I zapped my muscles to get swole and it sort of worked

Whether or not you’ve resolved to get into shape this January, Muscle Month is here to teach you a thing or two about stretching, contracting, lifting, tearing, gaining, and so much more.

"I can't believe we woke up at 7 a.m. to pay all this money to get zapped with electricity," isn't something you usually hear from your workout buddy, but the girl next to me wasn't wrong. I'd actually woken up at 6 a.m. to get zapped because we all have our cross to bear. After a year of following a regular and relatively intense weightlifting regimen, I'd been offered a chance to try an Electro Muscle Stimulation (EMS) workout at Shock Therapy, the first U.S. gym to present it in a group setting.

I’d seen the trendy method, oft cited by its disciples as a super-effective fitness trick Europeans have long relied on, all over my Instagram feed, so I decided to give it a try. I would go twice a week for four to six weeks, I told the gym, so I could compare it to my usual four-plus-days-a-week lifting routine and weekend roller derby.

I did not make it to six weeks. But I can't say I totally hated it. Here's what I learned.

Muscles move because brains send electrical signals telling them to do so, and you can hijack this process by using external shocks to trigger movement. If you’ve ever used a TENS unit to manage pain at home or with the help of a physical therapist, you know what the proprietary pads one must wear during an EMS workout feels like. The machine stimulates your muscles to make them prickle and twitch, sometimes to the point of discomfort. If you’ve never used a TENS unit, well, there isn’t really anything else like it—so just imagine your muscles prickling and twitching, sometimes to the point of discomfort.

Proprietors claim that by wearing a suit full of these electrodes (and what basically amounts to a giant soggy wetsuit on top, which is … interesting) you can burn more fat and build more muscle simply because your muscles are doing more work. EMS can be used on top of any kind of training, supposedly boosting the intensity and effectiveness of whatever you’re doing. But I didn’t try bench pressing while getting zapped; the group classes I attended were 25-minute bodyweight routines featuring squats, lunges, and other movements.

Personally, I didn't find wearing a soggy wetsuit and buzzing like an Energizer Bunny to be the most pleasant sensation in the world. But it was interesting, and novelty can be a great tool for getting oneself to the gym. It also wasn't particularly painful (yes, you can crank the intensity way up and make your body feel like it's about to snap in half, but you can also do that with weights). And it was definitely intense: I felt like I'd worked out after just 25 minutes of not moving all that much, which I'm sure is appealing if you're short on time and hungry for results. It mostly just felt like I was doing everything while strapped to super-tight resistance bands perfectly placed to hold back each movement—just with a lot more twitching.

But EMS really confused my body, which is why I only ended up attending four classes. My muscles would keep randomly twitching for a day or two after each session (this one tiny guy in my left glute was especially rambunctious). This phenomenon is touted as making the workout continue on into the next day, but I found it was interfering with my stability on roller skates.

However, this is not to say I was on the whole significantly less stable or able to go about daily life than I am after an intense workout with weights. So if you're not participating in hobbies that involve contact while balancing on four-wheeled death machines, it's probably not going to throw off your groove too much.

“There are these micro-contractions you don’t feel because they’re so fast,” says Esra Cavusoglu, the founder of Shock Therapy Fitness in New York City. “There’s something like 30,000 happening, and these contractions of both slow and fast twitching muscles are fired in a random order.”

Your body builds muscle as it repairs damaged muscle fibers, which is why lifting progressively heavier weights (while eating plenty of calories and giving yourself recovery days) will lead to growth. Cavusoglu, a psychologist from Turkey who first tried EMS while on vacation several years ago, claims that the big difference the method offers is its stimulation of fast-twitch muscle fibers, which are sources of big bursts of power that don't otherwise activate right away.

Greg Nuckols, who holds both degrees in exercise science and three all-time world records in powerlifting, says there is some evidence that EMS can wake up fast-twitch motor units (which refers to a single motor neuron and the muscle fibers it contacts). In a typical workout, your nervous system starts by activating the smallest motor units, which are made of slow-twitch fibers, and works up to the largest, which are fast-twitch, only as muscles contract harder and harder. Light exercise might never stimulate those fast-twitch fibers.

“With EMS, that order may be reversed, or at the very least, a larger proportion of the fibers stimulated during relatively low-force contractions are fast-twitch fibers,” Nuckols explains. So if you curl your bicep up while holding a five-pound weight, as we did in my Shock Therapy classes, you’re probably stimulating your fast-twitch fibers much more with an EMS suit on than without. Fast-twitch muscles have more growth potential, so their activation can really help you bulk up. On the other hand, Nuckols says, you could just do those bicep curls for more reps, or with a heavier weight, and all those same fibers would eventually activate.

Companies imply that using EMS makes you build more muscle and burn more fat, but Nuckols is skeptical. “Burning fat depends primarily on the total caloric expenditure, not the type of muscle fibers recruited,” he says. So if an EMS workout is just way more intense than what you’d otherwise talk yourself into at the gym, you could indeed burn more fat—but there’s nothing magical about electrical pulses.

