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FOXBOROUGH, Mass. — It is almost happy hour on Friday of the 18th week of the NFL season. After practicing earlier in the day, Patriots players are free to enjoy a weekend off. The lot outside Gillette Stadium where they park their cars is nearly empty. Snow is on the ground. A chill is in the air.

Tom Brady could be tickling his adorable kids in his Brookline mansion and listening to their sweet giggles. He could be feeling the warmth of the sun in a poolside cabana somewhere in Mexico, sipping an adult beverage from a poco grande glass with an umbrella in it. He even could be on Justin Bieber's party boat.

Instead, the great Tom Brady is on the practice field in back of Gillette Stadium, passing footballs to Julian Edelman under the watch of throwing coach Tom House.

Brady brought House to Foxborough for a mechanical evaluation and tuneup. House is observing Brady's passing from different angles. Is his arm at 30 degrees or 35 when he throws? Is his aim consistent? Is his foot placement enabling maximum hip drive? Is he effectively balanced?

At 39, Peyton Manning no longer could throw the way he used to. He missed seven starts with a foot injury and had a 67.9 passer rating—easily the worst of his career. And he knew it was time to exit the arena.

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At 39, Brady led the AFC in passer rating, yards per attempt and passing yards per game. The Patriots won 11 of his 12 starts, leading many to believe he was the league's MVP. And he dreamed of playing for another decade.

"It is unbelievable to see a 39-year-old man play like he's 29," says Edelman, his teammate for eight years. "His body hasn't really changed. He may have lost some hair. Other than that, he's still the same."

Brady isn't aging as much as he is evolving, and it is not by happenstance. His objective is not to avoid becoming Manning at 39. It's to become a better Brady.

"I love the game, and I always want to improve," Brady says. "My college coach used to say, 'Better or worse: What's it gonna be?' I love to learn and to see improvement."

The season began for Brady with a four-game suspension resulting from Deflategate. While his teammates were winning three games and losing one, Brady was doing everything he could to make his body feel like he was playing football.

Wearing a helmet and pads, Brady went through the usual quarterback drills. Assistants batted him with padded arms and bags as he threw. Receivers, including former teammate Wes Welker, ran routes for him.

"We trained harder than the sport itself demands," says Alex Guerrero, Brady's body coach. "The four weeks he was off, he worked really hard. He trained so when he came back it didn't look like he had taken four weeks off."

When the suspension ended, it was almost as if it never happened. "Never mentioned the suspension," Patriots receiver Chris Hogan says. "There was no looking back for him, only looking forward."

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Brady's focus was on being a leader, not a martyr. He just started throwing touchdown passes. In his first four games, Brady had a passer rating of 133.9. He credits his quick acclimation to his work with Guerrero.

Brady and Guerrero have been together for a dozen years, since Brady visited him on the recommendation of then-teammate Willie McGinest. In addition to being a team consultant who watches almost every game from the sidelines, Guerrero is a trusted member of Brady's inner circle. He is so involved in Brady's life that he often uses the pronoun "we" when talking about him. He is the godfather of Brady's son Benjamin, as well as Brady's business partner.

Their joint venture is TB12 Sports Therapy Center at Patriot Place, the open-air shopping and entertainment plaza adjacent to Gillette Stadium. With a giant picture of Brady on its exterior, TB12 sits between a spa and a new age workout studio, across from an art gallery.

Brady and about 20 of his teammates regularly take the short drive from the player lot at Gillette up to the private parking area for TB12 and ring the bell to the back door. Mostly they get body work—a form of manual massage—from Guerrero.

In the morning, before practice and after, Guerrero works Brady's right arm and the muscles and tissues around it.

"I think that arm gets rubbed and milked more than the entire cow population in the state of California," Edelman says.

Years ago, Guerrero got into trouble with the Federal Trade Commission for making claims about products that had not been properly tested, but Brady and many of his teammates swear by him. And Brady's performance is a powerful testimonial to Guerrero's methods.

"Tom takes it to heart, and it's definitely working," Edelman says. "He's so pliable and focused on the details of his body."

