation, and without causing any of the negative side effects.

Chronaxie in Various Muscular Groups

Chronaxie is an important parameter for electrostimulation, because it determines the duration of each impulse. Therefore the duration of each impulse has to change depending on the muscular group. Generally there are 6 different areas to stimulate, with 6 different chronaxie values and therefore 6 different impulse durations; values may change from individual to individual. Average values are the following.
[ul]
[li]Lower Leg, 430 microseconds;
[/li][li]Upper Leg, 380 microseconds;
[/li][li]Lower Torso, 330 microseconds;
[/li][li]Upper Torso, 280 microseconds;
[/li][li]Arm, 200 microseconds;
[/li][li]Forearm, 230 microseconds.
[/li][/ul]

Characteristics of Waveforms Utilized by Electrostimulators
Modern e-stim machines utilize a biphasic, rectangular, symmetric waveform, which favor stimulation and keep a good comfort.

Biphasic Waveform
A biphasic current will transport ions first in one direction then it will reverse this direction. The alternated current will excite the tissue with the impulse that first goes in one direction, and at the same time it will minimize the net movement of ions, thus avoiding chemical burns and other irritations.

The Waveform
Body tissue tends to accommodate to stimulation that is gradual, and elevate the threshold potential. However, is not capable of doing so if this will not happen if the stimulus is sudden. Comfort will also be greater.

The chronaxie has to be adequate too. The waveform that better responds to these characteristics is rectangular.

15

Fibers and Stimulation Frequencies

Classification of Muscular Fibers
Voluntary muscles are formed by muscle fibers, all of which can shorten on command, contributing to a muscle contraction. However, they may have different characteristics, and they have been classified accordingly into:

[ul]
[li]Slow twitch, or slow fibers of type “I”
[/li][li]Fast twitch, or fast fibers of type “II”, which can be subdivided in
[/li][li]Fast twitch, or intermediate fibers of type “IIa”
[/li][li]Fast twitch, or very fast fibers of type “IIx” (formerly “IIb”); what used to be called IIb is called IIx by more recent research, and is the accepted correct denomination.
[/li][/ul]

The following link shows a Table of Fiber Properties. It can be understood from it that, depending on the goal, it’s useful to train certain types of fiber. For instance for endurance goals it is useful to train slow fibers. To increase maximum force it’ll be useful to train Type IIx fibers; it will not be useful to train type I fibers which are not capable to develop a high level of force. To correctly organize an electrostimulation session, it will be useful to select the type of program in line with the goals listed by this table.

Twitch and Tetany
To understand EMS contraction it is important to distinguish between muscle twitch and muscle tetany. When we apply a current stimulus the muscle contracts for a short period of time: this is called a twitch, the force developed is not very strong and lasts for a short period of time. After this the muscle becomes insensitive to the stimulation (it accommodates) and relaxes. However, if we apply several current stimuli in a short period of time, each twitch builds upon the peak of the previous twitch, and the strength of the contraction grows to a significant amount: this is called tetany, or tetanic contraction, and it is the basis of EMS.

The frequency at which the stimuli start building on top of each other, resulting into tetany, depends on the characteristic of the muscle fibers according to the table above. For example, slow-twitch fibers contract more slowly than fast-twitch fibers, their peak force taking place at a later time than in fast-twitch fibers. Therefore the next impulse does not need to take place as quickly as in a fast-twitch fiber, to build up into tetany. Therefore to cause strong training contraction in different fiber types we’ll need to employ different EMS frequencies, depending on the muscle fiber we want to train, and on the training effect that we want to obtain.

Stimulation Frequencies
The choice of stimulation frequency is very important for several reasons:
[ul]
[li]Different fiber types respond differently to different stimulation frequencies. A particular frequency will stimulate more fully fibers of a particular type.
[/li][li]The proportion of each type of muscle fiber “I”, “IIa” and “IIx” present in each muscle varies, depending on the function of the muscle.
[/li][li]The use of a particular stimulation frequency will tweak the muscle fibers of one type to adapt and work similarly to muscle fibers of another type that work well at that frequency.
[/li][/ul]
Therefore stimulation frequency is selective for the type of training that we want to obtain. It is measured in Hz, which means the number of stimulation impulses sent to the muscle in one second.

