Electrical stimulation

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Under electrical stimulation is generally understood as the stimulation of the human body by externally applied electric fields.

Medical electrical stimulation - electrotherapy

When nerves in the periphery of the body fail , especially on the arms and legs, muscle cells in the muscle supplied by the paralyzed nerve break down . In order to avoid this, the activation of the affected nerves is simulated during a therapy session with the help of attached electrodes with low current surges. This stimulates the threatened muscle, so it moves again and does not atrophy .

The muscles react differently to different types of modulation of the current. In general, exponential voltage curves give the best results.

Electrical stimulation is also used in human medicine for men with anejaculation and in veterinary medicine to obtain ejaculate from breeding animals.

hazards

The human body reacts very sensitively to electrical currents : Even relatively small voltages (<40  V ) can lead to injuries ( burns , functional impairment of peripheral nerves, etc. ) under unfavorable conditions (e.g. heavy perspiration and therefore good electrical conductivity ) ; The conduction of excitation between the heart muscle cells can also be disturbed, leading to potentially life-threatening cardiac arrhythmias .

Functional electrical stimulation

As Functional Electrical Stimulation (FES) is the electrical stimulation of a muscle directly or indirectly via the motor nerve to perform a muscle contraction referred to that can be performed in two ways.

Probably the most successful and well-known application of implanted FES is the pacemaker . Depending on the damage, the heart muscle is usually electrically excited in the right atrium or in the right ventricle (see heart ).

Other FES implants: respiratory pacemaker (phrenic nerve stimulator), intestinal pacemaker , bladder pacemaker

Nerve stimulation

In nerve stimulation, an electric field strength with a sufficiently strong gradient is applied to trigger action potentials in the nerve , which travel along the motor neurons to the end plates in the innervated muscle. There they trigger action potentials, which subsequently cause the muscle to contract.

Muscle stimulation - electromyostimulation (EMS)

Fitness training with EMS

Here the muscle cell is excited directly by electrical stimuli; these stimuli have to be significantly larger and longer than when stimulating nerves. In both cases, functional electrical stimulation can be carried out with surface electrodes over the skin (as a rule during training and rehabilitation) or with implanted electrodes . By changing the EMS stimulus frequency, different areas of the muscle fiber spectrum can be stressed to different degrees. The stimulation current impulses alternate with short pauses. During the impulse phases, the muscle is brought above its stimulus threshold and muscle contraction occurs. The intervals mimic natural muscle movement. As soon as the person moves, the brain sends impulses to the muscles. By using stimulation current, the impulses are not sent from the inside but from the outside to the muscles, so that they contract during the impulse phase and relax during the breaks. In combination with movements, the effect increases and the muscles can be built up faster. Endurance cannot be improved by electrical stimulation. The electrical impulses are only suitable for building muscle. This form of stimulation is also known as EMS training and has been examined for its suitability for use by top athletes as well as for rehabilitation at least since the 1970s. Since the stimulation does not take place via the physiological path (nervous system → muscle), but takes place in a direct way, electromyostimulation can only be used to a limited extent. It can be done at rest or only combined with simple movements, so that the ability to coordinate is not improved accordingly. Overall, the scientific data on effectiveness is very thin and shows no comparable effect to physical training.

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In EMS, the muscle contraction induced by current leads to structural adjustments in the muscles, which are the basis for a measurably increased muscular performance. A systematic review of the relevant literature shows positive muscular adaptations in the area of ​​fiber cross-section, fiber composition and the activity of oxidative enzymes. Furthermore, neural adaptations in the sense of an improvement in the neural activation of the muscles were shown. Due to the positive effect of EMS on structural and functional muscle parameters and overall on muscular conductivity, this method is used both in therapy and in sports. In electromyostimulation, a distinction must be made between local EMS and whole-body electromyostimulation. With local EMS, electrodes are used to activate individual muscles or muscle groups in isolation. With whole-body EMS, several large muscle groups are activated simultaneously using special cuffs and vests with built-in electrodes, whereby agonists and antagonists are activated synchronously in the sense of a contraction.

