The use of electric current on the human body largely has been restricted to use by physiotherapists to facilitate the healing of musculoskeletal injuries and control pain, but the regular appearance of advertisements in muscle magazines trying to sell these devices to increase muscle bulk or slimming the waist line without lifting a finger suggests that its appeal may be beconing more widespread. Are these claims valid? Can electrostimulation (ES) play some role in sports and fitness training?
Let us begin by commenting that ES may be fairly arbitrarily applied in two broad categories:
- Macrocurrent Stimulation (currents over about 1 milliamp)
- Microcurrent Stimulation (currents below about 1 milliamp)
The former usually refers to Faradic, Interferential, Galvanic and TENS (Transcutaneous Electrical Nerve Stimulation) devices, whereas the latter refers to specialized microcurrent devices for application either to the musculoskeletal system or as a non-invasive form of electroacupuncture via the acupuncture points of the body or the auricular points of the ears. The differences between these applications will be discussed later in this article.
The concept of electrostimulation for physical conditioning is not new, and for years has been used by physical therapists in clinical applications such as muscle rehabilitation, relief of muscular spasm, reduction of swelling and pain control. Its possible value in sports training is still considered controversial. In strength conditioning, the potential applications of electrostimulation fall into the following broad categories:
- Imposition of local physical stress to stimulate supercompensation
- Local restoration after exercise or injury
- General central nervous and endocrine restoration after exercise or injury
- Neuromuscular stimulation for pain control or movement patterning
Electrostimulation usually involves feeding the muscles low current electrical impulses via moistened electrode pads placed firmly on the skin. The effectiveness, comfort and depth of excitation depends on factors such as pulse shape, frequency, duration, intensity and modulation pattern. The resulting number of possible stimulation combinations immediately emphasizes how difficult it is to determine the optimum balance of variables and compare the results of different researchers.
The typical clinical machine supplies pulsating direct (galvanic) and/or alternating (faradic) current in the form of brief pulses. The frequency of faradic current is most commonly chosen in the range of about 50-100 Hz, while pulse duration (width) ranges from about 100 microseconds to several hundred milliseconds. This brevity of pulse duration is important for minimizing skin irritation and tissue damage. However, the duration at any particular intensity of faradic stimulation should not be too brief. Although they may be suitable for decreasing pain, pulses that are too brief will supply insufficient energy to cause full, tetanic muscle contraction.
Machines are designed to apply alternating currents directly at a preset or selected frequency (conventional faradism), or in the form of low frequency currents superimposed on a medium frequency (2000 to 5000 Hz) carrier wave. A variation of the latter method, using two pairs of electrodes each supplying medium frequency waves carrying low frequency waves differing slightly in frequency, forms the basis of what is called interferential stimulation. A major advantage of using a higher frequency carrier wave is that impedance between the electrodes and skin is lowered, enhancing comfort and effectiveness.
American interest in electrostimulation as a training adjunct was aroused in 1971, when Kots in Russia reported increases of more than 20% in muscle strength, speed and power produced by several weeks of electrotraining. Unable to produce comparable results, the Canadians invited him to lecture at Concordia University in 1977. Armed with the new information that Kots employed a sinusoidally modulated 2500 Hz current source applied in a sequence of 10 seconds of contraction followed by 50 seconds of relaxation, they again tried to duplicate Russian claims.
APPLICATIONS OF MACROCURRENT STIMULATION
A literature review reveals the following major uses of macrocurrent stimulation in the realm of therapy. A more detailed discussion or the citations are not quoted here, but appear in my review on this topic [Siff M C (1990) Applications of electrostimulation in physical conditioning: a review J of Appl Sports Science Res 4 (1) : 20-26 ], as well as in the textbook: Siff MC (2000) Supertraining, Ch 4.
- Increase in muscle strength
- Re-education of muscle action
- Facilitation of muscle contraction in dysfunctional or unused muscle
- Increase of muscular and general endurance
- Increase in speed of muscle contraction
- Increase in local blood supply
- Provision of massage
- Relief of pain
- Reduction of muscle spasm
- Promotion of relaxation and recuperation
- Increase in range of movement
- Reduction of swelling
- Reduction of musculoskeletal abnormalities
- Preferential recruitment of specific muscle groups
- Acute increase in strength
- Improvement in metabolic efficiency
THE EMERGENCE OF MICROCURRENT STIMULATION
Recent research and clinical experience have revealed that electric currents as much as 1000 times smaller than that of all the traditional physical therapy modalities can be far more successful than the latter in achieving many of the benefits outlined in the previous section.
