The 6-foot-4 Mariota, who is officially listed at 222 pounds, admitted he is "a little bit heavier" and added between 5-10 pounds, before providing a reason on why he packed on the extra weight.
"When it comes down to it, just being able to absorb the hits, being able to be healthy for a full year," Mariota told reporters, via the Titans' official website. "Those things haven't really happened yet, so I'm doing my best to be able to be on the front end of it and allow myself the opportunity to play all 16 [games]."
Since entering the league in 2015, Mariota hasn't played a full schedule, missing eight games over that span to a variety of ailments.
Mariota, who spent time in Hawaii in recent months getting healthy, explained his offseason regimen to put on the extra pounds included a combination of diet and weight training. His overall goal surrounded obtaining "good weight, not bad weight" so as not to limit his skill set as a mobile quarterback.
"I think that's why we're trying to find a happy medium," Mariota said. "There isn't a specific number. It's really coming down to when I get out here, do I feel like I can move? Do I feel good with the weight? And if that is, just kind of continue to see how heavy I can get where I feel good and the happy medium is met."
Mariota's weight gain was met with approval by head coach Mike Vrabel, who told reporters what he was hoping to get out of the quarterback.
"Looking for a strong player; this is a big league," Vrabel told reporters. "I can remember playing against John Elway and Dan Marino, and these quarterbacks that -- they're big men. We play against Deshaun [Watson], he's a big player, and Andrew Luck, so I just want to make sure that we're doing everything we can and he's doing everything he can to stay healthy and stay durable, and to be able to help us on the field."
Meanwhile, the upcoming regular season will be important for Mariota, who enters the final year of his contract.
Mariota is scheduled to earn a base salary of $20.9 million, but could set himself up for a lucrative payday if he proves he can play a full 16-game schedule in 2019.