But those physical changes may not have had nearly the impact they did if he didn't also overhaul his mental approach. That, along with his sense of humor, will help him more than anything in facing his latest challenge.
After struggling to find consistency following his big league debut in 2005, McCarthy began to make mechanical changes in '09. The results included more groundballs and finally success on the mound in '11.
"I tried to change everything I could as much as I could possibly overhaul and just become something different," said McCarthy, who signed a two-year, $15.5 million deal with the D-backs in December.
After making the mechanical adjustments and harnessing the movement on his two-seamer, McCarthy needed one last piece to make the transformation complete. Then he discovered the "The Mental ABCs of Pitching," written by the late Harvey Dorfman.
It's one more similarity he has with Halladay, who credited the book with helping save his career after he was demoted to Class A in 2001 with the Blue Jays.
"A lot of it was tied in mentally," McCarthy said of his transformation. "I didn't feel confident in myself as it was and I knew I needed to make some changes. I really started digging in that book and could see the value there. The first few times I pitched after reading that, it was just like a weight comes off you and you feel relaxed and like, 'OK, this is how it should be, it's way more simple.' You come out of the game and you don't feel like you're dead and drained emotionally. You've been where you needed to be and you've simplified it."
The basic premise of the book is to focus on one pitch at a time, letting go of everything that happened before that pitch and everything that could happen in the future. Complete focus should be on the task at hand.
Talk to a pitcher after a bad outing and a lot of times you'll hear that an inning just got away from them, that things began to spin out of control after a bad pitch or a mistake made behind them. Concentrating completely for 100-plus pitches requires a mental focus that takes discipline and practice.
"It happens really quick," McCarthy said. "Even when you're really locked in, a thought pops in there that you don't want in there, and you're thinking about what to think about. And the next thing you know, you're out of the game and what looked like would be a great game isn't. And you realize how fast that goes, and if you're not extremely vigilant, it just takes over. It's like our brains are just trying to take us somewhere else where we're not supposed to be. You have to fight it and teach it what you want."
So McCarthy began to train himself to completely focus on the task at hand. He found it applied not just on the mound, but to the work he did to get ready between starts.
If it was his day to work in the weight room, he focused completely on that. Studying video of hitters? Be locked in on it. Focus on the process and trust the end result will take care of itself.
"He's very into preparing for a particular team," said Bob Melvin, his manager in Oakland. "When he takes the mound, he's very prepared and therefore he's very confident in his game plan, and I think that's just as much a part of his transformation as slowing the game down."
McCarthy will use that focus to not let himself be consumed with coming back from a life-threatening injury he suffered last year.
Struck in the head by a line drive off the bat of Erick Aybar on Sept. 5, he suffered a skull fracture and brain contusion and was unable to pitch again the rest of the season.
While the injury was horrific, McCarthy used his sense of humor and focus to deal with it.
"The not being dead part is good," he joked. "But I'm not someone who every day is counting blessings or thinking about it. I think it places too much weight on what happened. There are people in a lot worse situations and in a lot more danger, and if they can somehow get through it and do it, then obviously you can convince your brain to do it. If it were something that I could actually make an adjustment to, or do something differently on my end, that would be one thing, but that's not the case. I feel fortunate that I still have a chance to go out and play, but beyond that, that's as far as I try to think about it."
Teammate Trevor Cahill, who played with McCarthy in Oakland, says McCarthy's focus on statistics is helpful for this situation.
"He's a big numbers guy and he knows that the odds are that it won't happen again," Cahill said.
McCarthy was cleared by neurologists early in the offseason, so he expects there to be no lingering effects from the injury. His main concern, and that of the D-backs as well, is his shoulder.
"I've had, in four or five of the past six years, a scapula stress fracture, which doesn't happen," McCarthy said. "I've got almost all of them in baseball history. It's just become my injury."
The D-backs are hopeful that their medical staff, which they consider to be ahead of the curve in injury prevention, will be able to find a way to keep McCarthy healthy for a full season.
Like with everything else, McCarthy figures if he can stay healthy, the rest will take care of itself.