EMS Theory

Expert Discussion Advanced Sports Sciences
21

Parameters and their meaning

Type of Current
The choice of the type of current is normally limited to either TENS or EMS. TENS (Transcutaneous Electro Neuro Stimulation), allows the programming of program with analgesic (pain therapy) effects. EMS (Electro Muscle Stimulation) supposedly is for strengthening goals. Russian programs (aka Kots currents) have several drawbacks, which will be explained in a later post, and have been entirely replaced by biphasic, rectangular, symmetrical waveforms (aka square wave); therefore when we talk of EMS we exclusively refer to the latter.

Treatment Duration
Session duration depends on the needs of the individual. Minimum or maximum duration cannot be prescribed. However, normal durations go from 30’ to 60’ minutes. Often it’s possible to combine together different programs that together determine the total duration.

Chronaxie
Chronaxie is the duration of the single impulse or waveform phase, and depends on the muscular group. Adjustment of this parameter may improve or worsen the stimulation effect and cannot be changed on a whim. It has to follow an indicative table of values depending on the muscle.

Different individuals may have different chronaxie values. The utilization of chronaxie values much higher than normal would stress the muscle without obtaining a training benefit. Chronaxie values below optimal stress less, but either the effectiveness of the training will be lower, or the athlete will have to increase the current to an uncomfortable level; in addition many fibers will not reach the stimulation threshold and some fibers will get into accommodation. Chronaxie lower than suggested may be used for individuals who are weak or recovering from muscle injury.

Muscular Contractions
The work phase is made of three different segments which affect both comfort and fatigue:[ul][li]Ramp Up
[/li][li]Contraction time
[/li][li]Ramp Down[/ul]
[/li]
Ramp Up
Ramp up is the time it takes to go from 0 to the current intensity wanted during the work portion. Too-short ramps do not give the athlete time to get ready to the contraction, and the sudden change will be uncomfortable. Too-long ramps will fatigue the muscle before it reaches the contraction needed for training. Most sport training programs ramp-up in 0.5” to 2” seconds.

Contraction Time
During contraction time muscle fibers will perform their training work. The muscle will use up energy. This is a delicate phase, because surpassing maximum resistance of the muscle fibers could cause contractures and cramps.

The duration of this phase doesn’t have a fixed standardized value, but must be evaluated as a function of the type of fiber. The figure in this link shows reference values. In general, contraction and rest times are not too different from values used for voluntary resistance or dynamic training. Remember that the muscles are physiologically contracted in the same way as for voluntary training: the same metabolic and adaptation mechanisms are still valid. If the individual whose advice you are following is knowledgeable about EMS, this person may have particular goals in mind that would differ from the examples given.

Ramp-Down
This parameter is less important than ramp-up for comfort. However, a too sudden decrease of contraction force may be unpleasant. If it is too long, it will contribute to fatigue.

Rest Phase
Rest time between contractions has to be long enough to allow catabolite flushing from the muscle fibers. A very low frequency between 1 Hz and 4 Hz will cause the muscle to pump blood through the fibers and facilitate flushing of the byproducts of contraction. Slow-twitch type “I” fibers do not need a rest time as long as fast-twitch type “IIx” fibers.

Frequency During Contraction
Stimulation frequency allows selecting the type of fiber being trained. It will be between 20 and 120 Hz depending on the fiber.

Frequency During Rest
Between two contractions it is necessary to have a short rest time to allow blood to refuel the muscle, and to take away waste products of the previous contraction. A low frequency that massages the muscle increases blood flow. During active recovery a frequency between 1 Hz and 6 Hz can be utilized.

Who Needs Customized Stimulation Parameters?
Standard programs found in professional electrostimulators on the market are good for most individual, and program customization should be done only when needed.

Are We Able to Program?
Knowing the meaning of electrical parameter is not enough to be able to program, and a lot of practical experience is necessary. The first step is to analyze the parameters of the programs already available. To gain an understanding of the protocols and to change them it is necessary to discuss them with an expert.