The frequency ranges to recruit prevalently different muscle fiber types are as follows.
[ul]
[li]1 Hz. 15 Hz.
[/li][li]15 Hz. 20 Hz.
[/li][li]20 Hz. 50 Hz.
[/li][li]50 Hz. 90 Hz.
[/li][li]90 Hz. 120 Hz.
[/li][/ul]

Stimulation between 1Hz and 15 Hz
At these low frequencies there isn’t a real contraction but only a series of twitches. The force developed by each muscle fiber at each twitch is slight, approximately 1/3 of what can be developed with a full contraction by the same fiber. As the frequency increases the twitches start to overlap.

Stimulation between 15 Hz and 20 Hz
As the frequency increases the twitches overlap ever more fully, and somewhere between 15 Hz and 20 Hz they become one strong contraction, the so called tetanic contraction. Stronger athletes will experience the tetanic contraction at slightly higher frequency.

Stimulation between 20 Hz and 50 Hz
Stimulation between 20 Hz and 50 Hz causes full contraction of slow fibers of type “I” which therefore are trained. With this selection it is possible to improve fatigue resistance, i.e. endurance characteristics, of these fibers.

Stimulation between 50Hz and 90 Hz
Stimulating between 50 Hz and 90 Hz, it is possible to work on intermediate fibers of type “IIa”, which have intermediate characteristics between slow type “I” fibers and fast type “IIx” fibers. This training will improve strength and a moderately help fatigue resistance.

Stimulation between 90Hz and 120 Hz
Stimulating between 90 Hz and 120 Hz, muscle fibers of type “IIx” will be trained with strength and speed characteristics, but scarce fatigue resistance.

Stimulation of Slow fibers - slow-twitch type “I”
To train these fibers one has to utilize frequencies between 20 Hz and 50 Hz.

Stimulation of fast fibers – fast-twitch type “II a”
To train these fibers one has to utilize frequencies between 50 Hz and 90 Hz.

Stimulation of fast fibers – fast-twitch type “II x”
To train these fibers one has to utilize frequencies between 90 Hz and 120 Hz.

Plasticity of Muscle Fiber Types
Earlier fiber-type research indicated that muscle fiber composition is very much genetically determined (i.e. the percentage of the various muscle fiber types in a certain athlete will not change with training). However, very recent research has shown that muscles trained with EMS exhibit a significant plasticity, depending on the frequency employed.

For a comprehensive explanation of muscle plasticity, see Vrbova, Hudlicka, Schaefer-Centofanti, Application of Muscle/Nerve Stimulation in Health and Disease, Springer 2008. For a study on plasticity relating to endurance athletes, see Nuhr et al., Functional and biochemical properties of chronically stimulated human skeletal muscle, 2003 European Journal of Applied Physiology. For a study on plasticity relating to force training, see Maffiuletti et al., Neuromuscular Adaptations to Electrostimulation Resistance Training, 2006 American Journal of Physical Medicine & Rehabilitation.

16

Electrode Placement

The electrodes have to be positioned to allow to the electrical impulse to arrive to the neuromuscular plate, which will then deliver the signal to contract to the muscle. To do this they have to:[ul]
[li]Be positioned entirely on the muscle;
[/li][li]Be aligned with the muscle fibers;
[/li][li]The negative electrode has to be close to the muscle origin;
[/li][li]The positive electrode has to be positioned at the center of the muscle mass
[/li][li]The negative electrode has to be twice the size of the positive electrode, if possible.
[/li][/ul]
Because we are utilizing a rectangular symmetrical waveform, it doesn’t make sense to distinguish between a positive and a negative electrode: both electrodes will be both positive and negative, depending on the instant considered. However, it’s a useful convention to discuss electrodes’ relative sizes.

It’s useful to have a smaller positive electrode, to concentrate the current to get deeper in to the muscle structure. However, since concentration of current more easily stimulates pain receptors, in some cases a larger pad will allow the individual to obtain a stronger stimulation below the pain threshold.

When to utilize two electrode pads of the same size
Some muscle groups are stimulated with electrodes of the same dimension for ease of use. This is the case of muscles of smaller dimensions, like the biceps.

