Theoretical Foundations of Muscle Stimulation, Not Just for Athletes

Muscle stimulation (also called electrical muscle stimulation, EMS – the English abbreviation for Electrical Muscle Stimulation) is a technology in which electrical impulses are applied to muscles to make them contract. Although there are serious physiological principles behind muscle excitation, the core idea is relatively simple to grasp. The aim is to have the muscle work not only when the central nervous system (brain, spinal cord) sends the instruction, but also to be able to induce it to operate artificially.

This method is not new. It was already used in Russian elite sports in the 1960s, and later it played an increasing role in rehabilitation, improving athletic performance, and more recently in personal home use.

But what actually happens in the muscles during stimulation? What physiological responses do different frequencies elicit? And why is it important that you understand exactly how it works?

What does it mean that a muscle contracts?

Before diving into the details of electrical stimulation, it is worth clarifying how muscles work.

The human body's muscles are made up of tiny "threads," called muscle fibers. These are controlled by the nervous system: when the brain decides we want to move a body part, it sends an electrical signal to the relevant muscle, which responds by contracting. This contraction creates movement.

In muscle stimulation, the device "imitates" this same process. The electrical impulses sent through the electrodes make no distinction to the muscle: it reacts as if the command came from the brain. This process is completely safe and, when used correctly, can be extremely effective for various purposes.

Muscle fiber types and how they work

There are different types of muscle fibers in our body.

Slow-twitch fibers (type I) – These fibers are responsible for muscular endurance. They can work for long periods at low intensity, for example during walking or maintaining posture. They use a lot of oxygen and fatigue relatively slowly.

Fast-twitch fibers (type II) – These fibers are activated in the muscle group when quick, explosive power is required, for example during sprinting or lifting a heavy object. They produce great force for a short time but tire quickly.

One major advantage of EMS (and a key difference from traditional training) is that stimulation can be targeted to activate certain muscle fiber types depending on the frequency used. By choosing the frequency, the desired effect can be precisely "planned".

The role of frequency in muscle stimulation

One of the most important characteristics of the electrical impulses used in stimulation is the frequency, measured in hertz (Hz). Frequency determines how many stimuli reach the muscle in one second.

This is crucial because different frequency ranges have different physiological effects.

1–10 Hz: Regeneration and increased circulation

Low-frequency stimulation primarily targets muscle recovery rather than strength increase. In this range, muscles contract gently and rhythmically, producing a sensation similar to a massage. This stimulates blood circulation, helps remove metabolic waste and speeds up healing.

This frequency range is often used for post-workout recovery or to treat chronically tired or overused muscles.

It also has a key role in musculoskeletal rehabilitation, especially in cases of paralysis or immobilization, when maintaining muscle activity is important.

10–20 Hz: Activation of postural muscles

In this range, contractions are somewhat more intense but still relatively slow and controlled. This stimulates postural muscles (e.g., deep back muscles, abdominal muscles), which can be especially important for spinal issues, poor posture or sedentary work.

This frequency is particularly suitable for use under physiotherapist supervision (combining exercises with stimulation), as it helps regain proper posture without excessively loading the joints.

20–50 Hz: General muscle strengthening

This is the frequency range most commonly used by muscle stimulation devices. Medium frequency yields stronger and more visible muscle contractions that force the muscle to do real "work." In this range mainly slow fibers contract, but fast fibers also partially engage.

The aim of this stimulation is muscle strengthening. It is excellent for increasing muscle tone, shaping, or for cases when someone wants to "wake up" their muscles again after a sedentary lifestyle or regain strength after a prolonged illness.

50–100 Hz: Maximal force production

High frequency produces very intense muscle contractions. This already acts like a "workout" for the muscle and can even increase maximal muscle strength.

For athletes, it can be an excellent supplement to weight training. It can be useful for developing important but hard-to-train muscle groups. It is also common that after an injury the muscles in the affected area lag behind the uninjured side — stimulation can speed up catching up.

High-frequency stimulation must not be overused! This type of stimulation is extremely demanding for the muscles. Its use is recommended only on well-trained, healthy muscles, for short periods, and adequate rest must be provided to the muscle after treatment.

The Henneman principle

Neuromuscular regulation of muscle activation follows the so-called Henneman principle (or Henneman's size principle), which states that the nervous system recruits muscle fibers according to their size: first the smaller, slow-twitch fibers (type I), and when more force is needed, the larger, fast-twitch fibers (type II) are also activated.

This is a finely regulated, energy-efficient system that, during natural movement, always mobilizes the smallest amount of muscle necessary.

In contrast, during muscle stimulation — since the electrical stimulus acts directly on the muscle and not through the nervous system — the recruitment order can be controlled!

With high frequencies you can even selectively activate fast fibers!

This is particularly useful in training because it helps work muscle fibers that would otherwise be less activated during natural movement, but it also means increased fatigue, so careful application is required.

What does a well-structured EMS session look like?

An effective muscle stimulation program should consist of several phases.

The first is the warm-up – here stimulation is applied at low frequency and mild intensity to increase blood flow and prepare the muscle for load. Then comes the actual work phase, where frequency and pulse duration are set according to the chosen goal (e.g., strength increase or tone enhancement).

Finally the cool-down, again at lower frequency to promote recovery.

A single treatment cycle typically lasts 15–30 minutes. It is important to always tailor the treatment to the body's condition: as a beginner, 2–3 sessions per week are sufficient; later this can be increased even to daily frequency.

Electrode placement – the key to success

One key to the effectiveness of EMS devices is precise electrode placement. Place one electrode over the belly of the muscle where it protrudes most. Place the other near the muscle origin, aligned with the direction of the muscle fibers.

This way you can ensure the electrical impulse travels as effectively as possible along the muscle, producing a natural contraction.

It is important that the electrodes do not cross each other and are not placed over joints, as this can reduce effectiveness and even cause discomfort.

Physiological response – what happens in the muscle?

When the electrical impulse reaches the muscle, ion exchange is triggered in the cell membrane, which initiates contraction. At this point the actin and myosin proteins in the muscle slide over each other, producing a mechanical contraction.

ATP is the molecule responsible for energy use. This substance can be produced in the presence of oxygen (aerobically) or without oxygen (anaerobically).

Different types of muscle fibers use energy differently, which also influences the frequencies at which they operate optimally.

Who is EMS recommended for?

Muscle stimulation has wide applications. It can be excellent for:

• Those leading a sedentary lifestyle
• Office workers with postural problems
• Athletes seeking performance enhancement
• Rehabilitation (e.g., after surgeries or injuries)
• Elderly people for maintaining muscle strength
• Postpartum recovery

However, it is important to note that EMS is not a miracle cure: it does not replace lifestyle, nutrition or exercise, but it can effectively complement them. It is especially useful for those for whom natural movement is limited or inhibited for some reason.

Muscle stimulation is a modern, well-controllable method to develop, maintain or restore muscle functions. Frequency selection is key — depending on which muscle fibers we want to activate and what physiological effect we aim to achieve. With proper use, EMS can support musculoskeletal health, improve quality of life and increase physical performance.