A Different Interpretation of Stimulation
Only a small group of athletes will need a modification of the electrical parameters. It is important instead to customize for the need of each athlete the protocol of the training program.

For instance the sequence of the programs and their duration will have to be modified obtaining a precise duration of the entire training session. In this way the goals of the athlete can be reached even though the electrical parameters are the same.

22

Russian Currents.
Russian currents encounter the sympathies of many practitioners, and many are still using them. The reasons are historical: Russian currents were the first to succeed at professional sport training. Although modern training currents have evolved toward square wave currents, old habits get entrenched and are culturally difficult to change, because they are transmitted from early users to newer users.

I will explain using the principles of EMS theory presented, why Russian stimulation works, how a square wave compares with it, and why the latter is more performing. I will interchangeably use the term Russian current, Russian program or Russian stimulation for the same protocol introduced by Russian scientist Yakov Kots. I will also interchangeably use the term rectangular current, square wave, or Biphasic Rectangular Symmetrical waveform for the electrostimulation current we have considered so far.

Back to Lapique’s law. We have seen that there is a direct relationship between current intensity and pulse width to excite a nerve cell. This is true for nerve cells innervating muscles, also known as motor neuron (measured in microseconds, that is millionth of a second, and for short μs). Keep in mind that we are exciting a motor neuron and not a muscle fiber. The motor neuron then triggers the muscle fiber in a physiologically-natural way.

With reference to the attached diagram, we can see that if we use a pulse width equal to the chronaxie of the muscle, we strike an intuitively sweet spot in the muscle: the intensity doesn’t need to be too high, and we don’t need to stimulate the muscle for too long.

With reference to the alternatives: square wave A excites the motor neuron for a shorter time, but requires percentage wise a much higher intensity; square wave B excites the motor neuron for a longer time, thus requiring lower intensity; the gain in lower intensity though has to be compensated percentage wise by a much longer stimulus which stresses the nerve cell. We are left with curve C which uses pulse width equal to chronaxie, the best compromise in terms of energy expensed to excite the nerve (an in turn the muscle it innervates). (Minimal energy expenditure can be demonstrated with high-school calculus starting from Lapique’s law I=Rheobase + Rehobase*Chronaxie/T). We utilize this chronaxie to generate the proper square wave attached.

Although Lapique’s law dates from the early 20th century, its full implications for training and measurement of parameters involved were not fully understood until much later. Many researchers were therefore experimenting with a wide range of many parameters: different waveforms, different frequencies, different pulse widths, different current intensities, as well as on/off times, duration of the training, repetitions, sessions per week etc. One can understand that to try all the possible combinations, and having to wait a few weeks for each experiment, to measure results, would take too long. Science advances by both understanding of the phenomenon, intuition of possible implications, and trial and error. Then somebody has a better intuition, or hits a lucky attempt. The better results obtained are studied, more light is shed on why it works, and from the new knowledge more experiments are tried to advance even further.

This is what happened to Russian scientist Yakov Kots: guided by profound understanding, and experimenting with various combinations of parameters that made sense to him, in the ‘60s he started hitting on a combination that produced results. You have to remember than in the 60’s solid-state electronic was at the beginning and miniaturization was not available (it was just being invented to put a man on the moon with NASA’s Apollo program). It was far simpler for a researcher to generate an electric pulse with readily available electronic tubes rather than to experiment with transistors. Therefore the waveforms that Kots had at his disposal were so called sine-wave pulses as in this picture. Experimenting with various frequencies, he refined his results and consolidated the findings in a training current at 2500 Hz, on for 10 ms (milliseconds) and of for 10 ms (see attached).

Let’s take a look at a single 2500-Hz sine wave. Looking at its shape one can see that 2500 Hz translates into one full wave every 400 μs: 2500 Hz means that the wave repeats itself 2500 times every second, therefore 1/2500 = 0.0004 s = 0.4 ms = 400 μs. That also means that the positive half of the sine-wave pulse, which triggers the motor neuron, concludes itself within 200 μs.

