How BTS Got So Swole, According to an Expert Trainer#

With enough album sales and Spotify streams to earn K-pop megagroup BTS a spot in the Guinness World Records Hall of Fame, it’s hard to imagine how the record-breaking collective could get any bigger than they already are. But since recently returning from completing their mandatory military service in South Korea, it seems they’ve found a way to do just that.

In a YouTube vlog posted this week by the group’s personal trainer, Ma Sun Ho, we get a glimpse into how the group has been training—and an opportunity to figure out how its members got, well, extremely swole.

To lead our exercise in fast-turnaround fitness forensics, we enlisted the expertise of celebrity trainer Kirk Myers, the founder of A-List sweat spot Dogpound and a man with no shortage of experience training mega-stars like Tom Holland, Jacob Elordi, Patrick Schwarzenegger, and, oh yes, Taylor Swift.

With Myers’ help, here’s everything we learned from BTS’ workout—and how you can use it to pack on a few pounds of muscle of your own.

Lift until you can’t#

In the video, we see the BTS members battling their way through seemingly endless reps of dumbbell hammer curls in L.A.. (At one point, bandmate V asks if anybody is even counting for him.) Rather than aiming for a specific rep count, they appear to be training to failure, which “will help stimulate muscle growth,” says Myers.

A study published in the journal Medicina Sportiva found that training to, or near, failure activates what scientists call “mechanical tension”—a significant driver of muscle growth. You can identify mechanical tension by the natural slowing of reps as your muscles fatigue. Trainers call these “effective reps.”

And even when the BTS members can’t manage one more rep, Ho keeps the set going, helping to lightly nudge the dumbbells up. “Not only are they going to failure, but they’re doing what's called ‘forced reps,’” Myers says. “That's another technique that can stimulate greater muscle growth, and it can also help you break through plateaus.”

Kill the momentum#

At one point, Ho instructs V, who is repping out curls, to pause briefly at the top and bottom of each rep, effectively killing any rebound or momentum. “What I think they're doing a great job of is the movements they're doing are slow and controlled,” says Myers. “That's a very effective way to train—and super effective for gains.”

“If you're swinging the dumbbell up and down, you're not necessarily allowing your biceps to activate fully,” Myers says. “You're probably using some of your front delts, along with momentum from the rest of your body, to move that weight.”

Moving weight with intention also helps you focus on the mind-muscle connection, which can in turn lead to bigger gains, Myers says. Research published in the European Journal of Applied Physiology found that when subjects focused intently on their triceps during heavy bench presses, they were able to increase muscle activation.

Rage with the machines#

Throughout the video, we see the bandmates working out using a pretty even mix of free weights and machines.

Free-weight purists will maintain that dumbbells and barbells are better at recruiting stabilizer muscles and therefore activating more muscle tissue overall, and they’re right. But machines provide a more direct path to muscle growth, by way of mostly removing those supporting muscles from the equation and shifting the bulk of the load onto your primary movers. “Machines help to keep your form in check, and you can really laser-focus on the muscle you're trying to target,” says Myers.

So, the best course, according to Myers, is to do both. And it seems like this is the philosophy Ho is following with BTS. “When they’re doing abs, one of them is doing knee-ups in the Roman chair, while another is laying down and doing crunches in a machine,” says Myers. “I think they're doing a really good job of mixing it up and hitting the muscles from different angles, which is just going to stimulate more hypertrophy, or muscle growth.”

Slow your negatives#

During shoulder exercises like barbell military presses and dumbbell lateral raises, you’ll notice the BTS crew going extra slow on the eccentric portion of their reps. In other words, they’re lowering the weights slowly, rather than just letting gravity do the work.

In a study review published in the Journal of Functional Morphology and Kinesiology, researchers observed that emphasizing the eccentric (also known as negative) phase of each rep can help spur muscle strength and size gains.

“It’s a great way to do hypertrophy training,” says Myers. “If you're able to control the negative, you're just making the movement more effective, as opposed to driving the weight up and dropping it down.”

Play with range of motion#

Early on in the workout, we see bandmate Jung Kook doing dumbbell lateral raises. But instead of stopping when his arms are parallel with the floor, as the exercise is typically performed, he continues to raise the dumbbells until they are all the way overhead. Later, when the gang is doing dumbbell hammer curls, Ho instructs V to effectively cut his range of motion in half, lifting the weights only until his elbow reaches a 90-degree bend.

“It's kind of the theory behind doing 21s,” says Myers, referencing the old-school bodybuilding exercise where you do a 21-rep set of biceps curls, focusing on the lower range of motion for the first seven reps, the upper range for the next seven, and then the full range for the remainder. “It’s just about doing a familiar movement differently, and hitting it from different angles,” he says.

As for the extra range on the lateral raises, “some people would probably say that's harder on your shoulders and you could get injured, but I'm sure there's a reason they’re doing it, especially if you don’t have any shoulder injuries and you can do that full range of motion,” Myers says. After all, Arnold Schwarzenegger famously took his shoulder raises all the way up, too.

Get the band together#

“I also think it's great that they're working out as a group,” says Myers, who encourages people to train with a workout buddy (or six) whenever possible.

In fact, in a recent study published in the journal Management Science, participants who worked out with a partner ended up hitting the gym 35 percent more frequently than those who went alone, even when both groups were incentivized with a cash reward for each visit.

“It just adds that accountability, and it also makes it fun,” Myers says. “[Watching this video], it looks like they're having a lot of fun.”