Can Zapping Your Muscles Enhance Strength Training?

My first lesson in electrical muscle stimulation (EMS) is this: it won’t work if you’re not wet.

That’s how I found myself, on a Friday afternoon, swapping my gym clothes for a skintight shirt. Personal trainer Connie Ruiz then buckled me into a soft-shell carbon-fiber jacket and matching shorts, each equipped with electrodes. The layers were presoaked, but for good measure, Ruiz fired off a few more squirts of lukewarm water into both the jacket and shorts.

Ruiz is the owner and operator of Personal20, an exercise studio just outside Washington, D.C., that specializes in one-on-one EMS training. Ruiz guides everyone from gym novices to fitness junkies through 20-minute strength workouts while delivering low-frequency currents to their muscles via an E-Fit muscle-stimulation machine: a metal box with an LCD, ten dials, and two leads that are attached to the jacket and shorts I’m wearing. Twisting the dials sends electricity to different muscle groups.

According to James Cousler, a certified strength and conditioning specialist and Personal20’s director of education, slow-twitch muscle fibers are usually the first to be engaged during a strength workout. Engaging the fast-twitch fibers, he says, requires more resistance. EMS training is more time-efficient: it activates both types of fibers simultaneously, without the additional load. Proponents of EMS say that this leads to a harder workout in a fraction of the time—one that works the muscles and defines them without putting as much stress on the joints. Ruiz discovered EMS exercise five years ago, tried it for a month, and never looked back. “I couldn’t believe the definition I started seeing in my arms,” she says.

Physical therapists and elite athletes have used EMS as a recovery tool for decades. Some research shows that electrically induced muscle contractions may reduce swelling, inflammation, and pain. By the early 2000s, EMS became more popular among the fitness crowd, who zapped their muscles on a hunch that being jolted with electricity would increase their gains. In the past several years, EMS workout studios have popped up in New York, Tennessee, Florida, and a handful of other states, including Ruiz’s studio in Virginia, where three introductory sessions will run you $109.

There’s a small but growing body of research assessing the effectiveness of EMS for strength training. A 2016 study with 41 participants, for example, showed that EMS workouts were roughly as effective as high-­intensity resistance training in increasing muscle gains. (Unsurprisingly, in addition to being peddled to the fitness crowd, EMS is also advertised as a hassle-free way to tone abs and tighten butts. One such product, the Flex Belt, has been cleared by the Food and Drug Administration for strengthening abdominal muscles.) But standing there dressed like an extra from Tron, I was pretty skeptical.

Ruiz started by determining my optimal electrical setting (a medium level, which she said was normal for a newbie); I immediately felt the throbs in my thighs. She let it run during a warm-up round of bodyweight squats and jumping jacks, then eventually handed me a pair of two-pound weights and told me to do ten biceps curls. I thought she was joking, but by the eighth rep my arms felt it. After kickbacks, rows, and flys, my muscles were tight—the type of tightness I’d feel after doing the same exercises with 40-pound dumbbells—and pulsing intermittently as Ruiz adjusted the machine’s dials.

Critics question whether EMS is really better than regular strength training, and a 2019 review of research was inconclusive on the effectiveness of EMS workouts. Meanwhile, the Food and Drug Administration notes that while EMS devices can speed recovery and may be able to strengthen muscles, they’re not a shortcut to a six-pack.

Close to the end of our 20-minute session, though, I was feeling the EMS’s power. Sets of crunches and planks had my core shaking, partly from the electrical current and partly from fatigue. For the cooldown, Ruiz had me lie on my back on a floor mat. “We call this the fish flopping out of water,” she said. While I relaxed with light current jostling my arms and legs, I felt soggy, sore, and surprisingly satisfied. Even if it’s no better than lifting, it’s certainly less boring than your average trip to the gym.