Let’s superimpose it on a square wave, and look at the area under the waveform (attached curve), which roughly correlates with the excitation: the sine wave will have to rise much higher to excite the motor neuron. If you look at the area enclosed under the Russian wave, you can easily see why to get the same excitation, the peak of the Russian has to be turned to much higher intensity (i.e. more uncomfortable or painful) than a square wave to obtain the same excitation.

In other words a square wave gets more bang for the buck than a sine wave. However, sine wave was the best technology available at the time, and electronic was not sophisticated enough to produce a good square wave.

Another comparison factor is that Russian stimulation is fixed, whereas square wave stimulation is more flexible. We have seen in previous sections explaining the theory of EMS, that the chronaxie of different muscle group may vary between 200 μs and 450 μs. Russian stimulation has always the characteristics of approximating 200 μs pulse width duration. This value is just too low for certain muscle groups like the legs, whereas the pulse width of a square wave can be changed at leisure, adapting it to the muscle group.

The last parameter of Russian current to understand is its on/off time of 10 ms. For Kots, it was presumably easy to interrupt his 2500 Hz sine wave every 10 ms, because in Europe AC current from an outlet is available at 50 Hz, and this was used as the triggering signal to turn it on and off. Thus Kots obtained a train of sine-wave pulses at 50 Hz as shown in the attached picture. The sequence of pulses is called a pulse train; you can fit 25 of these sine waves within the first 10 ms of the Russian wave; then there is an interval of another 10 ms during which there is no current, and the whole sequence restarts: all this takes place in 20 ms, which results in the 50 Hz frequency. Thus it is directly comparable to a square wave at 50 Hz and pulse width 200 μs.

But what happens after the first sine wave in the Russian train of pulses excites the motor neuron? There is another physiological phenomenon called refractory time, according to which, once a neuron has been excited, it’s impossible to excite it again until some time later. Refractory time lasts a few milliseconds, which renders the next few sine pulses of the Russian pulse train useless. This is one more reason why Russian currents are not as effective: much of the energy injected in the motor neuron goes wasted.

To summarize, Russian currents compared to square wave currents have the following shortcomings:[ul][li]Require much higher current intensity, which is much less comfortable;[]Do not offer pulse width flexibility for different muscle groups;[]Do not offer different frequencies for different stimulation goals;[*]Waste a lot of unneeded energy in the muscle tissue, triggering several possible issues,
[/li]skin irritation,
tissue heating,
shorter battery lifespan.
[/ul]

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ANATOMY AND ELECTRODE PAD PLACEMENT
Practical examples and videos of pad placement can be found at
www.globuscorporation.com/eng/catalogo.asp?cat=0&idcat=1&sottocat=3&idsottocat=39. Pictures for the muscle groups discussed below can be seen by clicking on the Pad Placement link for each.

FEMORAL QUADRICEPS
The quadriceps is the main extending muscle of the lower leg with respect to the upper leg. Its various sections start from the hip and femur, and converge on one common tendon attached to the tibia. It also elevates the thigh with respect to the hip. It contrasts gravity, keeping an individual standing. It’s of utmost importance in all sports using the legs, from running to jumping, biking etc.

When to train it
Given it’s function to contrast gravity, it’s important in all sports in which the trunk has to be moved vertically: volleyball, basketball, high jump, long jump, soccer, football, rugby, skiing, gymnastic.
It’s equally important in running sports in which explosive force or resistance of the quadriceps are needed. The type of stimulation program needed depends then on the sport, and the choice of frequency is consequential.

Pad Placement
The electrode pads can be positioned in a few different manners, depending on the goal. The most simple is:
[ul][li]Inactive (Negative) Electrode: centrally in position close the hip so as to be on top of vastus medialis, vastus lateralis, and rectus femoris.
[/li][li]Active (Positive) Electrode: on the muscle belly of the vastus medialis, at its center;
[/li][li]on the muscle belly of the vastus lateralis at its center.
[/li][/ul]

To be continued by next muscle group: Gastrocnemius.