“At the end of the day, any training method works by creating sufficient muscular tension and inducing a sufficient level of fatigue,” Nuckols says. “That stimulus could come from electrical signals transmitted by your motor neurons to cause voluntary muscle contractions, or from an external electrical source that causes involuntary contractions. So, at least as far as strength and muscle growth go, it works in basically the same way normal resistance training does.”

EMS gyms cite scientific studies and focus groups with truly incredible results, but the method isn't necessarily miraculous. Francisco J. Amaro Gahete, a biomedical Ph.D. student at the University of Granada in Spain, was skeptical of the technology back when he first encountered it as a personal trainer. Now, after several years of research, he sings its praises—with a few caveats.

His research suggests that if a trainer creates an individualized and periodized (meaning it changes at regular intervals to give your body new challenges, while still providing adequate rest) workout incorporating EMS, it can be more effective than similar conditioning without. “Our results strongly support that [EMS] training must be carefully designed and supervised, not only for safety reasons but also for efficiency issues,” says Amaro Gahete.

When tailored precisely to your training needs, it’s easy to see how EMS could help. Cavusoglu references athletes like Usain Bolt, who sometimes uses EMS while running on treadmills to increase his speed when unencumbered. “When you’re running or boxing with the suit it’s almost like you’re pulled by elastic bands,” she says. If nothing else, it indisputably cranks up the intensity of whatever you’re doing—but again, assuming you’re not training for anything as specialized as an Olympic race, you could always just pick a more intense activity and save a few bucks.

"Athletes and strength and conditioning coaches have been experimenting with EMS for decades now, but it's still not very popular," Nuckols says. Based on his examination of the available research, he feels too much of the data comes from studies funded by companies with skin in the EMS game, while even more of it comes from small, imperfect studies impossible to generalize across the broader population. One meta-analysis of all the available research concluded that EMS is an effective form of exercise, but not necessarily a superlative one. Nuckols agrees that its true results are probably more modest than the most impressive studies would suggest. "If EMS actually produced gains that striking, everybody and their brother would be using it."

EMS is not a secret sauce that will turn any couch potato into a bodybuilder in 20 minutes or less, or even a clandestine condiment that will rocket an amateur bodybuilder to the next level; it’s just one more way to make a hard workout harder, and you still need to tailor those workouts to your body and its needs. To me, doing a workout that would be easy if not for the twitching of my muscles was more frustrating than satisfying. If I tried it with heavier weights, it probably would have been too difficult—but yes, it would have sped up my gains!

The biggest potential danger (other than mysteriously twitchy glutes) is rhabdomyolysis—a condition where you inflict so much muscle damage that your kidneys can’t keep up. This is a serious concern, but the risk isn’t necessarily higher with EMS than it is with other forms of intense training (spin classes and CrossFit sessions are also culprits). The reason EMS might warrant particular caution is that people might crank the intensity of the electrical stimulation up way higher than their bodies can handle. You might know full well that doing a bicep curl with a 40-pound weight will overtax your body and get you into trouble, but the unfamiliar sensation of an EMS suit in overdrive might not set off the same alarm bells. That’s why it’s especially important to work one-on-one with a trainer or attend a group gym that pays close attention to your progress.

This hopefully goes without saying, but you also need to make sure you're not just hurting yourself. I have a history of back problems and a very tense upper back, so while I could tolerate a really high EMS setting elsewhere on my body, anything but the lightest electrical pulse between my shoulders made me feel really messed up the next day. The trainers at Shock Therapy took my word for it and never pressured me to turn up the settings on my upper back. But while warning signs of injury are hard to ignore when I'm holding a heavy weight over my head—no one wants a dumbbell to the face—it was way more tempting to try to push through when my only resistance came from a buzzing suit.

If you’ve got the money (it’s expensive—Shock Therapy charges $55 a class) and want to try something new, EMS is a fun alternative to more traditional forms of resistance training. It’s not a way to leapfrog into the body you’ve always dreamed off, but it’s an interesting way to make whatever you’re doing in the gym even harder, and perhaps even a bit more effective.

There is one particular use case I can recommend EMS for wholeheartedly: if you want your muscles to look particularly big and defined for a short period of time. I don't know why you'd want that and I don't care; maybe you're competing or modeling or just want to look swole AF in your wedding dress (same). But when I looked in the mirror for the hour or two following an EMS session, I was like, "OK, but whose arms are those?" And it was great.

“When your muscles contract, that contraction can cut off venous blood flow, which allows fluid and metabolites to accumulate in the limb being exercised,” Nuckols explains. “Since EMS can keep your muscles contracting, your muscles can cut off venous blood flow, which can lead to some gnarly pumps.”

The pumps, my dudes, were indeed gnarly.