ENGLEWOOD, Colo. –At this point last year, Peyton Manning was focused on getting himself ready to play his first NFL game in more than a year.

Now, Manning is far enough along in his rehab that he can spend more time working on his on-field chemistry and timing with the Broncos receivers. Last offseason, he was just getting back on the field himself.

After resting his arm for a few months after the season ended, Manning threw to Eric Decker, Demaryius Thomas and Wes Welker at Duke University last week.

"I'm not sure, you kind of have comparisons to last year and then comparisons to before the surgery," Manning said about how his arm is feeling. "I'm not sure if I'll ever get back – I hope I'll get back to where I was before the surgery, but whether that's possible or not, I'm probably never going to know the answer to that until I stop playing. I'm never going to stop trying to get back to that point."

Whether his arm strength is all the way back to the level it was before the injury or not, Manning's passes had plenty of zip on them for Thomas at last week's workouts.

"I think he's gotten a little stronger, but I can't really say, because it's my first time playing with a quarterback like Peyton," Thomas said. "It was fun this past year, because I'd never had balls come at me like that. I can't say much about the strength of his arm, because I never really played with him the years before he got hurt. I think it's the same."

Manning has talked about the importance of building chemistry with his wide receiving corps, and Monday's start of the team's voluntary offseason program allowed the full group to reunite.

With a year of experience in Denver under his belt, Manning hopes that his increased comfort level will help the team in 2013.

"I certainly hope that I feel more comfortable," Manning said. "And hopefully that'll make a difference and help me be a better player and help our team be better."

Manning said he thinks it could take "three or four years" for his timing to fully develop with Thomas and Decker and said that he expects to be out of the league by the time those two hit their prime.

Through the throwing sessions at Duke and the team's offseason program, Manning hopes to develop that chemistry the best that he can.

"I think it's a process for a quarterback and receiver to really get their timing down the way you want it to," Manning said. "Experience is your best teacher in all three of those phases and you just can't have enough of them. Both of those guys have excellent work ethics, which I appreciate."

Manning credited their work ethics for helping speed the process along. Last year, both Decker and Thomas recorded their first career 1,000-yard seasons.

Manning expects that through the extra offseason of work, those numbers could increase in 2013.

"I really felt like we got the most out of the time we got together last year as we could," he said. "But, we're hoping that we can be better this year. I know those guys are excited to be better players this year than they were last year."

With last season in the rear-view mirror, Manning took time to reflect on his first season back on the field after being unable to play in 2011.

"I certainly had it in perspective that being out of football for the 2011 season and not really knowing what the future held, and whether I was going to be able to play again," Manning said. "I certainly had a great appreciation for 2012 and being back out on the field playing with my new teammates. It was a new atmosphere for me, totally different culture and a huge transition, but I did not take it for granted one single moment, being out there on the field."