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GASTROCNEMIUS calf
Similarly to what said for the Quadriceps, the extensory musculature of the lower leg has an important role counteracting gravity. It is very important for all running and jumping activities. The origin of the muscle group is on the femur, and the soleus on the tibia, converging on achille’s heel attached to the calcaneous bone. This muscular group gets activated together with the quadriceps and the gluteus. Because the quadriceps is larger, individuals have a tendency to underestimate its importance in dynamic situations, and in training.

When to train it
When power and explosive force are needed. For example in volleyball, basketball, and other athletic disciplines with similar motor demands. It is of utmost importance in all disciplines like fast running and and middle distance running, in which the movement of the ankle is important. In downhill skiing it is used very much. In cycling it is also very important both in its static and endurance action.

Pad placement
[ul]
[li]Passive electrode: position the pad at its beginning, totally placed on the muscle; do not place it too close to the cavus popliteus, which could impair the movement of the knee.
[/li][li]Active electrodes (two): they must be placed distally, at the center of both muscle bellies that make the gastocnemius.
[/li][/ul]

To be continued by next muscle group: Gluteus.

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GLUTEUS MAXIMUS
It is considered the third and last of the extensor apparatus of the the lower limbs. Its origin is in the ridge going from the ilius to the sacrum and coxis, and its insertion is on the femur. It’s mainly responsible to maintain an erect position, since it abducts the thigh with respect to the trunk. Therefore with the quadriceps and the calf is responsible to counteract gravity. It is thus important in training finalized to running and jumps.

When to train it
It can be trained for all the situations already considered for quadriceps and calf. Because of its anatomical position it is particularly important in extensions starting from a position in which the angle between trunk and leg is small. Training of the gluteus is particularly important in sports like skiing and carving. In general the gluteus is important in all sports that require explosive strength and power to be developed by the lower limbs. Therefore volleyball, basketball, soccer, ski, athletic, skating etc. will benefit from its training.

Pad placement
[ul]
[li]Inactive electrode: In proximity of the great trochanter, slightly higher and closer to the center line, and perpendicular to the direction of the gluteus maximus fibers.[/li][li]Active electrode: At the center of the muscle. Some trainers prefer a smaller electrode for stimulation of deeper muscle fibers (it’s debatable).[/li][/ul]

GLUTEUS Medius and Minimus
The small and middle gluteus participate to the extensory movements of the lower limbs, specifically in the outward rotation and abduction of the thigh. These muscles are deeper than the gluteus maximus. They originate just below the crest of the ilium, and have their insertion on the great trochanter (protuberance) of the femur.

When to train it
To be effective the stimulation of these muscles has to be done with that of the gluteus maximus. It is mostly doen to obtain aesthetic results. From a sport point of view it does not give particular advantages over a stimulation of the gluteus maximus only.

Pad placement
[ul]
[li]Inactive electrode: Close to the great trochanter, parallel to the gluteus rim, slightly on the internal side.[/li][li]Active electrode: At the center of gluteus. The picture’s top two pads (blue connectors) are for the Gluteus Medius. However, it may be preferable to use larger pads (4" long) in a slightly higher position.[/li][/ul]
To be continued by next muscle group: Hamstrings.

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HAMSTRINGS
In the back of the thigh there are three muscles that flex the lower leg on the upper leg: biceps femori, semitendinosus and semimembranosus. They originate at the ischium and insert at the Condyle of the tibia and the head of the fibula. They flex the lower leg on the upper leg, and in a limited way in collaboration with the gluteus they help the extension of the leg from the trunk. The flexing muscle controls the knee joint in antagonism with the quadriceps. A good equilibrium between flexor and extensor muscles of the leg will help prevent problems on the knee.

