When dual moguls made its Olympic debut on Saturday, it delivered more than promised. 

A head-to-head run between Japan’s Ikuma Hiroshima and American Nick Page during the men's dual moguls quarterfinals turned into a battle just to stay on their skis as both skiers' lost control and tumbled down the course, with Horishima finishing the race backwards. 

It was the kind of run that makes casual viewers ask the same question moguls skiers have heard for years: how are their knees still intact?

It turns out knees are the least of their worries.

"People definitely always assume the knees," American Jaelin Kauf, who earned silver in women's dual moguls, said. "I personally feel it a lot more in the back than the knees."

Dr. Kelsey Albert, a former U.S. moguls skier turned board-certified physical medicine and rehabilitation physician, confirmed that while ACL tears and acute knee injuries are common, the repetitive compression through the spine can be harder to manage long term. 

"The knees tend to be easy to get surgery on if you need to versus the back is more that the system gets out of whack," she said. "Knee ligament tearing is gradual stretching, and then you have more compression of your back. So [that is] trickier to diagnose. Traditionally, there weren't options to treat those."

The key to moguls is shock absorption. Skiers require a centered stance, applying pressure to the front of their skis rather than the back. A good skier remains in contact with the snow at all times, flexing as they hit the mogul and extending as they descend into the trough. When done right, athletes appear to be pogoing between the rounded mounds of snow, upper body held upright while the knees ping pong back and forth. That feeling athletes are chasing is a rhythm "when it feels effortless," as Albert puts it.

"You can almost think of it as like the suspension on a mountain bike," Albert said. "The goal is to minimize force as much as possible. So, when you're coming up on the mogul, you're trying to absorb that mogul."

Though the focus is usually on the knees, the consistent shock absorption from moguls as well as the strain from high-speed jump landings actually places greater stress on the lumbar spine, resulting in lingering issues in many skiers' lower backs due to repeated impact.

"There's ligaments that hold your disc and vertebrae together," Albert said. "With the repetitive compression in mogul skiing, it's really easy for those ligaments in the back to get stretched. With just normal motion, you have more compression and more overload."

Moguls skiers strengthen their muscles as much as possible to prevent ligament and joint damage. Neuromuscular joint protection, a common strategy to maintain and protect joints through improved muscle control, is commonly practiced by skiers to train their brain to protect their muscles at all times.

"The key thing is you want your muscles firing all the time because the more your muscles are firing and talking to your brain, the less force you have on your joints," Albert said. "If your quads, your hamstrings, your glutes, those are all firing at the right time, there's less force into your knee joint, your ligament, your meniscus."

Training for moguls requires a dynamic approach. It can include anything from single-leg strengthening and balance training, to core workouts and water ramp training in order to minimize risk by limiting time on course. "We do so much strength training and conditioning throughout the winter, throughout the prep season to be able to physically handle what we're doing out there," Kauf said.

Dual moguls adds the additional challenge of racing side-by-side down a course up to 270 meters long. In less than 25 seconds, skiers are expected to expertly navigate a course full of moguls and land a series of aerial tricks all while trying to finish ahead of the skier in the next lane.

"In the singles, they're very controlled, they're doing those motions that they've trained all the time," Albert said. "But when you're side to side next to someone, it pushes them slightly out of that comfort level that they're in. You see them get into a lot more positions where they're putting their body at risk for injury."

The race aspect of the event changes the mentality, Albert explained, as "you're pushing yourself more than you might normally," increasing the risk of the crashes that defined the men's and women's events at these Games. Kauf and teammate Liz Lemley both crashed hard en route to their respective silver and bronze medals in women's dual moguls while Malica Malherbe (RSA), Julien Viel (CAN), and Li Ruilin (CHN) were some of the many others to stumble their way down the course. Despite enduring painful crashes, skiers are conditioned to protect themselves and pop back up for the next race.

"Regardless if you crash, there's a lot of motivation, there's a lot of adrenaline," Lemley said. "You just pick yourself back up, you go up there, and you just do your best that you can."

Lemley and Kauf were the only two American moguls skiers to earn Olympic medals, with Lemley taking home a gold and bronze and Kauf adding two silvers to the silver she claimed four years ago in Beijing. On Saturday's women's dual moguls event, Lemley bested France's Perrine Laffont, 18 to 17, in the small final for her bronze while Kauf fell just short of Jakara Anthony (AUS) in the big final for silver.

"Throughout the day, I was really focused on my starts and my exits from top air as those are the places that you can gain, which I think I did really well," Lemley said. "I was able to edge out a lot of my competitors with those, and I think I nailed that."

At one point, Lemley and Kauf made up a quarter of the U.S.' total medal count at the Games when they claimed their dual moguls medals, holding four Olympic medals of the 12 earned at that time. 

"Going into these Games, [I] expected a couple of U.S. athletes from our women's team to be on the podium every day," Kauf said. "We have such a strong, stacked team. Whether it was Liz and I, or Liv (Olivia Giaccio) and Tess (Tess Johnson), someone from our team was gonna be on the podium."