The physical sessions were the first for the 23-year-old left wing since he suffered a concussion in a preseason game a year ago, one that cost him the entire 2010-11 season.
"I took a couple hits and I gave some hits, and I didn't really feel anything," Mueller said later. "I'm extremely happy with today. It's another step in recovering."
A healthy Mueller could do wonders for the Avalanche, which lost a franchise-record 474 man games to injuries last year and missed the Stanley Cup Playoffs with a 30-44-8 record and 68 points, the second-worst figure in the NHL.
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Acquired from Phoenix along with Kevin Porter on March 3, 2010 in exchange for Wojtek Wolski, Mueller collected 9 goals and 11 assists in only 15 games with the Avalanche, showing the promise that prompted the Coyotes to select him with the No. 8 pick in the 2006 Entry Draft.
But Mueller suffered a concussion on a big hit from then-San Jose defenseman Rob Blake in an April 4 game, forcing him to miss the final four regular-season games and all six playoff games in a first-round loss to the Sharks.
Five months later, in a Sept. 22 preseason game against Los Angeles, Mueller was whacked in the head with an errant stick and suffered yet another concussion. He missed the entire season and began to wonder if he'd ever feel normal again.
"It's tough," Mueller said. "(Playing hockey) is something you love to do, and then you can't do it for 18 months. It definitely wears on you. But this organization and my teammates stuck by me. There were always smiles and open arms. It was awesome."
Mueller eventually met with Dr. Robert Cantu, a Boston University professor of neurosurgery to learn more about brain-related injuries. It was quite an education, and Mueller has since been fitted with an Easton-manufactured helmet that exceeds the League's minimum safety standards. He's also wearing a tinted visor to shade bright arena lights that could be harmful for previous concussion victims.
"It helps with the glare from the lights up top," Mueller said. "It's like wearing sunglasses."
Once he received medical clearance to work out, Mueller spent a good chunk of the summer strengthening his upper body.
"Last year I was kind of weak and I couldn't protect myself a lot," said Mueller, one of the bigger Avalanche forwards at 6-feet-2 and 204 pounds. "I worked a lot on my neck muscles, tried to get bigger in my neck and support through my head. With the support through the neck and also through your skull and your brain, it hopefully helps and you're less vulnerable out there."
"I'd be lying if I said I wasn't thinking about it," said Mueller, who skated on a line with center Matt Duchene and right wing Milan Hejduk. "I have bigger shoulder pads and I have a great helmet. Things just feel better right now. I don't know if it's (the weight) I put on or the equipment that's helped me to get out there, but I feel a lot better.
"It's still coming. It took a while to get going, but the more you went out there and skated, the more it started coming back. The more you touched the puck, the better. The first game was a little tough, but the second game we got some puck control and we got good plays on net. It was a good day."
Avalanche coach Joe Sacco thought so, too.
"Obviously missing the season last year, the big question mark coming into this year is, how is he going to feel?" Sacco said. "With Peter, we're looking to see improvement each day. His conditioning, that will take a little bit of time, getting used to the game, getting used to the speed of the game again. I thought he was fine out there."
"He's a right-handed shot and when we had him for the short period of time before he was injured, he was very deadly there," Sacco said. "He was a big part of the power play. I'm hoping we can work four other guys around with Peter and have a very productive power play. Not only on the power play but five-on-five too, but that's a special area for him because of his ability to shoot the puck and get it off quick."
Training camps can be pure drudgery for players, especially veterans; but Mueller is actually enjoying this one after being forced to the sidelines for so long.
"To be honest, I kind of feel like a rookie right now," he said. "I haven't been in a game in a long time, and there's something I need to prove. There's no question about that. I definitely need to prove myself. I want to help make this team a championship caliber team where it was.
"Getting up in the morning now … this is hockey season. I'm ready to go and I'm just excited about it."