When to train them
It’s rare to have to train the hamstring muscles selectively, because it’s rarely in deficit with respect to to the other extensors muscles. It could be useful to train the flexory muscles in those sports, like soccer, skiing and crosscountry skiing, in which it is important to train the extension of the thigh on the trunk. It is also useful to train these muscles when the risk of knee and ACL traumas is high.

Note
When stimulating the flexor muscles it is important to look after a balance between these muscles and the extensors muscles, because an imbalance would cause instability of the knee.

Pad placement
It is convenient to utilize only two large electrodes, because of the anatomy of the back of the thigh.
[ul]
[li]Passive electrode: t the center of the thigh just below the gluteus
[/li][li]Active electrode: At the level of the third distal , in the center of the belly of the muscle.
[/li][/ul]
To be continued by next muscle group: Abdominals.

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RECTUS ABDOMINIS

Two electrodes pad placement.

The rectus abdominis is a long and thick muscular ribbon, interrupted by connective tissue strips; it originates from the pubic crest and inserts into the last ribs. In its respiratory function lowers the ribs, and in its dynamic function flexes the spinal column forward. The rectus abdominis, conjointly with the transverse abdominis, and the obliques stabilizes the spinal column giving solidity to the trunk. Because of this stabilization function it has an important role in almost all dynamic movements, and it maintains the posture.

When to train it
Among all muscles that can be trained with an electrostimulator, the rectus abdominis is the winner. Because of its role in stabilizing the spinal column and the hips, it is important in all sports in which it has to develop either force or speed of the lower limbs. Its tone is also important in all sports that use the arms, which need a good supporting base. Therefore any sport benefits from a selective training of the abdominals.

Pad placement
It’s possible to utilize four large electrodes (or two, each across the abdominal wall), but there are also other possibilities.[ul]
[li]Inactive electrode: between the iliac crests and the navel.[/li][li]Active electrode: at the level of the rib arc such that the electrode stay on the abdomen and not on the ribs, to avoid that the stimulation act on the intercostal muscles.[/li][/ul]

RECTUS ABDOMINIS – Six Electrode Pads
To stimulates the abdominals, instead than 2 large electrodes one can also use 2 large electrodes and 4 small. Six electrodes allow to optimize the location of the stimulation and to utilize more channels. The two arrangements give the same results, and only depend on preference.

Pad placement

The two large pads are the passive electrodes, and are placed in the same location as for the 2-electrode arrangement, but more apart from each other.[ul]
[li]Passive electrode (lower): at the iliac crest, between the navel and the pubic area in the center.[*]Passive electrode (upper): At about the rib arc, above the navel, such that the electrode remains completely on the abdomen, to avoid inter-costal muscle stimulation.[/li][li]Active electrode: Around the navel, two above, in the area included between the upper passive pad and the navel; two in the area between the lower passive electrode and the navel.[/ul][/li]
TRAVERSUS ABDOMINALIS – two pads
Origin laterally from the last two ribs. It’s perpendicular to the other abdominals and it stabilizes the spinal column without participating much to dynamic movements.

When to train it
It’s important in sports in which both lower and upper limbs are used. It helps protect the spinal column. It can be stimulated for aesthetic goals.

Pad placement
Similarly to what said for for the other abdominals, there are different arrangements to position the electrodes, the simplest being with two large pads. Active and passive electrodes are completely interchangeable.With reference to the picture for six pads, only the two outer pads are employed (if using double input pads, connect only one input to each terminal of the same channel).
[ul]
[li]Passive electrode: laterally with respect to the abdomen, but below the ribs so that the intra-costal muscles are not activated.[/li][li]Active Electrode: at the opposite side of the passive electrode with respect to the abdomen.[/ul][/li]
TRAVERSUS ABDOMINALIS – six pads
With two large and four small electrode pads. Use either arrangement depending how the athlete is responding to the stimulation.

When to train it
This arrangement is used especially for aesthetic reasons. Because this muscle contains the abdomen, its toning favors a better look, but it doesn’t help with losing fat layers.

