2. How Does EMS Work

3. Origins of EMS

4. NASA & Athletic Use

5. Clinical Studies

6. Sources

Neuromuscular Electrical Stimulation (NMES) – also known as electrical muscle stimulation (EMS) – is a technique that uses electrical impulses delivered through electrodes on the skin to cause muscles to contract. 

In essence, NMES mimics the body’s own nerve signals: an external stimulator sends currents through motor nerves, triggering muscle fibers to contract just as they would during normal movements.

This technology has been used for decades in physical therapy and sports training to strengthen muscles, improve endurance, and even maintain muscle function when voluntary movement is impaired.

Under normal conditions, your brain sends an electrical signal through nerves to muscle fibers, causing them to contract. 

NMES replaces that brain signal with an external one. Sticky electrode pads are placed on the skin over the target muscles, and a controlled electrical pulse is sent from an NMES device into the underlying motor nerves.

 This induces the muscle to contract involuntarily, as if the signal came from the central nervous system.

 By adjusting the stimulation parameters – such as pulse frequency, intensity (current amplitude), and pulse duration – clinicians or trainers can control the strength and quality of the muscle contraction. 

Research shows that increasing the frequency or pulse width of the current recruits more muscle fibers and produces stronger force output.

For example, frequencies around 30–50 Hz with longer pulse widths (~400 µs) tend to produce smooth, tetanic contractions optimal for muscle training without excessive fatigue.

One notable difference between electrically induced muscle contractions and natural voluntary contractions is the order of muscle-fiber recruitment. In normal use, the nervous system activates small, fatigue-resistant slow-twitch (Type I) fibers first, adding larger fast-twitch (Type II) fibers only as needed.

In NMES, the electrical current often stimulates larger nerve fibers first, so the fast-twitch muscle fibers fire earlier. This means NMES contractions can be quite strong (fast-twitch fibers produce high force) but also fatigue more quickly. 

The use of electrical muscle stimulation (EMS) for athletic performance began behind the Iron Curtain. Soviet sport scientists were pioneers in exploring EMS as a training aid for athletes as early as the 1950s.

The movement’s figurehead was Dr. Yakov Kots, a physiologist at the Central Institute of Physical Culture in Moscow. In the 1960s and 70s, Kots applied EMS to train elite Soviet athletes and reported remarkable results.

His most famous early finding – presented to Western experts at a 1977 symposium in Montreal – was that electrically evoked muscle contractions could generate greater tension than even a athlete’s maximal voluntary contraction.

In practical terms, Kots claimed EMS could boost an athlete’s strength by up to 30–40% in a short training period.

This specific EMS method (10 seconds contraction, 50 seconds rest, repeated for 10 minutes at a medium-frequency 2.5 kHz current) became known as the “Russian stimulation” protocol.

Kots even suggested that EMS might be more effective than conventional exercise alone for building strength.

Once the initial Soviet results became known, EMS gradually entered the Western sports training and sports medicine landscape. A key moment was the exposure of Kots’s work to Western experts around the 1976 Montreal Olympics and the 1977 USSR-Canada exchange symposium, which piqued global interest.

In summary, EMS technology has transitioned from a secretive Soviet-era experiment to a mainstream sports training and rehab modality. The early pioneering work of Dr. Yakov Kots in the 1960s–70s demonstrated the astonishing potential of electrostimulation to enhance muscle performance.

Subsequent research in the 1980s and 90s confirmed that potential – showing real strength and muscle gains from EMS, and integrating it into Western sports science.

In space, astronauts experience rapid muscle loss due to microgravity — especially in the lower limbs and postural muscles. Without Earth's gravity to provide resistance, even basic muscle functions like standing or walking are absent. As a result, astronauts can lose up to 20% of muscle mass and strength in a few weeks, especially in the quads, calves, and back.

To combat this, NASA and international space agencies (like ESA and Roscosmos) explored neuromuscular electrical stimulation (NMES) as a tool to maintain muscle tone and function without gravity. The concept: simulate exercise by electrically inducing contractions while the astronaut remains stationary or in bed rest.

NASA’s research validated that strong, externally induced muscle contractions can preserve muscle quality even without voluntary movement. This insight heavily influenced:

Injury recovery protocols (e.g., post-ACL or post-op NMES to reduce atrophy)

Periodized athletic training using EMS in deload or off-cycle phases (to maintain muscle without loading joints)

Performance Devices for Athletes

EMS tech originally designed for space medicine has been adapted for sports, such as:

Ape Born Fitness: Portable EMS units now used widely by athletes for strength training, warmup, and recovery. Their design was influenced by EMS parameter studies done in space analogs.

Whole-Body EMS and High-Tech Training

The concept of non-weight-bearing stimulation inspired whole-body EMS suits — labelled as “20-minute total workouts” that mimic resistance training. These suit systems borrow heavily from multi-electrode NMES setups tested in microgravity trials.

Dr. Toshio Moritani, Ph.D., reported significant improvements in abdominal strength, endurance, and posture, as well as reduced waist circumference, after a study involving NMES (Neuromuscular Electrical Stimulation). 