How to position electrode pads on a muscular group
To position the electrodes correctly on a muscular group, the negative electrode is positioned proximally (i.e. closer to the vertical spine from which all nerves irradiate). Then the positive electrode is positioned on the center of the muscle belly.

Verify the correct position
Before starting the real stimulation training, verify the correct position of the electrodes, with a warm up program, i.e. lower intensity and reduced parameters. It’s useful to have a muscle anatomy chart handy, to help with electrode positioning.

Commercially Available Electrode Pads
On the market there are electrodes made with different materials for different uses. Most are for for muscle stimulation, but there also pads for pain therapy (TENS) made out of different plastic material.

Plastic Electrode Pads
Plastic electrode pads also known as gel, are made of a conducting plastic material. They are flexible, and need gel to be spread on the surface to improve conductivity and eliminate areas where the current would concentrate.

This type of pads also need a means to keep them in place. Medical tape is suggested rather than an elastic band, to avoid blood vessel constriction. They are recommended when there is a lot of hair or if the electrostimulation training is combined with movements.

Self-Adhesive Electrode Pads
Self –adhesive electrodes are made of a conductive mesh end of a conductive layer that acts both as a gel and as the adhesive. The gel improves conduction eliminating irregularities of the skin as a conduction obstacle. It’s easy to use, even though adhesiveness deteriorates with the number of uses, especially in presence of sweat. Duration varies a lot also depending on the quality of the pad. Skin lotions are detrimental to adhesiveness and duration.

Self-Sticking Film
Another recent product is a solid gel film that can be used jointly with plastic pads, to replace only the adhesive part, when this wear out.

17

The Training Session
To obtain good training results, it’s important to select the correct program. This means first of all the stimulation frequency to pursue the training goals intended. Once selected the stimulation protocol, it’s important to plan the training session in detail. The principles are the same as in a traditional training session.

Integrating Stimulation with Traditional Methods
It is important to consider that electrostimulation training contracts muscle fibers without the intervention of the Central Nervous System (CNS). Later on the CNS will have to reap the benefits of electrostimulation training without electrostimulation itself.

Therefore electrostimulation cannot replace traditional training, but has to be integrated with the other methods. It’s therefore very important to plan and schedule correctly the various activities. With a correct integration of the various methods, both muscular properties and functional properties will improve together.

The Training Session
Before starting an electrostimulation session it is recommended to warm up.

Warm-Up
A warm up prepares the muscles to completely receive the benefits of the stimulation, and to limit delayed onset of muscle soreness (the day after soreness). In addition the muscle uses up energy and the rest of the body needs to get ready to the change.

Systemic Warm-Up
For an adequate electrostimulation training session, especially if demanding, both muscles and cardiovascular system have to be activated to start them toward an intense training for the muscle fibers. For cardiovascular activity, a bike, a step machine or a treadmill can be utilized for 8’ – 10’ minutes.

The warm up of the whole system is important especially for large muscle groups like quadriceps, calves, gluteus, abdominals or pectorals.

Specific Warm-Up
Although a systemic warm-up can be skipped, if the stimulation doesn’t require a big muscular commitment, or if the muscles are small, a specific warm up is always recommended. The choice of training warm-up is extremely dependent on the muscular group that has to be stimulated, and on the individual. Quadriceps, biceps, abdominals, pectorals and dorsals can for instance all be warmed up. During warm-up the muscles should not be fatigued nor stressed, but just prepared to be ready to capture the advantages of an electrostimulation session.

Electrostimulation Warm-Up
Once the physical warm up is completed, the electrode pads will be positioned on the muscles to be stimulated. The chronaxie utilized has to be the correct one for the muscular group to be trained. Warm up programs do not need to fully contract the muscle as in a training program. Modern electrostimulation programs are normally supplied with a range of stimulation frequencies that cover all needs.

Amyotrophic Warm-Up
In case of stimulation of amyotrophic and hypotonic muscles, the programs to be utilized will have not to stress the musculature. A program of this type will have a frequency between 5 Hz and 10 Hz, will not cause a tetanic contraction, and will stimulate continuously without pauses.