Currents as low as 10 microamps (millionths of an amp) pulsating at between 0.1 to 400Hz are too weak to cause muscle contraction, block pain signals or cause local heating, yet their effectiveness and safety is often superior in many applications to that of faradism, interferentialism and conventional TENS (Matteson & Eberhardt, 1985).
The steps to satisfactorily modify the existing paradigm for ES may be sought in the research findings quoted earlier in the section: 'Reasons for conflicting research'. There, it was learned that cellular and subcellular processes not involving cell discharge, propagated electrical impulses, or muscle contraction, appear to be involved with cellular growth and repair.
Some studies have produced findings which offer partial answers to the questions posed by microstimulation. For instance, work by Becker and others suggests that small, steady or slowly varying currents can cause subthreshold modulation of the electric fields across nerve and glial cells, thereby directly regulating cell growth and communication (Becker, 1974; Becker & Marino, 1982). In this respect, some of Becker's applications included the acceleration of wound healing, partial regeneration of amphibian and rat limbs, and induction of narcosis with transcranial currents. Nordenström maintains that these electric currents can stimulate the flow of ions along the blood vessels and through the cell membranes which constitute the body's closed electric circuits postulated by his theory (Nordenström, 1983).
Pilla (1974) has paid particular attention to electrochemical information transfer across cell membranes. The model in this case hypothesizes that the molecular structure of the cell membrane reflects its current genetic activity. Here, the function of a cell at any instant is determined by feedback between DNA in the cell nucleus and a macromolecule inducer liberated from the membrane by means of a protein (enzyme) regulator derived from messenger RNA activity within the cell. The activity of these membrane-bound proteins is strongly modulated by changes in the concentration of divalent ions (such as calcium Ca++) absorbed on the membrane. ES may elicit these ionic changes and thereby modify cell function.
It has been shown that ES at 5Hz stimulates synthesis of DNA in chick cartilage cells and rat bone by as much as 27%, but not in chick skin fibroblasts or rat spleen lymphocytes (Rodan et al, 1978). Not only does the effect of ES appear to be tissue-specific, but the increase in DNA synthesis occurs 4-6 hours after 15 minutes of ES. The process of membrane depolarisation carried by sodium ions seems to be followed by an increase in intracellular Ca++ concentration, thereby triggering DNA synthesis in cells susceptible to the particular stimulus. Further work by Pilla (1981) has confirmed the existence of cellular 'windows' which open most effectively to certain frequencies, pulse widths and pulse amplitudes. To attune the ES signal to these parameters, monitoring of tissue impedances is preferable, a system employed by so-called 'Intelligent TENS' devices.
In addition, Cheng et al (1982) have shown that stimulation with currents from 50-1000 microamps can increase tissue ATP concentrations in rats by 300-500%, and enhances amino acid transport through the cell membrane and consequent protein synthesis by as much as 40%. Interestingly, the same study reported that increasing the current above only one milliamp was sufficient to depress tissue ATP and protein synthesis - and traditional ES most commonly applies currents exceeding 20 milliamps, at which stage this depression being nearly 50%.
AN INTEGRATED THEORY OF ELECTROSTIMULATION
Therefore, it appears as if macrocurrent stimulation (MACS - currents exceeding one milliamp) acts as a physiological stressor, which in the short term causes the typical alarm response described by Selye (1975). This is supported by the work of Eriksson et al (1981), who found that the acute effects of traditional ES are similar to those found for intense voluntary exercise. Furthermore, Gambke et al (1985) have found in animal studies that long-term MACS causes some muscle fibres to degenerate and be replaced by newly formed fibres from satellite cell proliferation. This fibre necrosis occurs a few days after application of ES and seems to affect mainly the FT fibres. The fact that the various muscle fibres do not transform at the same time may be due to different thresholds of each fibre to the stimulus that elicits the transformation. Possibly, the earlier changes might induce subsequent ones.
Thus, if Selye's General Adaptation Syndrome model is applied to MACS-type stimulation, the body would have to draw on its superficial adaptation energy stores and adapt to the ES-imposed stress by increasing strength or endurance, or by initiating transformation of muscle fibre types. If the ES is too intense, too prolonged or inappropriately used to augment a weight-training program, adaptation might not occur or it might increase the proportion of slow twitch fibres and thereby reduce strength. This could explain some of the negative research findings discussed earlier.
