By Conrad Sanchez - Edits by Janel Leader

If you are an EMS trainer, you may not like to hear this… but "EMS activates 90% of your body’s muscles simultaneously” and “EMS activates 90% of muscle fibers” are nice-sounding benefits, but unfortunately, not exactly true.

It sounds scientific. It features a precise, high number that looks impressive. And yet, it is physiologically incorrect. This blog is not designed to disparage EMS as a training tool. It is my whole business, and an effective tool to get people stronger. For certain populations, EMS is the ideal tool even! 

However, I find the dangers of letting marketing sound bites trump scientific evidence worse than setting the record straight. 

This being said, I could be wrong, and I invite anybody with evidence that WB-EMS does indeed contract 90% of muscle fibers to come forward, and I’ll highlight the findings. 

The Origin of the "90% Myth"

A lot of the benefits and distorted marketing claims for whole body electrical muscle stimulation actually come from localized NMES (neuromuscular electrical stimulation) studies.

In localized, clinical studies, researchers demonstrated that electrical currents can depolarize nerve axons directly beneath an electrode pad in a non-selective, synchronous manner. Some studies observed that, within that specific, localized site, a high percentage of the underlying muscle fibers were activated. Marketers simply took the phrase "90% of fibers under this 2x2 electrode" and warped it into "90% of your total body muscle mass."

Some marketing copy even attempts to rescue this myth by shifting the claim from "total body" to "90% of fibers within a specific muscle." This is still a reach. While NMES can depolarize a high percentage of motor units directly beneath an electrode pad, this does not translate into 90% of the entire muscle contracting with functional force. To reach fibers deep within the muscle belly without damaging the superficial tissue, you would need to exceed the safety and comfort thresholds of human physiology.

The Historical Context: 

The "90% myth" is a direct descendant of the infomercial boom of the early 2000s, where "passive ab belts" promised effortless six-packs. In May 2000, the American Council on Exercise (ACE) debunked these claims, finding that in-home EMS devices did not produce significant changes in strength or body composition. 

Note: Looking more closely at the article and the attached PDF, they also seemed to admit that better EMS devices yielded better results. 

This research was instrumental in the U.S. Federal Trade Commission (FTC) enforcing a major crackdown in 2002 against manufacturers making deceptive claims about muscle activation and effortless caloric expenditure. 

All of these ab-belt manufacturers were claiming that you would get washboard abs by using these devices. This is not how fat-loss works. Fat loss comes from a bigger equation that includes a proper diet, sufficient sleep, adequate stress management, hormonal balance, and exercise.

Physiological Barriers to 90% Muscle Fiber Activation: 

Under normal conditions, our central nervous system operates via Henneman’s Size Principle, recruiting motor units in a sequential order from small, fatigue-resistant fibers to the larger, high-force fibers required for heavier loads.

The true limit of muscle recruitment is defined by our own central nervous system, not by a lack of external stimulus. In foundational research using the "twitch interpolation" technique (the gold standard for measuring voluntary activation), Herbert and Gandevia (1999) demonstrated that the relationship between neural excitation and force output is complex and non-linear. This research underscores that the human brain is already highly efficient at optimizing motor unit recruitment to meet functional demands. Consequently, the idea that an EMS session can "unlock" a massive percentage of dormant muscle fibers, bypassing the sophisticated neural governance your brain has already established, is a misunderstanding of human physiology. We don't use WB-EMS to "fix" a failure in fiber recruitment. We use it as a tool to superimpose an additional metabolic load onto an already optimized neuromuscular system. 

Marketing claiming "90% fiber recruitment" is bending reality a bit: 

1. The Depth-Intensity Wall: Electrical current follows the path of least resistance, which is concentrated at the skin and superficial tissue. To reach the deep-seated fibers near the bone, you would need to push the current to a level that induces severe pain, skin irritation, and autonomic distress long before the deep motor units are ever engaged.

Gregory, C. M., & Bickel, C. S. (2005). Recruitment patterns in human skeletal muscle during electrical stimulation. The authors explicitly note that electrical stimulation is spatially limited. They explain that the distribution of current is non-uniform and biased toward the superficial motor units located closest to the electrode. Increasing intensity to reach deeper tissue inevitably activates superficial nociceptors (pain fibers) long before full muscle depth is recruited.

2. Non-Selective Stimulation: Unlike the nervous system, which is inherently "selective" and task-oriented, NMES is non-selective. It fires whatever is close to the electrode, regardless of the muscle’s functional need. It cannot "search out" the deepest 10-20% of fibers in a muscle belly. In my opinion, this is a point in favor of using relatively heavy weights along with EMS.

Maffiuletti, N. A. (2010). Physiological and methodological considerations for the use of neuromuscular electrical stimulation. Maffiuletti highlights that while voluntary contractions are selective and tailored to the task (e.g., endurance vs. power), EMS recruitment is "non-selective." It cannot distinguish between fiber types or depths. EMS hits whatever is in the path of the current, which is mostly superficial. 

