The Olympic sports with the highest risk of serious injury, from horse-riding to biking

• Simone Biles generated a fresh conversation about how dangerous gymnastics can be.
• But BMX and boxing are rated the most risky since serious injuries are relatively frequent.
• Canoe slalom, rowing, shooting, and archery are among the least dangerous Olympic sports.

When Simone Biles pulled out of several Olympic events due in part to "the twisties" - a disorienting and dangerous phenomenon causing athletes to get lost in the air - viewers confronted an overlooked reality: Gymnastics isn't just captivating and beautiful to watch, it can be life-threatening to the Olympians performing.

"In our sport, we essentially dive into a pool with no water," former Olympic gymnast Dominique Moceano tweeted July 28. "When you lose your ability to find the ground ... the consequences can be catastrophic."

Gymnastics isn't the only Olympic sport with a high level of risk. And, according to a study in the British Journal of Sports Medicine conducted after the Rio Games, it's not even one of the riskiest, since such catastrophic events rarely occur - a true testament to their skill.

Rather, the following sports are considered most dangerous because they relatively frequently cause physical harm.

BMX cyclists are most likely to get injured, followed by boxers

In 2016, 38% of BMX cyclists suffered injuries, compared to 8% of Olympians overall. The sport requires competitors to propel off a hill before riding over jumps and tight corners at as high as 37 miles per hour, according to Olympics.com.

The cyclists wear full-body protective gear because they need it: "BMX racing is essentially a contact sport and onlookers may see riders push and bump each other in the chaos of the race," the Olympics website says.

On Friday, the sport's risk played out in terrifying real time, as American BMX racer Connor Fields caught the wheel of the one racer ahead of him before crashing and bringing two other competitors tumbling down. The 2016 gold medalist was hospitalized with a brain hemorrhage, a broken rib, and a bruised lung, but is no longer in critical care.

Boxing, mountain biking, and taekwondo are the next most-risky sports, according to BMJ, with 30%, 24%, and 24% of Rio athletes injured, respectively. Boxers "not only frequently get cut or incur broken facial bones, but they also often get knocked out, suffer concussions, and even die in the ring," Dr. Rand McClain, chief medical officer of LCR Health who treats elite and amateur athletes, told Insider.

Equestrian is exceptionally dangerous but, fortunately, catastrophes rarely occur

In the 2016 Olympics, less than 5% of equestrian athletes suffered injuries, putting it toward the bottom of the risky list - well behind badminton and handball. But when accidents happen with a 1,200-pound animal galloping, weaving, and jumping more than 20 miles per hour, they can lead to permanent injury or death.

"Any mistake can be extremely dangerous for both the rider and the horse," Dr. Kathleen Davenport the director of Physiatry HSS Florida who works with dancers, told Insider. "These athletes are pushing themselves to their limit together, with often new courses to navigate, and in a high stakes environment."

On Sunday in Tokyo, a Swiss horse was euthanized after suffering an "irreparable ligament rupture" in its leg.

Canoe slalom, shooting, and rowing are among the least risky activities

No Olympians were injured in the canoe slalom in 2016, an event in which athletes navigate an artificial whitewater course while passing through upstream and downstream gates.

Less than 3% of Olympic rowers, shooters, archers, swimmers, golfers, and table tennis players got injured. And such injuries are medically minor, like a nerve issue in a finger or an overuse injury in a golfer.

In contrast to dangerous combat sports, individual in sports like swimming may be exceptionally physically strenuous, but "you are in control of the effort you put forth, and no one is trying to strike you," McClain said.