Furthermore, excessively demanding MACS conceivably might cause the body to draw on its deep adaptation energy and lead to permanent tissue damage. Consequently, any athlete who may derive definite performance benefits from MACS should not assume that increased dosage will lead to further improvement. The contrary may well prove to be true.
Microcurrent stimulation (MICS - currents below one milliamp), on the other hand, would not act as a stressor. Instead, the evidence implies that it elicits biochemical changes associated with enhanced adaptation, growth and repair. Since MICS appears to operate more on the basis of resonant attunement of the stimulus to cellular and subcellular processes, the specific therapeutic effects are determined by how efficiently the stimulation parameters match the electrical characteristic of the different cells, in particular, their impedance at different frequencies. MICS may be applied in several ways to facilitate restoration:
- locally over specific soft tissues
- transcranially via electrodes on the earlobes or on sites on the surface of the skull
- at acupuncture points on the body, hands or ears.
It is generally entirely safe to apply MICS anywhere on the body, because the current and energy transmitted is too low to produce any thermal or electrolytic effects on vital tissues. Under no circumstances should MACS be applied across the brain, as it can cause serious harm. It is generally not advisable to apply any form of ES to epileptics, pregnant women, cardiac patients or persons with heart pacemakers.
THE VALIDITY OF MICROCURRENT APPLICATION
There has been considerable debate about the value of microcurrent (small electrical currents of less than 1 ampere) in physical therapy, with its supporters claiming consistently good results and its detractors claiming that any benefits are probably due to a placebo effect. Some therapists have stated that there is scant evidence of any research and practical evidence of the value of microcurrent, so, for their interest and that of others conducting research into microcurrent therapy, I have compiled a lengthy, but incomplete, list of English language references that relate to the theoretical foundations and clinical applications of microcurrent (available on request).
My own interest in this field was piqued while I was gathering research information for my M.Sc into the mechanisms underlying the electroencephalogram (EEG) in brain research. While browsing in the old science library located in the physics building at the University of the Witwatersrand, South Africa during 1971, I encountered a few fascinating texts: one edited by Barnothy (1969) and another by Presman (1970), as well as several articles by Robert Becker, with whom I later had periodic contact over the years. It was these few texts which led to my prolonged interest in this field.
THE USE OF ELECTROSTIMULATION IN TRAINING
The summary of successful applications of ES in numerous situations which are relevant to all athletes makes it unfortunate that its value has been assessed largely in terms of its direct and often contradictory effects on isometric or isokinetic strength. Enhanced recuperation, improved endurance, diminished residual muscle tension, pain relief, efficient massage, modification of muscle fibre type, increase in mobility, increased speed of muscle contraction and reduction of certain musculoskeletal abnormalities together supply an impressive variety of possible aids to any training programme. Coupled with this is the observation that some ES procedures integrated into carefully periodised training schedules may significantly increase strength, muscular endurance and power.
THE INTEGRATED USE OF ELECTROSTIMULATION
Electrostimulation can provide a valuable additional means of restoration and is generally of greater importance than as a means of stressing the muscles. This type of restoration (Siff & Yessis, 1992) may be applied locally to specific muscle groups, other soft tissues or joints, or generally across the central nervous system (transcranially, on specific acupuncture points or between the brain and the lumbar spine), using very low current devices at low frequencies (characteristically between 0.5-8 Hz).
Several researchers (Purvin, Deniskin, Khodykin) studied the integration of ES into other regimes of training. They found that the use of ES first, followed by plyometrics produces a greater training effect than the reverse order of these means. However, a still larger effect was obtained by using ES and plyometrics concurrently with heavy resistance exercise, with the ES and plyometric combination having the smallest training effect during periods of complete or partial rest.
In applying the ES, the placement or configuration of electrodes is also very important, since one can use essentially two methods: adjacent or distant attachment. Adjacent or close attachment of the two electrodes tends to localise the muscle contraction and keep it fairly superficial, whereas the distant attachment method (where one electrode is attached to a remote or fairly neutral location from the muscle being stimulated) tends to produce a more extensive, deeper form of muscle contraction. To ensure good and comfortable conduction between electrode and athlete, it is vital to lubricate the area of attachment with a commercial electrode gel or weak saline solution. Any signs of superficial skin irritation or prickliness invariably are the result of the gel drying out. The electrodes may also be used directly over important nerves, but the intensity of the ensuing contraction can be harmful and this method should be restricted to use by experienced physical therapists.
