Heyward-Bey checked the time and shook his head.
''It was almost 10 o'clock,'' Heyward-Bey said with a laugh. ''I said, `You go ahead. I'm going to go home and sleep.'''
So away Brown disappeared for another solitary workout. Nearly five months into another season packed with GIF-generating touchdown celebrations and looks-like-a-typo numbers, the Pittsburgh Steelers wide receiver is still pushing, driven by a relentlessness that is nearing mythical status inside his own locker room.
''He's the hardest-working dude in football,'' Heyward-Bey said.
It sounds like a cliche, particularly in a league filled with overachievers. Yet the Steelers insist it's true. How else to explain how a sixth-round draft pick - one who at 5-foot-10 and 180 pounds hardly fits the prototypical mold of a gamebreaker in a league where bigger is almost nearly always better - becomes arguably league's most fluid player? Heading into Sunday's game at Baltimore, Brown is first in the NFL in yards receiving (1,586), second in receptions (116) and perhaps unmatched in sheer tenacity.
''(He) was kind of bound and determined to not just be the small guy who wasn't your typical wide receiver,'' quarterback Ben Roethlisberger said. ''I think that always pushed him, small school, multiple colleges, maybe people not always believing in him, just fueled his fire.''
One that is singeing opponents at a historic rate. Brown and Wes Welker are the only players with three consecutive seasons of 110 or more receptions. When Brown lit up Denver's No Fly Zone for 16 catches last week, he became the first receiver to put up two games of at least 15 grabs in the same year. His 4,783 yards (and counting) since the start of 2013 is the third-most productive three-year stretch ever, trailing only Jerry Rice and Calvin Johnson.
While it's easy to get caught up in Brown's showmanship - do a quick search for ''Antonio Brown celebration'' for a refresher on everything from the front flip into the end zone against Oakland in November to the goalpost splat against Indianapolis three weeks ago - it obscures the larger point: all that glitz comes with a heavy dash of grit.
Not that Brown wants to talk about it. If anything, he's become more selective with his words as his star has risen. He began his career sharing a corner of the locker room with fellow receivers Mike Wallace and Emmanuel Sanders (the self-described ''Young Money Family) only to migrate to one adjoining the equipment room, better for a quick escape on the days he doesn't feel like chatting. When pressed on the details of his training regimen, Brown offers only vague generalities.
He prefers not to talk about his rise from draft afterthought to perennial Pro Bowler, repeatedly stressing he is ''singularly focused'' on beating whatever team the Steelers happen to face that week and flashing a smile that indicates prying any further is pointless. It's as if he's protecting some sort of secret formula, even from the guys he lines up alongside.
''He's all about his business,'' Heyward-Bey said. ''It's like he turns on a switch. It's time to play ball.''
An ethos that isn't relegated to Sundays. Brown long ago started wearing his game pants during organized team activities. During training camp, he started running additional sprints with the defense even after the offense's five-minutes of oxygen-sapping dashes were done. Soon, running back Le'Veon Bell and the rest of the skill players were joining in. Brown treats every snap of every practice like it's overtime in the Super Bowl whether the ball is coming to him or not, an example that has trickled down through a group that includes Heyward-Bey, rising star Martavis Bryant and protege Markus Wheaton.
Brown's urgency combined with the ingenuity of offensive coordinator Todd Haley and the open-mindedness of head coach Mike Tomlin have created a system that has made Brown nearly unguardable. The Broncos came to Heinz Field last week with the NFL's best pass defense and Brown finished with 189 yards and two touchdowns, including the game-winner between two defenders late in the fourth quarter. Most of the production came after Haley started experimenting and lining Brown up in unfamiliar places to give the Broncos a different look.
''It was like an unscripted training camp scrimmage, if you will, in that second half, all of it in order to get him in some (favorable) spot,'' Haley said.
In other systems with other franchises, that might have never happened.
He fits the physical profile of a slot receiver, but matches it with the football IQ of a quarterback and a chip on his shoulder roughly the size of the Lombardi Trophy. Haley can't even remember if he gave Brown much consideration when Brown came out of Central Michigan in 2010 and Haley was coaching in Kansas City. When Haley arrived in Pittsburgh in early 2012 to take over as offensive coordinator, he wasn't exactly sure what he had on his hands.
''I'm looking at this 5-10 guy. Yeah, he's fast, (but) he didn't fit that prototypical big-dog receiver,'' Haley said. ''I learned pretty quickly not to place a ceiling on AB because he's going to shatter it.''
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