Force Warm-Up
For warm up before strength programs, it may be convenient to use a more demanding warm up, with tetany of the muscle, but without fatiguing the muscle. Slow fibers of type “I”, stimulated between 20 and 35 Hz, will effectively increase blood flow to the muscle to be warmed up. Current intensity has to be high enough to cause a contraction, but has to stay low so that the muscle does not get fatigued. Contraction has to be alternated with rest to avoid contraction pains or cramps.

18

The Training Session (continued) - Work
After warm up, the muscle is in the best condition to train. The program has to be selected as a function of the result that has to be obtained, with frequency targeting the fiber types that have to be trained.

Know the Stimulation Objectives
Analyze what the needs of the athlete are, as a function of the sport, or of the functional athletic gaps that the individual has.

Define the Muscular Characteristics to Train
Define what muscular qualities have to be trained.

Know the Relationship between Muscular Characteristics and the Muscle Fibers to Stimulate
As a function of the muscle qualities that have to be improved, decide if they are slow-twitch fibers type “I”or intermediate fast-twitch fibers of type “IIa” or fast-twitch fibers of type “IIx”.

Chose the Stimulation Frequency
Pick a frequency as a function of the objectives to be pursued.
Choice of the Stimulation Frequency
Once decided which muscle fiber types have to be stimulated, chose the stimulation frequency that best recruits the fibers. The following list gives a good indication
[ul]
[li]20 Hz 50 Hz Slow fibers of type “I”
[/li][li]50 Hz 90 Hz Intermediate fibers of type “IIa”
[/li][li]90 Hz 120 Hz Fast fibers of type “IIx”
[/li][/ul]

Work Positions and Methods
The position to assume during stimulation must have the following characteristics:
[ul]
[li]Most comfortable;
[/li][li]Must give the least joint problems;
[/li][li]Must allow the highest stimulation intensity;
[/li][li]Contracts the muscle in a way similar to that of the sport event.
[/li][/ul]
It must be decided whether to further load the muscle, with voluntary contraction and with or without loads.

Electrostimulation Alone
Electrostimulation alone is effective only for functional recovery, but is extremely limiting for training purposes.
To utilize electrostimulation at intensities adequate for training it is important to limit the movement of the part of the body to which the muscle is attached. This has to be avoided because it could cause either muscular or joint pain. This is easily solved by using fixed resistance.

Combined Methods
By combining training methods, electrical stimulation increment its ability to train the individual. Not only artificial loads but just natural are enough to obtain this result. In addition stimulation comfort increases and the athlete is therefore able to use higher stimulation intensities, which favor a better recruiting.

Natural Loading
It is useful and practical to stimulate the muscle during a training session, utilizing only the weight of the body, because it can be done anywhere. It is also the base stimulation training adopted by trainers, and it is useful for competing athletes who are continuously traveling to competitions.

However, it may not be the best training session. Not all muscular groups are well suited to natural loading. All extending muscles of the the legs can be trained well with stimulation and natural loads because of their natural way of working against gravity during a concentric action. Abdominal muscles too, can be stimulated without overloads, limiting the range of motion of the joint.

However, it is difficult to utilize this working method on muscular groups that normally do not work against gravity. For instance the biceps brachii, or the flexing muscles of the leg (like the hamstring or the calf).

Additional Loads
Utilizing overloads and electrostimulation together, resolve many of the problems of electrostimulation either alone, or with natural loads. In fact the presence of an overload reduces the risk that the stimulated muscle shortens too much with pain and possible risk of cramps.

By using additional loads, it’s also possible to train an individual affected by muscle, tendon or joint pathologies. This can be done by selecting and fine tuning the method that works best, avoiding at the same time to worsen the pathology. Gym machines in addition can limit the range of motion during the exercise.

19

The Training Session (continued) - Muscle Groups - the Rest of the Session
Quadriceps
Extensory muscles of the lower limbs are the most trained. To train the quadriceps it’s possible to utilize with stimulation a series of exercises with overloads, like the leg extension or leg-press. All of these exercises are good to increase strength, depending also on the stimulation frequency used during the session.

Biceps Brachii
To stimulate the biceps it’s best to use the electrostimulator with free weights or on a bench.

Leg Flexor
To stimulate the leg flexors, the most convenient solution is to use a leg-curl machine.

Abdominals
Abdominals are best stimulated without performing a crunch exercise or without any overload. Stimulation solely with the natural load gives best results, both for muscular tone and strength, without overloading the back. This limits muscle aches or joint problems on the vertebrae.