With guidance from his guru, Brady tries to be better through self-awareness (he meditates), rest and repair (he sleeps in special "athlete recovery sleepwear") and nutrition (he won't eat dairy, caffeine, white sugar or white flour).

For most of the year, Brady is a vegan. In the cold winter months, he adds some lean meat to his diet. A typical day's menu this time of year might include a breakfast smoothie—made with almond milk, a scoop of protein, seeds, nuts and a banana—a midmorning homemade protein bar, sliced up chicken breast on a salad with whole grains and legumes for lunch, a second smoothie as a snack and a dinner of quinoa with greens.

Unlike 49ers quarterback Colin Kaepernick, who had trouble maintaining his weight when he went vegan, Brady has had no problem maintaining lean mass. Guerrero says for the past several years, Brady has weighed 228 at the start of the season and dropped two to three pounds by the end. His body fat holds steady at about 10 percent.

Brady's workout regimen also is nontraditional for a football player. About 90 percent of his training is with resistance bands, and much of it is high-rep. In the offseason, he trains with Guerrero six days a week, sometimes twice a day. During the season, it's three times a day.

"It's unbelievable to see the consistency, how level-minded he stays and how he manages to raise the bar every year," Edelman says. "I don't think I've ever seen anyone like him—no one even close."

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At the beginning of each season, the Patriots run their players through a battery of strength, speed and agility testing similar to combine drills. The purpose is to measure how the players are declining. But the damndest thing is happening with Brady. In each of the past three years, he improved his test scores in every category, according to Guerrero.

"It seems he's actually gotten stronger and faster as he's gotten older," Guerrero says.

Brady laughs it off. "I don't really correlate those numbers to being a better QB, but coaches and scouts like those things."

Brady does allow, though, that "in every way" he feels better at 39 than he did at 29.

"Really in my recovery and how my body feels each week," he says. "I basically always want to feel 100 percent for every practice and game. I know that is not always possible, but that is my goal. For the most part, I achieve that unless I sustain a big injury in the game. Then I have to work hard to be able to be ready for the game on Sunday.

"You can only work as hard as your ability to recover. I am confident in my process, and I feel there is not another 39-year old in the world that can recover faster than me. I have been blessed to learn the right methods, through my nutrition, hydration, pliability and proper rest. It's really not that hard if you do the right thing."

Last offseason, Brady made an honest evaluation of his play, as he does every offseason. Self-honesty has always come easy for him.

He thought he could make better use of downfield passing opportunities. He thought he could make more plays with his feet.

"Those are things that [could] really help our offense," Brady says. "They really help any offense.

"Hopefully we can make some big plays in the postseason, either throwing it deep or by extending plays. It takes pressure off of everybody if we can make two big plays per game. I have tried to improve those areas by focusing on how to improve them [and] working on my mechanics with my deep ball and my training methods for mobility. If you are working on the right things, the right way, I have no doubt I can continue to improve."

Brady ran a 5.28 40-yard dash at the combine 17 years ago. He never is going to be an Olympian in track and field. But he moved well enough this season to make first downs on 35.7 percent of his runs. That was the ninth-best percentage among starting quarterbacks, according to Sporting Charts.

He also has improved at moving in the pocket and extending plays. On a 3rd-and-16 against the Jets in December, Brady was flushed left by Muhammad Wilkerson. He circled backward, reset and found Edelman on a cross route for a 28-yard gain. It was the kind of play no one ever expected from Brady at 29, let alone 39.

It would not have been possible if Brady had not imagined himself a quarterback who could move more like Aaron Rodgers and less like Manning.

"He works on lower body quickness every day, doing band pulls," Edelman says. "He has someone hold the band for him to do his knee drives. He's taken that to heart to try to improve. He sees all these young guys move around with their legs, and he wants to show them he can do it too."

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Brady's throws are supposed to be losing zip, but he averaged 12.2 yards per completion—his highest average in five years and the third highest of his career.

What made Brady's deep passing even more impressive is it didn't come with an offset of more turnovers. Brady's interception percentage of 0.5 was third-best all-time, and the Patriots set a team record for fewest interceptions thrown with two.

