Early Monday morning, in the sunshine-lit Half Hour Power studio, Wes Welker walked through the door, grabbed a purple training band and went to work. Trainer Howard Waldstreicher stood nearby, providing instructions.

“He calls this a warm-up,” Welker said, raising his eyebrow, and perspiring from the intensity of the core exercises for his back. “Yeah, a warm-up.”

Welker trains relentlessly, this just another long day in an NFL career that critics believe may be running short on remaining time. At age 33, he entered Broncos training camp embracing the scrutiny, delivering a rebuttal with each explosive lateral step and rotational paddle row during his 30-minute, 46-second routine.

“I love it when they say I can’t do it, that I am too old,” Welker said. “It’s something that motivates me, another challenge. From not getting any college offers except from Texas Tech, from going undrafted, from being traded, and from being in Denver now. It’s been one thing after another to overcome. Now it’s being old. Yeah, I love it.”

Finding purpose is easy for the Broncos. Players will participate Sunday in the team’s first public practice at Sports Authority Field at Mile High with a singular focus: Super Bowl victory or bust. Welker recognizes the importance not only of setting an example for younger teammates but of carrying out the team’s message. This can’t be accomplished through poor eating and marginal effort. Looking for an edge, Welker switched to a gluten-free diet three months ago.

“You can’t throw away a day at the gym with a greasy burger,” Welker said of his commitment to more healthy eating.

During the first two practices of training camp at Dove Valley, Welker beat defensive backs with clinical efficiency.

“You have to be about it, not talk about it,” Welker said.

PHOTOS: Denver Broncos training camp, July 26, 2014

After a disappointing end to last season, one interrupted by two concussions, Welker sought improvement. The NFL, he explained between quick-burst drills, demands players evolve or else.

At his wife Anna’s urging — she’s a former model — Welker wandered into Waldstreicher’s Cherry Creek gym six months ago, the sting of the 43-8 loss to the Seahawks still fresh. The workouts, always done from a standing position, focus on lateral quickness, strength and core muscles, shaping the glut to the hamstring to the back.

“If Wes could bench-press 500 pounds, how would that help him on the field?” said Waldstreicher, who has professional tennis players among his clients. “We are doing exercises that will improve his performance, make him fast and injury free.”

The idea of weightless training appealed to Welker for years. He adopted routines at home, but “this workout is what I always wanted,” he said, “and I had never seen it offered.”

Welker recognizes that bulking up will not help him hit the snooze button on Father Time’s clock. In college, he played at 200 pounds and 14 percent body fat, admitting it sabotaged his 40-yard dash and contributed to him going undrafted. He’s faster now than when he left Texas Tech — “He’s lightning in a bottle,” said receiver Emmanuel Sanders — and is 5-foot-9 and weighs 185 pounds, with 4 percent body fat.

“I don’t think it’s bad to lift weights. I just don’t see the need to lift heavy weights,” Welker said. “I have learned that over the years because every time I did, I’d get hurt. I’ve had ACL, rotator cuff, wrist and ankle injuries.”

Beyond football IQ, Welker’s ability to excel hinges on his first step off the line of scrimmage. He makes his money on underneath routes. Those demand precise execution, where one foot can make the difference in a critical third-down catch or an interception. He pushed through lateral drills last Monday, knowing it could cause a cornerback to shade slightly in one direction in his stance, creating a window of separation for Welker.

“That first step is everything. When I have that, my confidence is high. I know that guy across from me is in trouble,” Welker said. “Once he has to cheat to the inside or outside, then it’s like, ‘All day, it’s on. Let’s go.’ “

Part of the 30-minute workout’s appeal was the connection to the Broncos’ offense. The Broncos play at full throttle. Stamina becomes a factor. Welker goes faster, longer in his workouts than required in passing routes to make game speed comfortable.

“Can you get off the ball and get open when you are tired? Can you be strong? If not, you will get mauled,” Welker said. “You want to be sharp when you see that guy across from you with his hands on his knees. I might be hurting, but I want to be ready. If I am able to get that one jab step when he can’t, it makes all the difference in the world. He’s done.”

Watching Welker wring out calories like a kid half his age, it’s hard to imagine his career is near the finish line. His jersey will likely have to be ripped off him.

You’d have to catch him first.

“I love playing,” Welker said. “For me, it’s all about my health. If I feel good, I will keep on playing. There are times where I sit there and think, ‘I can do this five or six more years.’ Then there’s days where I think, ‘This is it!’ I feel really good. Some years, you have to search for motivation. Not now. I’ve got people saying I can’t do it anymore. It’s great. It drives me.”

Troy E. Renck: trenck@denverpost.com or twitter.com/troyrenck

Working out with Wes

At age 33, Wes Welker is old by wide receiver standards. According to footballoutsiders.com, the average snap-weighted age of NFL offensive players in 2013 — those who played snaps — was 27. Welker is attempting to outrun Father Time through his training. His evolution, as described by NFL reporter Troy E. Renck:

In 2003, final college season:

• Welker weighed 200 pounds and had 14 percent body fat.

• Lifted heavy weights, bulked up and lost speed.

• Went undrafted.

In 2014 with the Broncos:

• Welker weighs 185 pounds and has 4 percent body fat.

• Does weightless training.

• Adopted a gluten-free diet.

• Runs faster than he did as a rookie.