DENVER >> Joking around before the start of the NBA Finals, Charles Barkley and Grant Hill took hits from oxygen masks they brought onto the set for a pregame TV show.

But the thin air in Denver is no joke. There’s a reason it’s known as the Mile High City.

The city sits 5,280 feet above sea level and there’s plenty of science that shows just how altitude impacts any athlete — including basketball players. The Denver Nuggets have been using the lung-searing elevation to their advantage for years — especially during these playoffs.

With their 104-93 win over the Miami Heat on Thursday, the Nuggets improved to 9-0 at home during their postseason run. Yes, Nikola Jokic, Jamal Murray and friends have a lot to do with it. But altitude deserves an assist. The Nuggets try to push the pace to make the Heat feel the burn coming in from sea level.

“So there’s just as much as oxygen in Denver as there is in Miami,” explained Randy Wilber, a senior sports physiologist for the U.S. Olympic & Paralympic Committee. “What’s different is the barometric pressure in Denver is significantly lower than in Miami. … So ultimately, yes, you’re getting less oxygen to your working muscles.

“That’s a fact. That’s not a wives’ tale. That’s not a myth.”

The Nuggets know it. And they remind opponents of it. There’s a sign that greets visiting teams entering Ball Arena listing the elevation. Before games, the stadium announcer proclaims the challenges of playing at altitude. On the floor, “5280” is stenciled at each free throw line — just to provide another reminder.

The Heat, though, aren’t letting it get into their heads.

“I don’t think that was part of the game,” Heat center Bam Adebayo said of the role of elevation after Game 1. “I didn’t even think about the altitude until you just said it.”

To the Heat, the adjustments for Game 2 on Sunday night have more to do with shot making than altitude concerns. The Miami trio of Caleb Martin, Max Strus and Duncan Robinson went a combined 2 for 23 from the floor.

The Heat have shown they can soar at elevation.

Miami beat San Antonio in December in Mexico City, where the altitude is 7,350 feet above sea level. Heat guard Jimmy Butler even found a unique strategy that seemed to work: Eating grasshoppers, a local delicacy, along with drinking some tequila.

It worked so well for him in Mexico City — he had 26 points — he floated a similar plan in Denver.

“You’ve just got to listen to music, drink water, drink wine, play Spades (a card game) and dominoes,” Butler said before the series.

While the Nuggets players are obviously more comfortable playing in the thin air, they aren’t immune to the effects of altitude. Reserve Bruce Brown said he experienced cramps in Game 1.

“You’ve got to get used to the altitude,” Brown said.

Getting acclimated to the elevation typically takes about five days for an elite athlete, Wilber said.

Theoretically, it should put the Heat on schedule for Sunday’s game. That’s if they are adhering to a specific checklist, which includes hydrating, plenty of sleep and even more hydrating.

Wilber has been studying the effects of environmental physiology — heat, humidity, altitude — for the better part of 30 years. Once an 800-meter runner, he’s long been fascinated by the factors that may influence an event.

In his lab — the High Altitude Training Center in Colorado Springs — he and his team can simulate just about anything. That includes “going up the mountain” — his description — to about 20,000 feet and “going down the mountain” to sea level within minutes. The 2,000 square-foot center can accommodate multiple athletes in multiple sports.

“Acclimatization is really just common sense,” said Wilber, who’s authored numerous papers on sport science and fashions game plans for teams to help maximize performance. “It’s just taking on a little bit more every day until you either measure it physiologically or you sense it intuitively that, ‘OK, I feel pretty good. I’m sleeping good. I’m hydrated. I’m ready to ramp up my training load today and see how I do.’

“But you don’t want to do that off the plane.”

To further explain his point, Wilber used the analogy of a hammer. At sea level, the oxygen molecules are driven into the lungs and into the blood with the force of a sledge hammer. In Denver, it’s more like using a ball-peen hammer.

“And ultimately, that means premature fatigue on the basketball court,” Wilber said.

Heat coach Erik Spoelstra has heard it all. But he’s not letting altitude slip into his players’ thoughts.

“Our guys are in great shape,” Spoesltra said. “They’re ready to compete. If Denver wants to tip this thing off at the top of Everest, we’ll do that.”

Spoelsta maintained the Heat have a home-city advantage of their own — humidity.

“We’ll turn off the air conditioning and they’ve got to play in 90-degree humidity,” Spoelstra joked, saying that tactic will sap the energy out of their legs. “This thing is going to be decided between those four lines.”