Brady's passer rating on throws of 21-plus air yards was 117, according to STATS. That was the best passer rating on such throws of his career.

As he has aged, Brady's sense of measuring risks and rewards has become keener. Maybe more than any quarterback, he understands the importance of not turning the ball over.

Usually, when a quarterback has new receivers to throw to, he becomes more prone to interceptions. But 40 percent of Brady's completions were to Hogan, Martellus Bennett and Malcolm Mitchell—new teammates in 2016.

Brady clearly has mastered the art of connecting quickly with new receivers.

"Tom takes the time to talk to guys," Hogan says. "He makes sure when they are on the field together, they will be on the same page. He's an MVP, one of the best to ever play, and he's still trying to help guys. I've been able to learn a lot from him about playing my position. A lot is being able to read coverages and, in certain instances, how to run a route versus this coverage—not looking at it through my eyes but looking at it through his eyes. Tom makes you understand what he is seeing. He explains he's going to feel good about throwing the ball if, for instance, I go inside a guy as opposed to going outside a guy."

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There is another benefit to self-improvement for Brady. It is a means to improve others. "I enjoy watching my teammates grow and improve themselves personally and professionally," he says. "My motivation may be different than others. I want to be the best I can be for my teammates and coaches every day, and I never want to let them down."

It is one thing to achieve a greatness beyond what has been achieved in the past. It is another to sustain that greatness, and then to not be satisfied with it, and to reshape it and to build on top of it.

It is another thing still to do this as the oldest non-kicker in the league, after winning four Super Bowl rings and three Super Bowl MVP awards, after walking off the field victoriously more times than any quarterback in history, after making more than $196 million in football salary alone and after making one of the most gorgeous women on earth your bride.

This isn't really about arm angles, quinoa and fancy pajamas. It's about a deep, abiding hunger that very few of us could relate to.

When Brady stands in front of the mirror, he doesn't see the GOAT. He sees the quarterback who began his college career at Michigan with six players ahead of him on the depth chart and the one who was forced to platoon with Drew Henson as a senior. He sees the skinny kid who was passed over 198 times in the 2000 draft.

Brady was not born with football's silver spoon in his grasp. He went on a mission to find it. He stole it from Drew Bledsoe. He waged a war over it with Manning, and he refused to let it be taken by Jason Taylor, Bernard Pollard or Rex Ryan.

All of this has served him very well as he has turned his NFL run into an ultramarathon.

"We don't train with the idea he is already the starting quarterback," Guerrero says. "Every year, he's working to be the starting quarterback, and he's got to work hard to do that. He always talks about it. Every year there is going to be somebody there that is going to outwork me if I don't continue to work hard. So in his mind, he has to keep working hard in order to continue to perform at the level he has or to improve."

Jimmy Garoppolo, the team's second-round pick three years ago, is young and hungry and gifted. Many teams would be thrilled to have him as their starter. Certainly, Brady could perceive him as a threat.

In training camp after the team cleared the field, Brady sometimes challenged Garoppolo to play "the bucket game," in which the participants try to land more passes in a bucket from the same distance, usually 30 to 40 yards. And when Brady lost?

"Sometimes he wouldn't talk to me for a while," Garoppolo says with a grin.

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Brady wouldn't be mad at Garoppolo, and eventually he would make that clear. He would be mad at himself.

That seems long ago now. Brady hardly is fading as he prepares for his greatest challenges of the season. After missing the first four games of the year and sitting out three practices the past month, he may be as fresh and focused as ever in January.

And now is the time of year when Brady always seems to rise above us like a hot air balloon.

As he and Guerrero reflect on the Patriots' season, Brady's impressive numbers and his age at TB12, they laugh. "This is something that is not a shock for us," Guerrero says. "It's what we've been planning to, come to fruition."

This postseason is an opportunity for Brady to do something no player has done. He can play in his seventh Super Bowl. And he can do something no quarterback has done—win his fifth.

This postseason also is opportunity for him to do something else, something that may be as just as important to him.

This postseason is an opportunity for Tom Brady to improve.

Dan Pompei covers the NFL for Bleacher Report. Follow him on Twitter: @danpompei.