There are about three seconds when everyone waits. It’s the momentary pause after practice when Bill Belichick decides whether the Patriots will run up a hill situated next to New England’s practice field. There’s probably some false hope because they almost always run. Running — running a lot, running smarter than anyone else, and running when they do not want to — is one of the Patriots’ secret weapons. It is, players and coaches say, a key reason they have engineered some of the greatest comebacks in football history.

“The fourth quarter. The fourth quarter is exactly what we are thinking about when we’re running,” said Moses Cabrera, the team’s strength and conditioning coach.

The Patriots are, simply put, awesome in the fourth quarter. They have erased a double-digit deficit in four playoff games in the Brady-Belichick era. No other quarterback in history has done that more than once. They erased a 10-point deficit in the fourth quarter in the AFC championship game against the Jacksonville Jaguars and erased a deficit in last year’s Super Bowl that, at the start of the fourth quarter, was 19 points. But this goes beyond the score line: During the Jacksonville game, three of the four fastest Patriots plays happened in the fourth quarter, including Dion Lewis’s fourth-quarter run (17.6 miles per hour) to gain a first down and seal the game. There are many areas in which New England’s supposed edges are overstated; Belichick himself has said that he thinks that “playoff experience” is useless. Superior conditioning, though, is a real, tangible edge. New England’s ability to come back from impossible odds is directly tied to it. In large part, the Patriots’ tendency to do some of the wildest things the sport has ever seen is due to the simplest thing in athletics.

“These guys do not get tired,” veteran wide receiver Kenny Britt said Monday night. “It reminds me of when I was a little kid, I was running around never getting tired, no one other kid was getting tired, or like when I watch my kids now. Just running and running for hours, never stopping for a drink and never getting tired. These guys can run all day.”

The secret here isn’t running; that isn’t so much a secret as much as it is the most common thing in the history of sports. Instead, it’s getting the Patriots to run in specific patterns to condition them in granular ways. It is nearly impossible to simulate four quarters of football, long snapper Joe Cardona said, but the Patriots get close.

“The conditioning is geared toward game performance. It’s not running to run. It’s running for a very specific event — a special teams play, a long offensive drive, a defensive stand,” Cardona said. He lays out this practice drill: After a punt, there’s a dead sprint to cover the kick. This, of course, is a “very taxing” run in the first place, but Belichick is preparing for something even more specific. They practice kicking, a penalty that negates said kick, the walk back to the spot 5 yards behind the original line of scrimmage, then a re-kick and its subsequent dead sprint. “We come back and do it again,” Cardona said. “It is not the easiest thing.” The goal here, he said, is to get players in shape to sprint but also conditioned for this specific in-game scenario.

“The conditioning is geared toward game performance. It’s not running to run. It’s running for a very specific event—a special teams play, a long offensive drive, a defensive stand.” —Patriots long snapper Joe Cardona

Patriots players who’ve also played elsewhere said that many teams take conditioning far less seriously or fail to apply it as specifically as New England does. Every team trains for football scenarios. Everyone focuses on explosion and being able to run short distances, but no one does it with more consistency, rigor, and smarts than the Patriots. It’s a microcosm of the organization’s philosophy as a whole: taking a simple thing and doing it better than anyone. None of the Patriots I spoke with have played for a team with the practice consistency of the Patriots — the same practices in September as December. Martellus Bennett remarked last year, for instance, that he could not believe the Patriots were still running the hill during the playoffs. In his memoir, Julian Edelman referred to it as “the fucking hill.”

“Football has a very unique energy system,” Cabrera said. “Look at hockey. You’ve got shifts that are about 45 seconds. In football the average length of a play is five to seven seconds then 40 seconds to recover. What other sports do that? None of them.” This, he explained, is why the Patriots have put emphasis on tailoring conditioning for exact scenarios. Cabrera said the team is training not just physically but mentally, by honing the ability to push through fatigue in specific game situations. “We are making sure we have enough sustainability to make it through — not just make it through but thrive,” he said.

After the Patriots beat the Jaguars in the AFC championship game, defensive back Devin McCourty credited the team’s conditioning workouts.

“Early in the season, Bill said, ‘We have to get in better shape, we have to do this, so we are running hills,’” McCourty said.

Everyone on the team hates these runs — particularly the three-minute run.

“I hate it. I hate it,” defensive back Brandon King said. So how do you convince your body to do it? “There’s no convincing. It’s our job. Do it or get fired.”

This fast-paced three-minute run, Cardona said, is interval training: “It’s more than a jog, less than a sprint.” Cardona played football at the Naval Academy, which involved a lot of running, but not the kind he’s done in New England. “I had to adjust. The ability to go for a 5-mile jog is not going to help you. You have to develop the ability to run for a few seconds, then do it again for however many plays it takes.”

“I hate it. I hate it,” defensive back Brandon King said. So how do you convince your body to do it? “There’s no convincing. It’s our job. Do it or get fired.”

Defensive lineman Ricky Jean-Francois, who has played for five NFL teams, said he had not spent a great deal of time thinking about conditioning in football before coming to New England. But he’s done plenty of it since joining the Patriots this season. “When the fourth quarter comes and with the type of game we play here, you’ve got to be built for four quarters, literally,” he said. “With the running — when the fourth quarter does come, you’re not tired, you’ve got energy.”

Jean-Francois has even tailored his own conditioning to moments that apply to his position. He said he runs sprints for the maximum distance he’d cover on a play: 30 yards if he chases the ball on a big gain. So he runs the sprints over and over to simulate the snaps of a play. “I’m not going to try to run 6 miles because I’m not going to ever do that in a game.” Now that he’s thinking about conditioning, he’s considering even calculating the precise yardage he runs in a game and making the sprints more exact.

Belichick, of course, loves making his players run, but not because of some drill-sergeant mentality. No, he loves how it helps his team win. Last month, he raved about the offensive line’s conditioning and offered an odd breakdown of how he evaluates the team’s running: “I stand right there when they run and I can feel them run by. I mean, I’m not timing them, but I can feel when they’re running fast. I can feel when they’re not running fast. I can feel when they’re breathing heavy. I can feel when they recover quickly.”

Late in the game, players say that their superior conditioning shows up in every phase of play.

“It’s torture,” Britt said of the running, with a laugh. “It’s something that most athletes would go into not wanting to do — until you see the effects on Sunday, when you see how we run in the fourth quarter and how other teams run in the fourth quarter. It’s totally different.”

“You can definitely tell on the tape — how a tired [opponent] moves, how he comes off the ball, his technique. In the fourth quarter, he gets a little sloppy,” Britt said.

Like Bennett said last year, will New England keep running up until Sunday’s game?

“There are no shortcuts here — we practice the same now as we did Week 1, and it gets embedded in you,” King said. “We’ve been running for so long that you don’t feel like you’re running anymore.”