Pad placement
[ul]
[li]Inactive electrode (right): vertical position in proximity of the point where the ribs are almost parallel to the iliac crest. Do not position on the ribs, to avoid contractions of the inter costal muscles.[/li][li]Inactive electrode (left): on the opposite side of the abdomen.[/li][li]Active electrodes: the four small electrodes are in proximity of the navel, parallel to the inactive electrodes.[/li][/ul]
To be continued by next muscle group: Trapezius.

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TRAPEZIUS
The trapezius has a very wide origin on the spine, and inserts on the clavicle and scapula. It’s divided in three main sections, with different functions. The upper fibers, starting from the cervical vertebrae, elevate the scapula and rotate it outward. The middle fibers originating from the dorsal vertebrae adduct the scapula toward the spinal column. The lower fibers lower the scapula rotating it inward. Overall it stabilizes and controls the scapula, which is important in sports that utilize the arms to throw or to lift the body.

When to train it
Electro stimulation of this muscle has to be combined with training of the other muscles that participate to the movement. It can be useful in climbing, tennis, volleyball, swimming.

Pad placement
The electrodes have to be placed depending on which section of the trapezius needs to be trained. Placement for the middle section follows.[ul]
[li]Inactive electrode: the large pad must be positioned at the third medial of the scapula, with the long side parallel to the spinal column.
[/li][li]Active electrode: Two small electrodes are placed in proximity of the spinal column, approximately one inch from the spinous processes, and parallel to the inactive electrode.
[/li][li]The upper pad at the same height of the large pad, and the second small pad a little lower.
[/li][/ul]
To be continued by next muscle group: arm muscles.

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BICEPS BRACHII
The biceps is made of a long and a shorter head, originating from the scapula and humerus and insertion in the radius. The main function is to flex the forearm on the arm, and helps to elevate the arm, or to lift the trunk (climbing).

When to train it
Stimulation is recommended for climbers, for rowing, swimming, tennis and all sports using the upper limbs.

Pad placement
Positioning is simple. It’s possible to use two small electrodes or one large/ one small compatibly with the absolute size of the muscle.
[ul]
[li]Inactive electrode: positioned just before the deltoid covers the biceps, aligned at the armpit.
[/li][li]Active electrode: on the muscle belly of the muscle; just flex the muscle, it’s the point where the muscle bulges the most.
[/li][/ul]

TRICEPS BRACHII
Origin with three tendons: from the infraglenoid tubercule of the scapula, and above and below the radial groove of the humerus; all three inserts into the ulna. It extends the forearm with respect to the arm, and it’s the antagonist of the bicep.

When to train it
It’s useful to stimulate this muscle to train throw and push of the upper limbs. Main sports that benefit from it are volleyball, crosscountry skiing and all disciplines in which it is necessary to throw an object. It is also trained for aesthetic reasons.

Pad placement
Positioning is not difficult, depending on the individual (only one channel has been connected in the picture, the other one is similarly connected)
[ul]
[li]Inactive electrode: on the posterior face of the arm at the height of the armpit where the triceps can be felt, that is below the lower margin of the deltoid.
[/li][li]Active electrode: because the are two muscle bellies, it is necessary to place one active electrode for each. These can be determined with a voluntary muscular contraction
[/li][/ul]
To be continued by next muscle group: Pecs & Shoulder.

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PECTORALIS MAJOR
The pectoralis major originates from the clavicule, from the sternum and from the costal rib cartilage; the three origins converge on the insertion on the humerus. It adducts and rotates inward the arm; if the latter is kept fix, it helps elevating the trunk. It also helps deep inspiration.

When to train it
The pectoralis covers a main role in all athletic-throw sports, and intervenes during play in volleyball, tennis. It stabilizes the dynamic movement of the shoulder. It is also important in climbing, swimming and wind-surf. Because of these multiple functions its training is recommended in any sport utilizing the upper limbs.