EMS can be passive or active, i.e. without or with additional voluntary muscle activation. In active EMS, the current-induced and voluntary activation of the muscles overlap, resulting in a higher contraction strength. The muscle can be activated isometrically or dynamically at will. Sometimes more complex training exercises are carried out, the muscular effect of which is increased by EMS. The functional EMS is a special form, in which coordinated muscle contractions are generated in the presence of muscle paralysis, which facilitate walking or cycling (see below).

The EMS protocols used are very diverse, with predominantly biphasic pulses with a pulse duration between 100 and 500 μs and a low-frequency pulse frequency of 10–100 Hertz being used (so-called TENS currents). Medium-frequency alternating currents (1000–4000 Hz), which i. d. Usually a low-frequency modulation frequency (often 50 Hz) are used.

EMS areas of application

Sports

EMS is used in the field of sport to increase muscular performance and to support the systematic training process. The scientific data situation is now very extensive. A comprehensive systematic review of the literature, which included 89 scientific studies with untrained and trained healthy test subjects, showed a significant and mostly pronounced effect of EMS on parameters of muscular performance (including maximum strength, speed strength). The studies showed z. B. in athletes after isometric EMS significant increases in terms of both isometric (mean + 32 ± 15.6%) and dynamic maximum strength (mean + 34.1 ± 21.7%). Similar effects also occur with untrained and dynamic EMS. The speed strength improved preferably through dynamic EMS training. The high effects on speed strength are attributed to the fact that the fast-twitch muscle fibers respond preferentially to EMS training, which are only recruited with voluntary training at maximum loads or movement speeds.

An analysis of the results of the study revealed an appropriate training frequency and duration, sufficient muscle contraction strength (≥50% of the maximum voluntary contraction strength), a pulse duration of 200 to 400 μs and a stimulation frequency of 50 to 100 Hz as guarantees of good effectiveness. Another literature analysis With the question of the optimal protocol, which included the strength of the sensitive discomfort and the frequency-dependent fatigue ("high frequency fatique") and thus reduced responsiveness of the muscles, the result was that a pulse duration of 400 to 600 μs and a frequency of 30 up to 50 Hz are ideal for muscle training.

The effect of medium-frequency currents on muscular performance parameters is less well studied. Only 4 of the 89 studies in the above Review by Filipovic et al. worked with medium-frequency currents (<1000 Hz). A recent meta-analysis showed that low-frequency and medium-frequency currents are similarly suitable for activating the muscles. This meta-analysis also showed that there are no differences between the methods in terms of sensitive discomfort. The old doctrine that medium-frequency currents are more sensory because of the reduction in skin resistance must therefore be revised. Contrary to earlier assumptions, there is also no difference between the two methods with regard to the resulting muscle damage and sore muscles (CK, DOMS). The effect of medium-frequency currents, however, depends on the current shape. The modulated 2500 Hz currents ("Russian"), which were preferred for a long time, proved to be inferior to the modulated 1000 Hz currents ("Aussie") and low-frequency TENS currents with regard to the activation of the muscles and the sensitive discomfort.

If one compares the effects achieved by EMS with those generated by conventional strength training, the few studies show a heterogeneous result with some effects in favor of EMS. partly in favor of strength training. or without distinction, Hainault and Duchateau therefore concluded that "the strength gains through EMS are comparable, but not greater, than through voluntary training"

But EMS seems to be a useful addition to training because of the peculiarity of stimulus setting and the specificity of the adaptations, which cannot be implemented in this form by conventional arbitrary training and to be able to make a contribution to the realization of the training principles of stimulus increase and stimulus variation. With a view to the study results of the above Analysis, Filipovic et al. Conclude that EMS is a promising approach to increasing muscular performance parameters.

The point of criticism of EMS is the lack of coordination training, as the (feedback) mechanisms of the central nervous control of the muscles are not used. In this context, however, it should be noted that studies have shown an electromyographically measurable improvement in the neuronal activation of the muscles after EMS training. which proves a central nervous adjustment. The EMS-induced improvement in muscle control is probably due to the fact that muscle activation occurs not only directly via peripheral nerve branches, but also indirectly via reflex activation of motor neurons. Furthermore, activation of motor brain areas by EMS was observed. However, since movement control in terms of sensorimotor feedback mechanisms is not adequately trained with EMS, EMS training should ideally be combined with conventional functional exercises or proprioceptive training. In principle, there is also the possibility of increasing the effect on the muscles when performing complex exercises by simultaneously applying EMS. In summary, it can be stated that EMS training is a specific and special form of muscle training with which one cannot train all dimensions of athletic performance. Accordingly, EMS can complement, but not replace, athletic training.

