In the offseason, Brantly didn't spend too much time resting. Instead, he used the four months to take his conditioning to new levels.
The San Diego native is a big believer in CrossFit training.
The rigors of catching certainly are demanding, but so is running 1 1/2 miles up a steep incline to the top of a mountain, which he did on numerous occasions.
To Brantly, athletes in all sports can benefit from CrossFit training.
"CrossFit is a great avenue for any athlete," said Brantly, whose trainer is an ex-Marine named Brian Nelson. "I used it quite a bit in the off seasons."
How does CrossFit relate to preparing for baseball?
"It's all transferrable," he said. "You're working stability. As a catcher, the game can be like climbing a mountain sometimes. When a game drags a little bit defensively, you have to stay on your toes every single pitch throughout an entire game. And you have to keep your mind on what you are doing."
The Marlins will be demanding a great deal from Brantly, who is entering his first full season with the organization.
Miami acquired the left-handed hitting catcher from the Tigers last July as part of the Omar Infante/Anibal Sanchez trade.
Late in the season, he became the regular over John Buck.
Brantly showed promise at the plate. In 100 at-bats, he hit .290 with a .372 on-base percentage.
The Marlins' catching position took a blow on Saturday when backup Jeff Mathis fractured his right collarbone on a foul tip. He will be out about six weeks.
"It's extremely unfortunate," Brantly said. "You don't want to see that happen to anybody on either side of the field. It's upsetting to me because he's been helping me out a lot.
"He told me, when he's around he will answer any questions I might have. And to call him any time when I have questions. He will still help the team, even though he will be off the field for now."
In terms of conditioning, Brantly has certainly taken the necessary steps to handling a heavy work load. A number of those steps came involved running up mountains.
A few months ago, Brantly traveled to Scottsdale, Ariz., to watch some Arizona Fall League games. As part of his trip, he sprinted up Camelback Mountain in Phoenix.
"It's like a mile-and-a-half to the top," he said. "If you go up the steep side, it's kind of like a test of will. Little stuff like that, it helps you with cardiovascular, but it's kind of a mental test too."
Brantly's running and CrossFit regimen started a week after the 2012 season ended. He took a few days to recover, and then started hitting the weights heavy.
He kept up his intense routine all the way up to Spring Training.
In California, he would run Runyon Canyon in Los Angeles. And he ran a mountain in San Diego.
"Then I will go to the beach and run in the sand," he said. "Extra stuff like that, it kind of mixes up your workout."
Typically, Brantly would run three or four times a week. His strength training was three days on, one day off.
"It helps build my mental strength," he said.
Since the start of Spring Training, Brantly has been on the move, catching numerous bullpen sessions with as many pitchers as possible. Miami has 38 pitchers in camp, and Brantly is familiarizing himself with as many as possible.
"We're here, working hard and getting to know each other as a team," he said. "I try to find individual time to talk to each of the pitchers and try to get to know them on a personal level, too. I'm trying to know the personalities they have."
Handling the staff is a top priority, but like CrossFit training, Brantly has a passion for hitting.
On a youthful team, the Marlins will be looking to scratch out enough offense to stay competitive. Brantly has always been productive at the plate.
"I love hitting," he said. "I can't wait to do it. I trust my hitting process. I believe in myself as a hitter, as a player and as a catcher. Just go out there and trust my abilities and know what my abilities are and not try to do too much. I do what I'm capable of, and just play it from there."