Pad placement
Electrode positioning is finalized to the functionality of this muscle during execution of a movement.
[ul]
[li]Inactive electrode: use a large rectangular pad, placed proximally to the armpit, just before the point where the pectoralis buries under the deltoid.
[/li][li]Active electrode: both acive electrodes are placed at the center of the muscular mass of the pactoralis. The lower pad is placed above the nipple, slightly toward the sternum. The upper pad is positioned above the latter, and closer to the sternum.
[/li][/ul]

DELTOID
The deltoid is made of three sections, anterior, lateral and posterior. The anterior section originates from the clavicle, the lateral originates from the acromion, and the posterior from the scapula. All three sections insert in the humerus, but because of their orientation they are functionally different.
[ul]
[li]The anterior moves the arm forward, rotating it inward.
[/li][li]The lateral abducts laterally and lifts the arm.
[/li][li]The posterior moves the arm backwards in extension.
[/li][/ul]It stabilizes all shoulder movements, collaborating with deeper muscles.

When to train it
Because of its stabilization effect, this muscle should be trained for all sports that considerably load the upper limbs. In throwing sports there is also a collaborative effect. It is therefore useful to train in for volleyball, basketball, swimming, ski, carving, throwing sports, canoeing, kayaking and climbing.

Pad placement
Correct positioning of the electrodes on the deltoid takes into consideration the three sections. It is therefore convenient to use a rectangular inactive electrode, and two active smaller electrode pads on the anterior and posterior sections. It is not convenient to place electrodes above the shoulder to avoid bothersome compression feelings on the shoulder joint.
[ul]
[li]Active electrode: positioned on the humerus, just above the insertion of the deltoid on the humerus; this place is recognizable by the fact that the muscle tends to reduce its width.
[/li][li]Inactive anterior electrode: on the belly of the anterior section of the shoulder.
[/li][li]Inactive posterior electrode: the posterior inactive electrode is placed similarly on the belly of the posterior section of the muscle
[/li][/ul]

LATISSIMUS DORSI
The Latissimus Dorsi originates from the spinal column (L1-5, T7-12), the posterior ribs, the ilium and the sacrum; it inserts into the humerus. Its function depends on what is kept fixed: it rotates inwards, moves back and adducts the arm; or it elevates the trunk.

When to train it
The Latissimus Dorsi participates to throw movements and is advantageous to train for swimming, volleyball, climbing and in general athletes who use the upper limbs.

Pad placement
To stimulate the Latissimus Dorsi the electrodes have to be placed to recruit a good portion of the muscle fibers. The active lectrode is a large rectangular one, the inactive electrodes are two square ones.[ul]
[li]Inactive electrode: below the armpit; the upper side should almost touch the lateral side of the scapula.
[/li][li]Active Electrodes: they must be positioned, one above the other, at the level of the last dorsal vertebrae and the first lumbar vertebrae.
[/li][/ul]
To be continued by next muscle group: Adductors.

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ADDUCTORS
The adductor group is composed of 4 muscles contributing to the same functional movement: adductor brevis, adductor longus, adductor magnus and pectineus. Origin is on the pubis and ischium. The insertion is on the femur at different points. The main function is the adduction of the leg toward the other leg.

When to train it
The adductors are important in all flexion-extension movements of the thigh, and therefore are important for dance and gymnastic. Riding sports also use these muscles. They are also important aesthetically, since their tone determines the shape of the inside of the upper leg.

Pad placement
[ul]
[li]Active electrode: below the pubic origin of the adductors, at the center of the inner side.
[/li][li]Inactive electrode: at about one third of the length of the thigh, starting from the pubis origin.
[/li][/ul]

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I’d like to underline a very important and misunderstood feature of EMS, recruitment order. In a nutshell: muscle fibers are not recruited in reversed order and there is no apparent sequencing related to muscle fiber type; recruitment reversal reflects beliefs based on past findings that are being questioned and proven incorrect. The next quote is an example of how rooted this belief is.