This shouldn’t be misinterpreted as not being effective. WB-EMS still remains a very effective method for getting people stronger.

3. Depolarization ≠ Functional Recruitment: Marketing often confuses depolarizing a neuron with the result of functional recruitment. Even when an electrode successfully triggers a high number of fibers, the resulting contraction is synchronous, meaning every single recruited fiber fires at the same time. This creates a massive, high-tension spike that is metabolically exhausting, but it is a far cry from 90% of a muscle’s contractile capacity working in a coordinated, functional, or efficient manner.

Bergquist, A. J., et al. (2011). Motor unit recruitment when neuromuscular electrical stimulation is applied to human muscle. This paper details the limitations of NMES in producing functional, coordinated force. It establishes that because NMES causes synchronous firing (all units firing at once), it leads to premature fatigue and a loss of the precise, graded force production required for functional human movement. It distinguishes between the "electrical twitch" (the depolarization) and the "functional output" (the force generation).

Gondin, J., et al. (2005). Electromyostimulation training effects on neural drive and muscle architecture. This study provides a guide for how EMS alters neural drive, highlighting its role in muscle adaptation without the myths of total-body activation. 

Synchronous vs. Asynchronous: Voluntary movement is asynchronous. Your central nervous system regulates motor unit recruitment to maintain smooth, sustainable, and coordinated force. NMES is synchronous. It forces every recruited unit to fire simultaneously. While this synchronous firing is the mechanism behind a fused tetanic contraction, it is also the reason why 90% recruitment via EMS is impractical.

If 90% of a muscle’s fibers were forced into a fused, synchronous state, the metabolic demand and tension would be so extreme that it would trigger immediate failure. This is why WB-EMS uses frequency modulation and duty cycles to provide an effective stimulus without forcing the muscle into the kind of uncontrollable, exhaustive state that true 90% synchronous recruitment would require.

Can humans recruit 90% of their muscle fibers? Sure, your brain is already capable of that during a max effort lift, but it does so asynchronously to manage the load. WB-EMS does not mimic that 90% state. Instead, it adds a high-density, synchronous load that complements your voluntary effort, helping you hit your training goals more efficiently.

What to Tell Your Clients Instead

In my opinion, WB-EMS is a technology that requires science to explain how it works. We do not need to rely on myths to sell the efficacy of WB-EMS. When we combine WB-EMS with weight training, we are superimposing an external, synchronous stimulus on top of an asynchronous voluntary contraction.

Marketing-Friendly (But Scientifically Accurate) Sound Bites

On Efficiency & Time

• "High-density training: Achieve a full-body stimulus in just 20 minutes through simultaneous muscle group recruitment."
• "Access high-threshold muscle fibers immediately, without the need for hours of traditional lifting."
• "Efficiency by design: A complete metabolic load in 20 minutes, superimposing electrical assistance onto every movement."

On Type II Fiber Recruitment (The "Fast-Twitch" Benefit)

• "Engage high-threshold Type II muscle fibers from your very first session, regardless of current strength levels."
• "Train your fast-twitch fibers: Utilize electrical assistance to reach peak muscle potential that traditional low-load training often ignores."
• “Get strong faster”
• "Activate strength and power muscle fibers on command, utilizing electrical stimulation to accelerate your training response."

On Joint Safety & Accessibility

• "Maximum output, minimum impact: Build strength through intense muscular contraction, without joint stress."
• "Load the muscle, spare the joint."
• "Range-of-motion freedom: Achieve profound muscular activation without requiring the deep, complex movement patterns that can strain vulnerable joints."

On Pain Management & Functional Recovery

• "Targeted pain relief: Utilize rhythmic, electrical contractions to increase local circulation and mitigate chronic aches."
• "Support your recovery: Enhance local metabolic activity and blood flow through controlled electrical assistance, aiding the management of recurring muscle soreness."
• "Functional restoration: Improve muscle tonicity and support pain-free movement through precise, joint-friendly electrical protocols."

The "Superimposition" 

• "The multiplier effect: Superimpose electrical assistance onto your functional movements to amplify time-under-tension beyond what voluntary effort alone can achieve."
• "By combining voluntary movement with electrical stimulation, we create a multi-layered stimulus that drives adaptation more efficiently than either method alone."
• "Dynamic synchronization: Leverage the power of superimposed stimuli to force your muscles to work harder, smarter, and more efficiently."

Just some examples you can use!

I offer in-studio sessions in Beverly Hills, located at 300 S. Beverly Dr., alongside my colleague Janel and co-founder Sarah, who provides private and semi-private Pilates sessions. Find out more here: lamaisonpilatesems.com

If you're interested in at-home EMS training and live near Santa Monica, Brentwood, Palms, Beverly Hills, or Bel-Air, please send me an email at conradfitness@gmail.com or book a 15 min call with me.

If you are looking for an EMS trainer in other cities, please check my trusted network.

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