Thin is in with some of the biggest members of the 49ers.

Just ask guard Marcus Martin, who has lost about 10 pounds after playing around 330 last year and plans to drop several more before the season starts. Martin, who entered high school at 360 pounds and was too heavy to play Pop Warner, has said he’s in the best shape of his life.

The reason for the reduction? The 2014 third-round pick indicated it’s a mandate from head coach Jim Tomsula and offensive line coach Chris Foerster.

“Oh, man, it’s a whole different mentality, a whole different level of fitness,” Martin said. “Coming in coach Tomsula said he was going to be the only fat guy in the room. And that hit home. You had to get in shape and get right.”

Why the added emphasis on fitness for the front five? According to Martin, Foerster’s philosophy is similar to that of Mike Solari, the 49ers offensive line coach from 2010-14. That said, Foerster has used zone blocking extensively in his 16 years as an NFL offensive line coach. The zone scheme requires more movement and athleticism than the power-based approach employed by Solari. In addition, the 49ers could employ a faster-paced offense in 2015: Offseason practices were marked by quick huddles and endless shouts of “tempo” from Tomsula.

Whatever the case, Martin has followed orders as he readies to battle for the starting spot created when Mike Iuapti signed with Cardinals. Martin, who routinely took first-team snaps at right guard in the offseason, figures to face competition from Brandon Thomas and Joe Looney.

“You have a coach (Foerster) that emphasizes being in shape, being able to run and being physical at the same time,” Martin said. “And being able to replicate that every single time. You’ve got to be in shape or you won’t have a job.”

Martin, who turned 21 in November, had a starting job for the final eight games last year after center Daniel Kilgore broke his ankle. It wasn’t an ideal situation: Martin hadn’t played an NFL snap before his first start because of dislocated knee he sustained in the preseason and he finished with the lowest grade on the team (-17.1), according to Pro Football Focus.

Martin believes he’s poised to make a significant jump, partly based on the offseason training he’s done with tight end Vernon Davis, 31, the longest-tenured member of the team.

“I’m much stronger,” Martin said. “There’s a big difference between year one and year two. In year two, you find your place in this league. And I feel like that’s what I’ve been able to do. I’ve been getting a lot stronger and a lot faster.”

Twitter: @Eric_Branch