You’ve probably seen the late-night infomercials from the 90s. A guy with shredded abs sits on a couch, eating pizza, while a little device with sticky pads does all the "work" for him. It looks like magic. It looks like a cheat code. But if you’re asking do TENS units build muscle, I have to be the bearer of some slightly boring news: you probably can't zap your way into a bodybuilding trophy while watching Netflix.
It’s a common mix-up. People see wires and sticky pads and assume all electrical stimulation is the same thing. It’s not. There is a massive, fundamental difference between a TENS unit and an EMS unit, and getting them confused is why so many people end up disappointed with their purchase. If you’re trying to grow your biceps or strengthen a weak quad after surgery, you’re looking at two totally different technologies that speak two different languages to your body.
The science of why TENS isn't for gains
TENS stands for Transcutaneous Electrical Nerve Stimulation. Note that middle word: Nerve.
The entire design of a TENS machine is focused on sensory nerves. It’s a gatekeeper. According to the "Gate Control Theory" of pain—pioneered by Ronald Melzack and Patrick Wall back in the 60s—your spinal cord can only process so many signals at once. By sending a buzzing, tingling sensation through your skin, TENS effectively "clutches" the gate shut so the pain signals from your injury can’t reach your brain. It’s a distraction. A very effective, drug-free distraction, but a distraction nonetheless.
Muscle growth, or hypertrophy, requires something else entirely. It requires tension. It requires the actual shortening and lengthening of muscle fibers under load. A TENS unit typically uses a low milliampere current and a specific pulse width that just isn't powerful enough to cause a motor response. Basically, it tickles the nerves but leaves the muscles sleeping.
If you turn a TENS unit up high enough to make a muscle twitch, it’s usually just painful and chaotic. It’s not the rhythmic, deep contraction needed for protein synthesis.
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EMS is the cousin you’re actually looking for
If you want to talk about muscle, you have to talk about Electrical Muscle Stimulation (EMS). While TENS targets the sensory nerves to stop pain, EMS targets the motor nerves to force a contraction.
Think of it like this. TENS is a whisper to your brain saying "ignore the pain." EMS is a drill sergeant screaming at your muscle to "get to work."
In clinical settings, doctors use EMS—often called NMES (Neuromuscular Electrical Stimulation)—to prevent muscle atrophy. If you’ve had ACL surgery and your quad has "gone to sleep" because you can't put weight on it, EMS can force that muscle to fire so it doesn't wither away. But even then, researchers like those in a study published in the Journal of Applied Physiology have found that while EMS can maintain muscle mass, it rarely outperforms traditional weightlifting for building new, "high-performance" muscle in healthy people.
Why do TENS units build muscle is such a persistent myth?
Marketing. Honestly, that’s the biggest reason.
Companies often sell "combo units" that feature both TENS and EMS modes. Because "TENS" is the more famous acronym, people use it as a catch-all term. You’ll see a listing on Amazon titled "TENS Unit for Muscle Growth," but if you read the fine print, the device actually has an EMS setting.
Another reason for the confusion is the "pump." When you use electrical stim, blood rushes to the area. Your muscles might look a little fuller or tighter for an hour after the session. You feel like you’ve done something. But that’s just localized blood flow and maybe a bit of acute edema (swelling). It isn’t permanent tissue growth.
We also have to look at the placebo effect. When you’re in less pain because the TENS unit is working, you move more. If your back feels better, you might finally go back to the gym and squat. In that roundabout way, the TENS unit helped you build muscle, but it didn't do the lifting for you. It just cleared the path.
The intensity problem
To build muscle, you need to recruit "High-Threshold Motor Units." These are the muscle fibers that only come out to play when things get heavy.
- Walking uses low-threshold fibers.
- Lifting a heavy suitcase uses high-threshold fibers.
- A TENS unit barely touches the low-threshold ones.
Even high-end EMS devices struggle to recruit fibers in a natural way. When you lift a weight, your brain recruits fibers in a specific order (Henneman's Size Principle). Electrical stim recruits them non-selectively and all at once. It’s exhausting for the muscle, but it doesn’t create the same structural adaptations as a barbell.
Real-world applications: When should you actually use TENS?
So, if it’s not for getting jacked, why own one?
I’ve used TENS for years to manage chronic lower back tension. It’s a godsend for that. If you have "office chair back" or a nagging repetitive strain injury, the TENS unit is your best friend. It’s great for:
- Period cramps: Many women find TENS to be more effective than ibuprofen for dysmenorrhea.
- Post-workout soreness: It won't build the muscle, but it might help you manage the DOMS (Delayed Onset Muscle Soreness) so you can train again sooner.
- Arthritis: It’s a staple in physical therapy for managing joint-related nerve pain.
But if your goal is a bigger chest or faster sprints, keep your money in your pocket. Or better yet, buy a kettlebell.
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Nuance in the data: Can stim help anyone build muscle?
There is one specific group where "zapping" actually helps with size: the elderly or the severely immobilized.
A 2014 study involving sedentary older adults showed that consistent use of EMS (not TENS) helped improve leg strength and muscle thickness. When you're starting from a baseline of near-zero activity, any stimulus is better than none. But for a 25-year-old athlete? The stimulus from a battery-powered puck is a drop in the ocean.
There is also some emerging evidence regarding "Concurrent Stimulation." This is where you wear an EMS unit while doing lunges or squats. Some pro athletes use "Compex" units to add an extra layer of difficulty to their bodyweight movements. It’s intense. It’s uncomfortable. And it’s definitely not the "sit on the couch" experience people hope for.
What about the "Ab Belts"?
Most "ab belts" are cheap EMS devices. They can make your abdominal wall feel "tight," and they might even strengthen the muscle slightly if you’ve never done a sit-up in your life. But they will never, ever reveal a six-pack.
Abs are revealed by low body fat. No amount of electrical current can "spot reduce" fat off your stomach. You could have the strongest abs in the world thanks to an EMS belt, but if they’re covered by a layer of adipose tissue, you'll never see them.
Actionable steps for your recovery and growth
If you’re staring at a TENS unit in your shopping cart, here is how you should actually proceed based on your goals.
If you are in pain:
Buy the TENS unit. Look for one with at least 2 channels (4 pads) so you can cross the signals over the painful area. Brands like TENS 7000 are industry standards because they’re analog, durable, and punch way above their weight class in terms of power.
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If you are rehabbing an injury:
Talk to a physical therapist about NMES (EMS). Don't try to DIY muscle re-education. You need specific electrode placement to hit the motor points of the muscle, or you’re just wasting batteries.
If you want to build muscle:
Put the TENS unit away. Focus on the big three:
- Mechanical Tension: Lift heavy stuff.
- Metabolic Stress: Get a "pump" through higher reps.
- Progressive Overload: Do more this week than you did last week.
The "Hybrid" Approach:
If you already own a device that has an EMS mode, try using it during your cool-down. Set it to a low-frequency "thumping" setting. This can act as a form of "active recovery" by flushing the muscle with blood without adding more stress to your central nervous system.
Ultimately, TENS is a tool for comfort, not a tool for construction. It’s the "mute" button for your pain, while actual training is the "volume" knob for your strength. Use them accordingly.
To get started, if you already have a device, check the manual to see if it lists "EMS" or "NMES" specifically. If it only says "TENS," stop trying to use it for calf raises—you’re just giving yourself a weird, tingly sensation for no reason. Instead, use it on your traps after a long day at the computer and enjoy the relief.