The 6-foot-6, 333-pound Holmes admitted Tuesday that he's not in "the best of shape" to play a full game.
"I need to get in a little bit better shape," Holmes told ESPN.com. "Day after day, I'm progressively getting better."
Holmes maintained his conditioning issues have nothing to do with being overweight. He believes they are more a product of getting accustomed to playing significant snaps after seeing action in just one game as a rookie.
Through the first three games this season, Holmes had played all 191 snaps.
"Sometimes, I just get a little winded," he said. "I use so much energy at times, I just need the wind. ... I have never played like this before. This is really my first action. You're really seeing how much energy you're actually using out there on the field.
"I know I need to pick it up and get in better shape so I can play hard all four quarters."
Holmes said he has taken a proactive approach by getting on the treadmill daily, when not in meetings or at practice.
"I just have to do different things to help build up my endurance," he said. "Any free time I get, I might even just go for a little jog to build up endurance. The first game [Sept. 8 at New Orleans], I realized I wasn't in the best of shape that I needed to be in."
Holmes, a third-round draft pick in 2012 from Southern Mississippi, began the season as the starting right tackle in place of Mike Johnson, who suffered a season-ending broken leg/dislocated ankle. Holmes was moved to left tackle for Week 3, with starter Sam Baker sidelined by knee and foot injuries. Jeremy Trueblood filled Holmes' spot at right tackle.
Holmes started on the bench Sunday night against the New England Patriots, as Baker returned to the lineup and the coaches opted to stick with Trueblood at right tackle. He found himself back at left tackle after Baker suffered a knee injury in the second quarter. Holmes ended up playing 54 of the 76 snaps and performed admirably, outside of a fourth-quarter sack allowed in the red zone.
Baker's status remains in limbo, meaning Holmes will have to be prepared to start against the New York Jets on Monday night.