EMS machines can build muscle, but not as effectively as traditional resistance training. In a 20-week study comparing whole-body EMS to conventional weightlifting, both groups gained strength, but the weightlifting group came out ahead on nearly every measure. EMS is a real training stimulus, not a gimmick, but it has clear limits as a standalone muscle-building tool.
How EMS Forces Muscles to Contract
When you lift a weight, your brain sends signals through your nerves to activate muscle fibers in a specific order. Small, slow-twitch fibers fire first, and your body only calls on bigger, more powerful fast-twitch fibers when the load demands it. This orderly sequencing is how voluntary movement works.
EMS bypasses your brain entirely. Electrodes on your skin send electrical pulses directly into the nerve fibers near the surface, causing involuntary muscle contractions. The recruitment pattern flips: EMS tends to activate larger motor units before smaller ones, essentially reversing the normal order. It also fires many motor units at once rather than staggering them the way your nervous system would. This simultaneous activation is part of why EMS-stimulated muscles fatigue faster than muscles working under voluntary control. Your body isn’t designed to fire everything at once for sustained periods.
What the Strength Numbers Actually Show
A 20-week intervention published in the Journal of Exercise Science and Fitness compared 25-minute EMS sessions to 90-minute full-body resistance training workouts. Both groups started at similar strength levels. Here’s where they ended up:
- Bench press: The EMS group went from about 45 kg to 58 kg. The weightlifting group went from 45 kg to 63 kg.
- Leg press: EMS improved from 121 kg to 148 kg. Weightlifting went from 123 kg to 170 kg.
- Shoulder press: EMS gained roughly 6 kg over the study period. Weightlifting gained about 14 kg.
- Biceps curl: This was the one exercise where the difference between groups wasn’t statistically significant. Both improved by roughly 7 to 10 kg.
The pattern is consistent: EMS produced real strength gains, but traditional resistance training produced substantially more. The gap was largest in compound movements like the leg press and shoulder press, where the ability to progressively load heavier weights gives conventional training a clear advantage. For a time investment of 25 minutes versus 90 minutes, though, EMS delivered a respectable return.
Does EMS Increase Muscle Size?
Strength and muscle size don’t always move together, so it’s worth looking at hypertrophy specifically. The evidence here is thinner but generally positive. A systematic review in the German Journal of Sports Medicine found that EMS training can increase muscle size and reduce body fat percentage compared to control groups. One study within that review showed that adding whole-body EMS to jump training increased the diameter of fast-twitch muscle fibers, something that didn’t happen with jump training alone.
That said, the same review concluded that it’s “inconclusive” whether EMS is as effective as other types of training for muscle mass gains. The muscle growth is real but modest, and it’s unlikely to match what progressive resistance training delivers over the same timeframe.
Where EMS Works Best
EMS shows its strongest advantages in populations where traditional exercise is difficult or impossible. For people recovering from surgery, managing chronic conditions like COPD, or dealing with prolonged bed rest, EMS can help slow or partially prevent muscle wasting. Studies in clinical populations have found small to moderate effects on preserving muscle mass, with some trials showing measurably better muscle preservation compared to no intervention.
For active people, EMS is most useful as a supplement rather than a replacement. Layering EMS on top of voluntary exercise may offer a modest edge because the two methods recruit muscle fibers differently. Your voluntary effort catches the small fibers first and works up; the electrical stimulation hits larger fibers that might not get fully activated during a given exercise. Combined, the muscle gets a broader stimulus than either method alone provides.
Consumer Devices vs. Professional Equipment
The FDA has reviewed and cleared EMS devices primarily for use in physical therapy and rehabilitation under professional supervision. Consumer devices sold for home use must meet the same safety and effectiveness requirements before they can legally be marketed. The FDA specifically notes that while EMS may “temporarily strengthen, tone or firm a muscle,” no devices have been cleared for weight loss, girth reduction, or producing dramatic visible results like “rock hard abs.”
This distinction matters because the intensity required to trigger meaningful muscle adaptation is significantly higher than what most consumer-grade devices deliver. Professional whole-body EMS systems used in supervised training studios can push current through large electrode suits covering your arms, legs, chest, back, and glutes simultaneously. The small pad-style units sold online typically target one or two muscle groups at lower intensities, which limits their muscle-building potential considerably.
Safety Risks to Take Seriously
The most dangerous complication from EMS is rhabdomyolysis, a condition where damaged muscle fibers break down and release their contents into the bloodstream. In severe cases, this can damage the kidneys. A documented case involved a 46-year-old professional athlete who developed both rhabdomyolysis and compartment syndrome after a single high-intensity EMS session. Her creatine kinase levels, a marker of muscle damage, peaked at nearly 29,000 (normal is 40 to 200). She had underlying chronic pain conditions and kidney disease, which increased her risk, but the trainer kept the device at maximum intensity despite her discomfort during the session.
People most at risk include those who are new to EMS, anyone with kidney disease, uncontrolled diabetes, thyroid disorders, or underlying muscle conditions. High-frequency settings cause more muscle damage than lower frequencies. The lesson: start at low intensity and progress gradually, even if you’re already fit. Being an experienced athlete doesn’t protect you if you’ve never used EMS before.
Who Should Avoid EMS Entirely
EMS is contraindicated for anyone with an implanted electronic device, including pacemakers, defibrillators, neurostimulators, or pain pumps. The electrical current can interfere with these devices in unpredictable ways. Other conditions that typically exclude people from EMS use include:
- Pregnancy
- Epilepsy
- Recent heart attack or unstable heart conditions
- Active blood clots (thrombosis)
- Abdominal or groin hernias
- Extensive skin conditions in areas where electrodes would be placed
- Recent cancer surgery (within the past three months)
The Bottom Line on Muscle Building
EMS creates a genuine muscle contraction and a genuine training stimulus. Over weeks and months, it produces measurable gains in both strength and muscle size. But those gains consistently fall short of what you’d get from picking up actual weights. If you can do conventional resistance training, EMS is best used as a complement, not a replacement. If injury, illness, or immobility limits your ability to train normally, EMS becomes a much more valuable tool for maintaining muscle you’d otherwise lose.