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The references and pictures can be found in the book.
My book provides a detailed discussion on NMES, covering: stimulation of innervated muscles with low-frequency (LF) impulse current (TENS-like) and medium-frequency (MF) current, stimulation to improve kinesthesia, stimulation for incontinence, and stimulation of denervated muscles. Here's a sample:
Muscle Stimulation with Medium-Frequency Alternating Currents
In addition to low-frequency, TENS-like impulse currents, medium-frequency alternating currents, also called kilohertz currents, are used to stimulate innervated muscles. The use of this current type became very popular after reports in the 1970s of the alleged great successes of so-called Russian Stimulation. This method was said to be not only particularly effective but also more comfortable than LF stimulation (Andrianova et al., 1974).
The impulses of an MF current are very short (125 µs at 4000 Hz, 200 µs at 2500 Hz), so only an intact nerve-muscle complex can respond to them. Stimulation occurs at the nerve (indirectly
), which transmits the action potentials to the muscle. In cases of peripheral nerve lesions, these currents are ineffective, and longer triangular impulses are needed, where stimulation occurs at the muscle itself (directly
). Claims that MF currents act directly
on the muscle are not supported by evidence.
BMAC and Russian Stimulation
Various terms are used to describe these kilohertz currents. The best-known are the tetrapolar exogenous interference according to Nemec and the bipolar endogenous interference, also called premodulated interference. The classic tetrapolar version should no longer be used for strengthening, as it is completely impossible to achieve targeted stimulation with it. The reasons for this are explained in the book's chapter on interference currents.
Premodulated IF is not effective for strength development because part of the impulses in the sinusoidal burst remain subthreshold and ineffective (Variant D in the figure). In contrast, Russian Stimulation (RS) divides a continuous sinusoidal 2500 Hz alternating current into 10 ms bursts, and the frequency of these bursts can be adjusted on the device. All pulses in the burst have the same intensity (= amplitude), making this method significantly more effective than the two mentioned above (C in the figure). This is a frequency-modulated medium-frequency alternating current, commonly called Burst Mode Alternating Current (BMAC) (Ward et al., 2004, Ward 2009, Ward et al., 2009).
Russian Stimulation or BMAC = bottom left (C). Bottom right (D) = premodulated MF current. From Ward 2009, with kind permission.
History of Russian Stimulation
Russian Stimulation became popular in the 1970s due to the allegedly excellent results of Dr. Yakov Koz (also spelled Kotz
or Kots
), then a professor of physical culture at the State Academy of Moscow. Dr. Koz administered electrical stimulations to his athletes and cosmonauts as a supplement to regular training and claimed that his method could achieve strength increases of around 40% in three weeks. These claims could not be confirmed during an exchange program in Canada in 1977 (Ward and Shkuratova, 2002). It was even claimed that Canadian elite weightlifters selected for the trials categorically refused to undergo this torture.
Koz's reasoning for combining active training with EMS was as follows. At the time, training focused primarily on volume and strength, targeting primarily slow-twitch motor units, which fatigue slowly and are innervated by Aα2 neurons. It was already known that electrical stimulation primarily stimulates fast-twitch motor units, which are responsible for rapid, precise movements and are innervated by Aα1 motor neurons. Combining the two methods thus activated both motor unit types.
Originally, Koz used a low-frequency 50 Hz rectangular impulse current with a phase duration of 1 ms (neofaradic). Through experimentation, he found that a 10-50-10
mode was optimal for training: 10 seconds maximum tension, 50 seconds rest, repeated 10 times, once a day (Andrianova et al., 1974). Initially, Koz did not use medium-frequency currents; these were introduced later and had slightly different effects on fatigue.
Medium-Frequency Currents and Training Efficacy
From a physiological perspective, the current and training form Koz developed make sense: at a stimulation frequency of 50 Hz, fatigue results from depletion of neurotransmitter reserves and conduction problems in the T-tubule system, rather than from fatigue effects that would lead to improved training condition. Avoiding fatigue is sensible, hence the 50-second rest period.
Later, other researchers replaced Koz's current form with a medium-frequency impulse current (Andrianova et al., 1974). This MF current, divided into 50 Hz bursts with a base frequency of 2500 Hz, causes relatively rapid fatigue through these same mechanisms and is therefore less effective than Koz's original form. However, higher frequencies are undoubtedly much more comfortable for training.
Stimulation can occur either directly on the muscle (via the motor stimulation zones), with Andrianova finding that frequencies around 2500 Hz were optimal, or indirectly
on the nerve at frequencies around 1000 Hz. This distinction is purely academic, as the very short impulses always stimulate the nerve. Koz's claim that the training was painless due to the frequencies used must be qualified: his users, elite athletes in the former USSR, were accustomed to enduring significant discomfort to remain competitive. This should be seen in the context of the spirit of the times.
BMAC and Aussie Stimulation
For many years, Australian researchers around Alex Ward have been working on RS and have tried to optimize the stimulation for compatibility and effectiveness. They found that a 1000 Hz alternating current applied in 2 ms to 4 ms bursts was optimal (Ward, 2009). This current quickly became known as Aussie Stimulation, in reference to RS. To avoid confusion, the term Burst Mode Alternating Current (BMAC) was later introduced, as it precisely describes the method and allows researchers to use their preferred parameters, provided these are correctly reported.
New Variants and Effectiveness
A new current form has recently joined the field: Burst Modulated Biphasic Pulsed Current (BMBPC). In BMAC, bursts consist of sinusoidal single pulses, as in RS, whereas BMBPC forms bursts from a rectangular pulse current.
Both 1000 Hz BMAC and 1000 Hz BMBPC appear equally effective for strength development and are significantly more effective than 2500 Hz BMAC (Russian Stimulation) (Adams et al., 2018).
Whether BMAC is more effective than NF stimulation for strength development is debated, though NF stimulation seems to have the edge. Studies show mixed results: some favor NF stimulation, others BMAC. Factors such as phase duration and user comfort play critical roles.