Specifically, the study participants experienced a 4.48 cm decrease in waist circumference, a 59% increase in abdominal strength, a 42% increase in plank duration, and a 121% increase in abdominal endurance. 

Furthermore, 74% reported improved posture, and 100% of the NMES group felt their midsections were more toned and firm.

Enhances Muscle Strength and Size: 

When used as a training tool, NMES can increase muscle strength and promote hypertrophy (muscle growth). 

Repeated muscle contractions from NMES training stimulate muscle fibers similar to resistance exercise.

Notably, scientific studies have found that adding NMES to regular strength workouts amplifies the gains – a recent meta-analysis showed that combining NMES with weight training led to significantly greater improvements in muscle strength and muscle mass compared to training without NMES.

Furthermore, NMES alone can be quite effective: a 2022 review concluded that NMES-only training produces strength gains virtually identical to traditional voluntary strength training, as long as the overall training intensity/volume is comparable

In other words, properly applied NMES can yield strength increases on par with conventional exercise, which has exciting implications for athletes looking to maximize strength or for individuals who cannot perform heavy workouts.

One of the earliest and most widespread uses of NMES is in rehabilitation – keeping muscles active when a person cannot move normally. 

Electrical stimulation helps maintain muscle mass and strength during periods of immobilization (for instance, after orthopedic surgery or while a limb is in a cast) and is used to prevent atrophy in bedridden or ICU.

NASA-sponsored research is even exploring NMES to counteract muscle atrophy in astronauts: in microgravity, muscles tend to weaken due to disuse, so astronauts on the International Space Station have tested wearable electrical stimulators to supplement their workouts and preserve muscle function in zero-gravity.

In clinical settings, NMES is effectively an “exercise alternative” for those who cannot perform voluntary exercise – for example, a Cochrane review found NMES can improve muscle strength in adults with advanced illness, essentially providing some benefits of exercise despite the patient’s limited mobility

In cases of paralysis or severe nerve injury, functional electrical stimulation systems allow patients to perform basic movements and exercise. 

For instance, FES cycling ergometers electrically activate the leg muscles of spinal cord injury patients, enabling them to pedal a stationary bike at a steady rate (around 50 RPM under resistance) and get a cardiovascular workout that reverses muscle atrophy and improves circulation

Such rehabilitative NMES not only preserves muscle bulk and strength but can also reduce secondary complications of paralysis, like poor blood flow and muscle spasmsspinoff.nasa.gov.

Improves Muscle Recovery and Circulation: Using EMS can increase local blood flow in muscles and has been shown to aid in muscle recovery after intense exercise or injury. 

The rhythmic contracting and relaxing of muscle fibers under electrical stimulation act like a pump for blood circulation.

Studies have noted that NMES boosts blood flow to stimulated muscles, which can speed up healing of injured tissues and help relieve muscle spasms or stiffness

Athletes sometimes use light NMES sessions on fatigued muscles (for example, after a hard training session) to enhance recovery – the increased circulation helps clear metabolic waste products and deliver nutrients to the muscle.

Emerging research also suggests NMES can improve aspects of metabolic health; for instance, by increasing muscle activity it may improve glucose uptake by muscles and has even been proposed to reduce the risk of blood clots in the legs by improving venous return in people who are very inactive

In practical terms, this means EMS might not only strengthen muscles but also keep them healthier and more resilient by improving their physiological environment (blood supply and metabolism). 

Some therapeutic devices (like the NMES unit NASA helped develop called the VST-100) are designed specifically to increase circulation and speed up recovery in injured or overused areas – one example is using NMES on a wrist with carpal tunnel syndrome to open up blood vessels and nerve pathways, thereby promoting healing and allowing a quicker return to work

Increases Muscle Endurance and Tone: NMES can also be utilized to improve muscular endurance and “tone” (the firmness or baseline strength of a muscle).

Because NMES can engage muscle fibers repeatedly over time, training programs using NMES have shown gains in muscular endurance – the muscle’s ability to sustain contractions longer.

In a notable 8-week study on abdominal muscles, participants who used an NMES device on their abs for 20–40 minutes a day, 5 days a week, achieved a 100% increase in abdominal muscle endurance and significant strength gains (~58% increase in isometric strength), without doing any additional exercise

The stimulation also had cosmetic benefits: the treatment group reduced their waist circumference by an average of 3.5 cm, and all participants reported that their midsections felt firmer and more toned after NMES

This evidence supports the idea that consistent EMS training can indeed firm up muscles and improve their functional endurance.

However, it’s worth noting that not all consumer-grade “ab stimulator” belts or EMS gadgets are equally effective.

Research has found that some off-the-shelf devices failed to produce any significant improvements in strength or appearance, largely because the electrical output was too low or uncomfortable to induce strong contractions

In practice, achieving real muscle toning or performance benefits with EMS requires using a high-quality stimulator at sufficient intensity to challenge the muscle (often contractions need to reach >50% of one’s maximal voluntary contraction to yield gains). 

When those conditions are met, EMS can indeed supplement traditional exercise by adding extra muscle contractions, thereby improving endurance and muscle firmness over time.

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Recruitment patterns in human skeletal muscle during electrical stimulation

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