The 3 hardest Olympics sports, according to sports medicine experts

Insider asked sports medicine pros to name the hardest Olympic sports - physically, technically, mentally. Water sports and acrobatics came up most.

• Insider asked six sports medicine professionals to name the hardest summer Olympic sports.
• They considered the physical, technical, and mental strength needed.
• Water polo came up on top, followed by gymnastics and swimming.
• Visit Insider's homepage for more stories.

What's the hardest summer Olympic sport? That question is just as much up for debate as the answer.

"What's harder?" Dr. Rand McClain, chief medical officer of LCR Health who treats elite and amateur athletes, rhetorically asked Insider.

"Holding your breath under water while pushing most of your lower body above water? Continuing to bicycle right at your anaerobic threshold for as long as possible? Standing opposite an opponent who just hit you squarely in the jaw ... in fear of being permanently injured or dying?"

At the Olympic level, it's all superhuman-level hard. But a few sports stand out as the most difficult of them all.

Insider asked six sports medicine professionals to name the toughest sports we'll see in Tokyo based on the physical, technical, and mental strength needed.

Water polo was named the most physically strenuous Olympic sport

Water polo often tops lists of most difficult sports. In 2016, Bleacher Report declared it to be "the toughest sport in the world" based on six parameters: strength, endurance, speed, agility, skill, and physicality.

On top of treading water for 30 minutes and swimming up to a mile per game, athletes "sneak in blows to each other similar to ice hockey and soccer, while trying to not touch the ground, not drown, and score points all at the same time," Nandini Collins, a trainer and exercise physiologist who works at Noom, told Insider. "Water polo is played with reckless abandon and is more violent than spectators assume."

Dr. Naresh Rao, the US men's water polohead physician for the Men's USA Water Polo team, told Insider water polo is strenuous because it requires both aerobic (used for endurance) and anaerobic (used for sprints) capacity.

McClain was unequivocal about his vote for water polo: It's "the 'hardest' summer Olympic sport," he said. "Why? It requires the highest VO2 max of any of them." However, the data on that theory is mixed, with many top swimmers, distance runners, and cyclists all having exceptional VO2 maxes, or a measure of how efficiently your body exchanges oxygen.

Gymnastics won the most points for technical and mental strength

Four of the seven experts named gymastics the most demanding sport in at least one of the categories: physical, technical, and mental strength.

"There is a high level of risk with the elements, and gymnasts are required to master balance, strength, flexibility, and endurance of both upper and lower extremities in order to achieve Olympic-level greatness, Dr. Kathleen Davenport, the director of Physiatry HSS Florida who works with dancers, told Insider.

They also need "power and explosiveness" Nandini said. And mentally, Davenport added, they need "an extreme level of focus" to perform dangerous stunts - even after a crushing fall.

A few other sports took bronze

Swimming earned one vote for overall toughness and another for mental strength, since it's a "sensory deprivation sport," HHS's Dr. Tate Greditzer, a former professional water polo player, told Insider.

Boxers, decathletes, and 800-meter sprinters each got a vote as the most physically challenging sport.

In the 800, "runners literally have to run at 90% of their full speed for well under two minutes," trainer Jon P of Stop Crying Studios told Insider. The one time he ran it, he felt "complete numbness, inside and out" afterwards. "My vision blurred, I couldn't catch my breath, or gather enough oxygen to stand upright for a while," he said.

Surfing and pole vault each got a vote for the most technically difficult sport.

For mental strength, tennis, and the marathon earned a vote, though all Olympians are exceptional in that department, Dr. Kevin Bernstein, the chief medical officer at Peaks Coaching Group, told Insider.

"Most of those that lack mental strength do not get this far solely with raw physical talent, regardless of sport."