He seemed happiest pushing himself through those grueling workouts. Clemens called those weeks before Spring Training "boot camp," and he liked the challenge of it all.
Clemens loved being a teammate, too. Late in his career, he was a great teammate to veteran players and a terrific mentor for kids.
Hours after Clemens finished his own work, he'd be spotted in the Minor League clubhouse instructing young guys on everything from weight training to how best to approach bullpen sessions.
When a young pitcher complained about a sore arm, Clemens quizzed him about what he wore to bed.
"You've got to cover your arm in an air-conditioned room," he told the kid. "That's your career. I always wear a long-sleeve T-shirt."
During his final years with the Astros and Yankees, Clemens became a great ambassador for his sport. When he made Minor League rehab starts, he would hold tutorials with young players.
At one stop, Clemens bought new clubhouse furniture and then stayed an extra day to work individually with the pitchers.
By then, he understood how important his presence was. With the Astros, his acts of kindness will not be forgotten.
During his various milestone moments, Clemens handed out mementos, not just to teammates, but to public-relations staffers and clubhouse attendants.
News of his Saturday start for the independent-league Sugar Land Skeeters has produced a flurry of reaction, much of it negative. Some have asked what else Clemens has to prove. He's 50 years old and hasn't pitched a game in the big leagues in five years.
Some have speculated he wants to pitch another game in the Major Leagues to delay his appearance on Hall of Fame ballots by another five years in the wake of steroids allegations.
I don't believe for a minute that allowing us five more years to consider his legacy is more than a small, side consideration.
Clemens is coming back because he loves pitching. He loves the competition and the attention and all the rest.
I have no doubt he'll try to pitch in the big leagues again, whether it be a September start for the Astros or a spot on the Yankees next season.
Clemens is doing it because he's smart enough to understand that nothing he ever does in his life will be as much fun as standing on a mound trying to get hitters out.
He loved pitching in a World Series game, but he also loved Thursday afternoon games in front of 20,000.
Much has been made of his decreased velocity. To Clemens, that only increases the challenge. He was throwing 90-91 mph during his years with the Astros. He occasionally pulled out a 94-mph heater, but not very often.
But Clemens succeeded on guile and smarts and grit. He would drive his manager with the Astros, Phil Garner, crazy by walking guys and seemingly flirting with disaster.
"Geez," Garner would tell his coaches, "I've gotta go get him. I can't let him embarrass himself."
Garner came to understand there was a method to it all, that Clemens was pitching around guys he wasn't comfortable facing and was determined to not give in to an umpire or a hitter.
Clemens had a game plan and he stuck to it. Even without a great fastball, he still could command games. His split-finger fastball was still one of the most effective pitches in the game.
There was a playoff game in Atlanta when Clemens had nothing. He hated the mound, kept pawing at a hole in front of the rubber and looked completely lost at times. Later, he said that was one of the games he'd cherish most when his career was over. He survived, allowed two earned runs in seven innings and got a victory.
What never changed was his fire. The Astros nicknamed a small room behind the home dugout at Minute Maid "The Rocket Hole." They'd hear Clemens down there between innings, screaming at himself and umpires, psyching himself up for the next inning.
One afternoon in the Astros clubhouse, Lance Berkman said of Clemens, "He doesn't get a pitch that's three inches outside. And then he glares at the umpire for 20 minutes and throws the next pitch a foot outside and gets the strike call."
Players were roaring with laughter at the story. But when it ended, one of them, Jose Vizcaino, approached me.
"If you're using this story, please put in there that I didn't laugh," he said.
I looked puzzled.
"I don't want Roger Clemens to think that I laughed at him," he said.
Very few teammates laughed at Clemens. They admired his talent and tenacity and will to win. To a man, they feel they were blessed to get to know him for a while.
They understood why opponents wanted his autograph before games. As Sean Casey once said, "This is one of the games I'll tell my grandkids about."
Richard Justice is a columnist for MLB.com. Read his blog, Justice4U. This story was not subject to the approval of Major League Baseball or its clubs.