SANTA CLARA, Calif. -- From the moment the San Francisco 49ers used the No. 2 overall pick in the 2019 draft on Nick Bosa, coach Kyle Shanahan has never doubted what he was going to get from his star defensive end.

Asked recently if he's ever coached a rookie who didn't play or act like a rookie, Shanahan playfully took it a step further.

“Bosa," Shanahan said without hesitation. "Bosa has been a professional since he was three years old.”

After transforming the Niners' defense into one of the league's best as a rookie, Bosa suffered a torn ACL in his left knee in Week 2 of 2020. In 2021, Bosa bounced back with the best season of his young career, racking up 15.5 sacks en route to his second Pro Bowl.

Three years into his NFL career, Bosa isn't satisfied with what he's accomplished. The loss to the Kansas City Chiefs in Super Bowl LIV doesn't sting quite as much as it once did, but Bosa says it made him realize he hates losing more than he likes winning. To a lesser degree, Bosa was at least mildly annoyed he didn't so much as receive a vote for NFL Comeback Player of the Year last season.

Consider it additional motivation for Bosa, who was able to spend his offseason training with his brother, Los Angeles Chargers edge rusher Joey Bosa, in Florida instead of rehabbing from a knee injury and looks poised to take his game to another level.

"It's been completely different," Bosa said. "Last year, I didn't really take any reps until a couple of weeks before the year. Just being able to get out there and have my body adapt to playing football has been the most enjoyable camp that I've been a part of."

If Bosa can stay healthy, it's not outrageous to think he could earn the NFL Defensive Player of the Year Award and a lucrative contract extension that makes him the league's highest-paid defender. Which is why the Niners are doing all they can to protect him in this preseason, giving him the occasional day off and making it clear he won't play in any preseason games.

"He's one of the best I've ever seen," defensive coordinator DeMeco Ryans said. "Just the way he works and the way he shows up and makes plays, he makes it look easy. And I know it's not easy ... One of the best D-ends in this league. And again, I'm happy for him because he's coming in this year, he's not worried about rehabbing an injury. Nothing to worry about but getting better as a football player, so it's exciting to see where he's going to go."

That Bosa was able to spend the past six months training with his brother and not enduring a tedious rehab is no small thing considering the extent of the Bosa brothers' offseason regiments. Four days per week (every weekday except Wednesday), the Bosas trained near their homes in Fort Lauderdale. It included a 7 a.m. run, breakfast and a trip to the gym that Joey built. They'd lift there until about 1 p.m., followed by a stop in the ice tub before going home to relax. Two of those days were focused on speed training and lateral movements with upper-body lifts and two others were geared toward agility drills and lower-body workouts.

Mixed in is plenty of flexibility and mobility work intended to reinforce the type of movements they do on the field. The idea, according to Nick Bosa, is to "build up our bodies for a long season." Specific pass-rush training is also incorporated as the offseason goes on. For meals, Bosa has a personal chef who prepared him a diet consisting exclusively of vegetables, fruit and meat with no bread or pasta.

When it comes to Bosa, forget the "best shape of his life" cliché. It might be that the only person who will report to any camp in better shape than Bosa in 2022 is Bosa in 2023.

"He looks like somebody literally etched him," left tackle Trent Williams said. "He's like a sculpture. You don't get that way by just waking up, eating cereal and playing the game ... It's no secret to why he is good as he is. I mean, it's obviously the talent is there, but the work ethic obviously enhances the talent."

As a rookie, Bosa was second in the NFL in pressures (60) but managed just 9 sacks. He was able to convert more last season, finishing with 53 pressures (tied for fifth) and 15.5 sacks (fourth). Since Bosa arrived in 2019, the Niners' pressure rate is more than 6 percentage points higher with him on the field than when he's not, and over the past five seasons, only Los Angeles Rams defensive tackle Aaron Donald averages more pressures per game than Bosa's 3.3.

That production has come despite an increase in the amount of double-teams Bosa faces.

In 2021, Bosa faced a double-team on 25.9% of his 313 pass rush attempts, the second highest percentage in the league. As the season went on, Bosa began to find ways to make an impact even when doubled and created opportunities for his teammates to make plays, as the Niners posted 13.5 sacks on plays when Bosa had the initial pressure, fifth most in the league.

As plenty of contract drama unfurled around him this offseason, Bosa never once expressed concern about when his payday might come. That's because Bosa and the Niners have been in no rush to get something done. San Francisco likes to wait until a player has one year left on his deal before negotiating (the Niners exercised Bosa's fifth-year option for 2023 in April). And if Bosa has the big year everyone expects, he'll have maximum leverage for negotiations that are expected to coincide with a significant salary cap increase.

"What I do know, as long as we're here, Nick Bosa is going to be a part of the Niners and he's going to get paid handsomely to do so," general manager John Lynch said. "His time is coming, and when it does, he’ll get what he deserves because man, what a special player."