Recommendations
[ul][li]When performing dynamic exercises, either with natural load or with overload, it is recommended to be with a person expert in the training method to avoid problems. It’s safer also to use electrostimulation with ROM (range of motion) machines to keep the motion within a safe range. The muscle shall never be stimulated when in its shortest position, to avoid contractures and pain.
[/li][li]Defatigueing. After stimulation it’s useful to spend 5’ or 10’ minutes defatigueing the muscle. The most effective recovery is not just rest, but a bland activity defined as Active Recovery in which the muscles are stimulated at a frequency between 1 Hz and 10 Hz, and must be performed in a position in which the muscle can be relaxed and almost completely at rest.
[/li][li]Transformation. Once the stimulation session is over, it’s useful to add some dynamic voluntary exercises which increase the effectiveness of the stimulation. This phase, called transformation, has the athlete select the exercises and work methods most useful to reach the training objectives. For this it is important to know whether one wants to act on strength or if one wants to have a lighter end of the training and work on coordination.
[/li][li]Force. If one wants to complete the training by working on strength development, one has to utilize overloads, managed with specific methods as a function of short, medium and long term objectives desired.
[/li][li]Coordination. If one wants to improve the sport technique, it is convenient to utilize reduced or no overloads, and concentrate on precision and speed of movement, exploiting the muscle fatigue induced by stimulation. In this way it is possible to make the athlete repeat competition movements, but in more difficult muscle conditions. For a high level of coordination, after stimulation a technical training could follow, even though with moderate intensity.
[/li][/ul]
Stimulation Duration
The best duration for a stimulation session cannot be standardized, even though a range of duration can be considered for the most typical needs.[ul]
[li]Warm-Up. Electrostimulation warm-up is generally done with a duration of 5’ minutes, both for a session of functional recovery and for a toning session for aesthetics.
[/li][li]Work Phase. The real section of the stimulation session (i.e. after warm-up), can last even just 10’ or 15’ minutes, if the individual is not yet used to this training method, and his/her musculature is hypotonic (weak) and hypotrophic (underdeveloped). Training sessions for individuals who are already used to stimulation can last even 40’ or 50’ minutes, obviously with programs tailored to the need and the type of session wanted. General prescriptions cannot be done, and it’s best to adapt the general concept to the needs of the individual to train.
[/li][li]Defatigueing. Defatiguing or active recovery is useful if it lasts for at least 5’ minutes, but could last much longer depending on the degree of fatigue of the individual being stimulated.
[/li][/ul]

20

Programming
The market for electrostimulators has opened to devices that within consumer reach can offer good performance to professionals. Programmable stimulators allow coaches, strength-and-conditioning trainers and athletes to customize stimulation programs by adjusting the electrical parameters. Customization, if done correctly by knowledgeable people, adapts stimulation training exactly to the need of a particular athlete. It takes advantage of the physical characteristics of the individual and adapts them to the goals of the sport targeted.

In other words customization produces better results. The converse is true. Incorrect programming not only is not going to give the hoped for results, but it may be detrimental to the goals.

The Best Choice
Although commercially available devices allow one to program training sessions, it is better to adjust electrical stimulation parameters with a professional who know how to proceed.

When to Program
Some stimulators allow for an adjustment of electrical parameters for total customization. This has to be done with caution. The departure from standard parameters has to be done with a complete understanding of their effectiveness, and the effects of change on the results of training.

The following questions will help:
[ul][li]What’s the stimulation objective?
[/li][li]Is it possible to reach the same goal by using one of the program offered as standard by the device?
[/li][li]Is it really necessary to customize the stimulation?
[/li][li]Am I able to make the best selection of stimulation parameters for the goals pursued?[/ul]
[/li]If after this analysis one decides to pursue programming, it is necessary to learn in depth the meaning of all the parameters.

Electrical Parameters and their Meaning
[ul][li]Type of current
[/li][li]Session duration
[/li][li]Chronaxie
[/li][li]Increase Ramp
[/li][li]Contraction Time
[/li][li]Decrease Ramp
[/li][li]Rest Time
[/li][li]Contraction Frequency
[/li][*]Rest Frequency[/ul]