Heinz Kleinöder from the Institute for Training Science and Sports Informatics at the German Sport University in Cologne sees electromyostimulation as a "sensible training method (...) especially for people with little time and for athletes who want to control large muscle groups at the same time." EMS training, which originally came from therapeutic application, now plays an important role in professional and popular sports. In Germany, around 140,000 people now train with around 1,500 full-body EMS providers (as of December 2015). Many of the providers are organized as so-called micro studios.

therapy

On the question of the medical application of EMS, a current, comprehensive Cochrane Review addresses the effect of EMS in the case of muscle weakness in patients with advanced diseases (chronic lung, heart disease, cancer). Based on the analysis of 18 publications (933 patient data), the authors conclude that EMS, which improved strength, muscle mass and walking ability in the 6-minute walking test, is an effective measure against muscle weakness and as a treatment measure in the context of rehabilitation programs should be considered. In all 18 studies, low-frequency TENS currents were used (15 to 75 Hz, 200 to 700 μs).

In the orthopedic field, EMS has shown good results in chronic back pain related to back strength and pain in studies. The effect on osteoarthritis is unclear, although a new meta-analysis showed a pain-relieving effect on knee osteoarthritis.

In the neurological area, EMS v. a. use for peripheral nerve damage. The use of EMS for partial denervation of peripheral nerves has long been extremely controversial. However, recent studies clearly demonstrate the benefit of reducing the atrophy of the muscles and re-innervation, which is probably caused, among other things, by the release of neurotrophic factors. In central nervous neurological diseases, the use of classic EMS is less widespread and hardly researched. Functional electromyostimulation (FES) is used in the case of corresponding clinical pictures such as hemiplegia or multiple sclerosis, the aim of which is to reduce motor deficits by activating the muscles and thus improving grip or walking function through coordinated impulses. In the case of complete paraplegia, FES is used to coordinate muscle activity on a bicycle ergometer or on a leg press. The potential of FES in the context of rehabilitation is illustrated by a study in which FES training on the bicycle ergometer in paraplegic patients had a positive effect on neurological function, muscle mass and structure, functional abilities, spasticity and, ultimately, quality of life.

EMS has advantages especially in therapy: (1) First, the training is subjectively less strenuous than conventional strength training, according to which the inhibition threshold for carrying it out is lower in patients with exhaustion syndrome. (2) Second, muscle activation can be achieved with a simultaneous low stress on the joints, which is particularly important in the phase of partial stress. (3) Thirdly, the types of current used in EMS also have a positive effect on pain perception, whereby the pain-relieving effect is comparable with currents in the low-frequency range and currents in the kilohertz range.

Electrostimulation through cochlear implant

Another area of ​​application for electrical stimulation is in ENT . The cochlear implant is used here, which can enable hearing with severe hearing loss or even with deafness through direct electrical stimulation of the auditory nerve.

The electrical stimulation takes place at different points of the scala tympani , whereby different sections of the basilar membrane and the associated ganglion cells of the hearing organ are stimulated. This leads to a tonotopic stimulation and a simulation of the frequency-location transformation of the normal inner ear. Furthermore, the temporal structure of the acoustic information is transmitted via the stimulus rate at each electrode.

After a good adjustment of the speech processor and with enough practice, patients with cochlear implants can not only understand speech, but can also listen to music or make phone calls. Above all, children who were born with severe hearing loss need a lot of hearing training in order to learn to hear and thus to be able to have the opportunity to speak actively.

Electrostimulation of completely denerved muscles

The only effective way to train denervated muscles (permanent, complete peripheral paralysis) is to use electrical stimulation with pulses of 40–300 ms pulse width and intensities of up to 250 mA for direct muscle stimulation. This means that strength training can be carried out using tetanic contractions, which leads to structural and functionally measurable improvements.

See also

Individual evidence

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