ENGLEWOOD, Colo. -- The last time most of the NFL saw Denver Broncos quarterback Peyton Manning play, he was unrecognizable.

Manning looked frustrated, flustered, impatient, injured and every bit his 38 years in the Broncos' 24-13 loss to the Indianapolis Colts in the divisional round of the playoffs. His body language was loud and clear: Manning was out of sorts and couldn't rebound.

That game remains the last impression many have of him. It was also his starting point in a methodical, straight-talk-filled decision to return for 2015.

Peyton Manning ended the 2014 season in frustration, losing to the Colts in the divisional round of the playoffs. AP Photo/ Eric Bakke

As Manning wrapped up his offseason work last month, with training camp on the horizon, he broke down why he decided to return for his 18th NFL season. In the end it came down to mind, body and spirit.

The first step, of course, was finding out whether the Broncos -- who had parted ways with coach John Fox and several assistants after that early playoff departure in January -- wanted him back.

"There were two times in my career when I didn't really know what was going to happen, it was four years ago with the [neck] injury with the Colts and then this past offseason, kind of what direction are they heading in here and am I a part of it?" Manning said. "There was a bit of that unknown. ... I think people like to know what's going on, what direction they're going, where I fit in, do I fit in? What's the plan?

"It's probably more common to have unknown than to always have the known, and I've had the known 16 out of 18 years [in the NFL], so that's, kind of going back to my injury, I never really said: 'How come this injury happened to me?' Because injuries happen to everybody, they just hadn't happened to me until that point. ... So, all of that is kind where you are as you make a decision."

The Broncos hired Gary Kubiak as coach in January. He hired Rick Dennison as offensive coordinator. Kubiak plans to build an offense that runs the ball and protects Manning better -- one that forces defenses "to defend the whole field." He made it clear he wanted Manning back, but also wanted the quarterback to be at peace with whatever decision he made.

"I guess I looked at what he did last year and just thought, he's coming back because he was still at the top," said Broncos wide receiver Emmanuel Sanders, referring to Manning's 4,727 passing yards, 66 percent completion rate and 39 touchdowns in 2014. "We didn't get the end of the season we wanted, everybody was disappointed; I don't think anybody can think about later right then."

Chasing history Peyton Manning is second on the career passing yards list, just 2,147 yards behind Brett Favre. Since joining the Broncos, Manning is averaging 309.7 passing yards per game. At that pace, he would break Favre's record after seven games. Player Yards Brett Favre 71,838 Peyton Manning 69,691* Dan Marino 61,361 * 309.7 passing YPG from 2012 to 2014

Manning said he is less on edge with a plan in place. After hearing the team wanted him to return, the next step was a no-B.S. physical. Manning needed assessment of his recovery from the thigh injury he suffered in December, his arm strength and his ability to move in the pocket. So in early February, Manning went home to New Orleans to visit with trainer Mackie Shilstone.

"I think you like to know in February, kind of where you're going to be, in March, in April, kind of what's going on," Manning said. "Stress is a word you always try to avoid. It's not healthy for you; but I guess my nature would be I really like to know what's going on so I can get to work on it. What do I need to do? Let's get going, otherwise you're behind."

Shilstone, who has worked with a variety of high-profile athletes, including Serena Williams and baseball Hall of Famer Ozzie Smith, was charged with answering Manning's questions. The future Hall of Fame quarterback said he was willing to walk away if he got "the tough answers."

"I did that personal assessment, I worked with a trainer to really get that answer, to say, 'Hey, let's ask the hard questions, let's find out, is there something I'm not seeing here?'" Manning said.

Shilstone went through Manning's laundry list of questions and gave him the green light physically to play another season.

Now that Manning was assured the Broncos wanted him back and physically he could still play at a high level, he had one last hurdle to clear.

Peyton Manning is currently second on the career passing yards list, just 2,147 yards behind Brett Favre. AP Photo/David Zalubowski

"After you kind of get that physical answer you look at what it takes to prepare for a season and to play in a season," Manning said. "Of course, then you ask yourself, do you like doing that work in February? If I thought this was a drag, there's a couple ways you could go, a couple questions you have to answer.

"I always felt like I knew what I wanted to do, I just wanted to make sure physically and mentally, things were checking out like the way you wanted them to do. To me they all have to match up. You can't feel good physically, but boy, I dread going to do this; that's not being fair to the team. I thought it was a good, a really good, physical and mental assessment. I got honest answers."

Honest enough, Manning said, that he believed he could fit into the Broncos' offense, "do my part for this team" and find a comfort zone he did not have in that January loss. Once he agreed to a $4 million pay cut -- money he can earn back if the Broncos win the Super Bowl -- Manning had all of the boxes checked.

"I wanted to be here, this is where I wanted to be," Manning said. "So, don't look back. I was glad to get that part of it resolved and let's go. To me, it's all kind of supposed to answer itself. I don't think I've been shorted as far as playing. Even like a few years ago, if that had turned out differently, 13 years of unbelievable health and playing, that's special."