Voluntary muscle activation activates muscle fibers in a very specific order, from smallest Slow-Twitch (ST) fibers, to largest Fast-Twitch (FT) fibers. Early research seemed to point out that this was reversed in EMS exercise: FT fibers were activated more easily than ST fibers. However, very recent research has demonstrates that EMS does not reverse the natural recruitment order, and it rather activates fibers based on position relative to the electrode pads.

Voluntary recruitment order, as quoted from Zatsiorsky’s & Kraemer’s - Science and Practice of Strength Training, Human Kinetics, Champaign, IL:

The orderly recruitment of MUs (Motor Units) is controlled by the size of motorneurons (Hennemann’s size principle): Small motorneurons are recruited first, and requirements for higher forces are met by the activation of the large motoneurones that innerfate fast MUs.

Early studies that experimented on single fibers in a lab setting, found that FT larger fibers were easier to excite: see Gorman and Mortimer, The effect of stimulus parameters on the recruitment characteristics of direct nerve stimulation; IEEE Trans. Biomed.Eng. 1983
However, those studies were performed on anesthetized animals, attaching electrodes directly to muscle fibers by cutting through the skin. Since this were the only available findings at the time, the literature on EMS started using this as a self fulfilling benchmark.

Clinical Electrophysiology, a sacred reference textbook on EMS says (Robinson, Snyder-Mackler; 1995, Williams and Wilkins):

For isolated motor nerve situation, the pattern of recruitment tends to be in order from largest-diameter to smallest-diameter fiber…
Stimulated contraction occurs by an activation of type FF (fast-twitch, fatigable) motor units first, followed by type FR (fast-twitch, fatigue-resistant) and ending with type S (slow-twitch, fatigue-resistant) units. This reversed order of motor unit recruitment in electrically induced contractions is not stable as that for voluntary contraction. For example, if the axons of fatigue-resistant units are located significantly closer to the stimulating electrodes than axons for type FF units, these units may be recruited before the fatigable type.

So you can start seeing above some exception to the, until then, complete belief in the reversed-recruitment-order principle. More recent research has actually confirmed that there isn’t actually an order, but rather an indiscriminate recruitment: the peer-reviewed article, Recruitment Patterns in Human Skeletal Muscle During Electrical Stimulation, Gregory and Bickel, Phys Ther, Apr.2005, says:
.

Previous studies as well as some commonly used textbooks,18,19 presume the reversal of recruitment pattern based on studies of lower mammals. However, factors that affect current flow, and therefore muscle activation in vivo (ie, skin impedance, subcutaneous fat, peripheral nerve orientation, and so on), result in a different physiological environment relative to the animal studies. Thus, although the neurophysiological principles commonly used to support a reversal of recruitment order are based on well designed studies, these principles do not strictly apply during typical EMS applications to humans.

Jubeau et al. verified this hypothesis in the peer-reviewed published research, Random Motor Unit Activation by Electrostimulation, Int J Sports Med Nov.2007, concluding:

The present findings confirm the suggestions made by Gregory and Bickel, that MU recruitment pattern during NMES is random and nonselective. Over-the-muscle electrostimulation would neither result in motor unit recruitment according to Henneman’s size principle nor would it result in a reversal in voluntary recruitment order. During electrostimulation, muscle fibres are activated without obvious sequencing related to fiber type.

Understanding recruitment correctly is very important. The consequence is enormous: recruitment percentage is dictated by the depth of the electric field (which increases with increasing current intensity). ST and FT fibers are normally mixed in a muscle bundle, i.e. equally distant from the pads. Therefore stimulation frequency becomes the most important factor in deciding what type of work we are going to do with EMS training.

The importance of this very recent finding, for those who train for force development, will be explained in a future more-in-depth posting on stimulation frequency.

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Recruitment order is not well known but I covered the advantages of this many years ago.
First in an article published in 1981 and widely disseminated by various manufacturers over subsequent years, then in CFTS and also in some detail in the 2002 forum review.
EMS benefits and Individual session treatments are detailed in articles in the T-Nation archives as well.