The unified concept of the various ES modalities presented here should enable the scientist or therapist to approach the issue of electrostimulation more systematically. Thus, if additional stress is needed on particular muscle groups to elicit more pronounced supercompensation, the MACS modality should be employed by using faradic or interferential-type devices applied with gradual overload of both training and ES intensity.
SPORTS FUNCTIONAL ELECTROSTIMULATION
Little or no mention is made in the West of the application of FES (Functional Electrostimulation) in sports training. In the West, this term or its equivalent FENS (Functional Electroneural Stimulation) invariably applies to the use of electrostimulation to contract the muscles of spinally disabled patients who cannot voluntarily activate their muscles and offer some degree of externally controlled movement. In Russia and other Eastern European countries the terms can also apply to the application of electrostimulation to able-bodied athletes during natural sporting movements to intensify muscle tension at the most appropriate phases of these movements. The innovative Professor Igor Ratov of the State Central Institute of Sports Science in Moscow, has done considerable research in this field with able-bodied and disabled subjects and stresses that this type of functional stimulation is far more consistently successful than the passive methods attributed to Kots by his Western supporters.
Work that I witnessed in his laboratory involved the use of concurrent EMG recordings to phase the FES correctly into specific sporting movements, most specifically to avoid producing spurious muscle tension or uncoordinated movement. Eventually, athletes learn to contract their muscles synchronously with the externally applied electrical field and thereby produce greater strength, power and speed. This method is sometimes called active electrostimulation, since the ES is applied to active muscles rather than to relaxed muscles (passive electrostimulation), which is the method most commonly used in physical therapy.
The use of highly specific methods like sports FES should not lead us to exclude the possible importance of general methods of ES which intentionally avoid offering any form of functional training. In this respect, the ES training applied to the author by Serge Reding used a special stimulator that was designed to offer external stimulation which in no way simulated the most frequently occurring movements of Olympic lifting. In other words, ES may also be used as a form of GPP (General Physical Preparation). The Reding machine applied brief intense pulses alternately in a flip-flop fashion to opposite sides of the body, though not to paired agonists and antagonists. The intensity of the ES was carefully periodised into the entire training programme alongside other key methods of strength training and training sessions were always terminated with brief, deep ES muscle massage and restorative microstimulation across the brain and along the length of the spinal cord. Reding stressed the importance of different waveforms and regimes of FES for different categories of sport, adding that the method shared by Kots with Canadian coaches was only one of many possibilities.
OVERTRAINING AND RESTORATION
The possibility of overtraining, however, must be considered, especially if ES is being added to an already strenuous training program. It is generally not advisable to apply more than 5-10 minutes of intense ES per major muscle group, due to the associated tissue necrosis and prolonged soreness that may follow in the days after treatment. The use of biofeedback TENS devices which monitor cellular electrical characteristics and adjust the stimulating parameters automatically, limits the possibility of overstimulation or cell damage.
In general, MICS may be used far more routinely than MACS, since it cannot produce overtraining or injury and since it can accelerate recovery after training. Therefore, it can enable one to train more intensively and recuperate more rapidly between workouts and even between sets, if necessary. For the serious athlete who intends to periodically supplement strenuous weight training with MACS, regular use of MICS as well could prove invaluable in improving performance and minimising the chance of overtraining. It should be remembered, however, that routine or frequent use of accelerated methods of restoration can impair the natural ability of the body to recuperate and adapt; it is sometimes important to allow the body to undergo partial or unaccelerated restoration to facilitate the supercompensatory response (Siff & Yessis, 1992).
The untutored reader is not encouraged to use ES, since it requires considerable theoretical and practical training for its safe and effective application. Those who experiment casually with such devices in training generally note sporadic or short-term progress and discontinue their use after just a few months. Unless applied by experts in their use, these machines are usually a waste of money or disappointing in not living up to their advertised claims.
In several countries (such as the USA), ES devices generally may not be sold to the public or used commercially or therapeutically on any clients by anyone who is not trained in medicine or physiotherapy.
- There are several hundred references on this topic. Anyone interested in obtaining a copy of this list is welcome to contact the author at: firstname.lastname@example.org
- For those who have access to the textbook, Siff MC Supertraining 2000, Chapter 4 contains much more detail on this topic, as well as listing of many of the relevant references.