Read the whole article from top to end…
The article is by Globus.
Modern EMS systems recruit muscle differently because they rely on action potentials, and threshold potentials that differ for each type of tissue.
MEMBRANE POTENTIAL
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 opposite charges on the two sides of the membrane creates an electrical field across it 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
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 motorneurons 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 muscles through their respective 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 itself, which switches the membrane potential from negative to positive. This polarity inversion is called Action Potential.
Purpose of the Action Potential
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
At rest the membrane potential is -70 mV.
External perturbation, i.e. stimulus, changes the membrane potential to -55 mV.
Beyond the threshold value the ion exchange mechanism triggers polarity inversion, i.e. the action potential, which is transmitted along the nervous fiber.
The action potential excites the membrane of the next cell, propagating the action potential mechanism to the target fiber.
What Happens 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.
Direct muscle stimulation refers to a current that bypasses the CNS and stimulates the muscle fibers…directly nothing to do with probes or plates directly on the muscle. The action potential needed to do this is usually greater hence you need a greater current and frequency. The threshold needed to stimulate muscle indirectly through nerves is much lower so you need a lower current and frequency. This has nothing to do with in vivo. Yes the Globus programmable has the Kots protocol available but the modern EMS protocols on the Globus and Compex work differently. Modern EMS systems can achieve the same effects as the Kots protocol but they rely on using Lapiques Law to achieve this. Its like the ball and chain principle. The threshold for stimulating nerve cells is on 70mv whilst the threshold for direct muscle stimulation is 90mv. Yet if you stimulate the nerve cells, the current is propagated down the nerve cells to the muscle, hence you can recruit the muscle indirectly. Please read the article carefully…