For young players, Danny Trevathan said, a day off is just that. They go home, lounge on the couch and wonder why they’re stiff the next day.

At 29, Trevathan is not a young player.

“Now an off day means off to my own time, taking care of myself,” he said.

The Bears inside linebacker stretches, does yoga, works out, plays with his kids and cooks. It’s all part of preserving his body as he gets older — especially the cooking.

Trevathan changed his diet in the offseason, ditching bread and combining elements of offseason eating that had worked for him in the past. He doesn’t eat anything with more than two legs.

“It’s all about being strict on it and being sound with it,” he said. “It’s like practicing every day to be better at football.”

He focused on explosive workouts this offseason. He ate chicken, turkey and fish for dinner. His favorite dish to cook is chicken curry — heavy on the spice — though he backs down on the fire during the season. He grills chicken and makes turkey with rice. Then there’s the fish. He eats salmon, trout, grouper, snapper and walleye. He started eating halibut at his grandma’s suggestion.

The result: He’s down from around 13 percent body fat to 8 percent.

“Health is wealth,” he said.

That has never been more true than this season. Entering the last year of a four-year, $28 million contract, Trevathan will be a free agent in March. He’ll turn 30 the same month — a scary number in the NFL, particularly when you play on a team that will give out contracts to its young, dynamic players in the next year.

“People look at sacrifice as a bad thing,” Trevathan said. “It’s a great thing — because it’s about your future. Sacrifice now to reap the benefits later. When you sacrifice stuff, you do with a full heart.”

It’s not easy. It has been forever since he has had a steak.

“Anything worth it is going to be hard,” he said. “You have to be professional. You have to know when to say no about that stuff. But I don’t play — not when I’m talking about my body.”

Trevathan — who played all 16 games last year for the first time since 2013 — feels faster.

“They haven’t seen me open it up yet,” he said. “But I have some wheels.”

Inside linebackers coach Mark DeLeone said he has seen Trevathan take care of his body every single day. Coach Matt Nagy has noticed the linebacker’s quickness when he covers running backs in practice.

“These guys, as they get older, their knees start getting beat up — sometimes you can get overweight,” Nagy said. “He’s done the exact opposite. He’s flashing on tape, and that’s a great thing.”

A Super Bowl champion, Trevathan knows how precious a promising team can be. After winning only a quarter of his games in his first two years with the Bears, Trevathan relishes the potential of a team that went 12-4 last year.

“It’s the most important year,” he said, “because it’s all we have.“

It’s another chance, too, to make a statement about his own career.

“I want to be the best person I can be,” he said. “I want to be the best linebacker in the league. I want to leave no doubts in people’s minds.

“I’ve been doing it for a while and I’m still one of the best at it. And I want to be the best when I retire or when I’m done playing football. I want to put a staple in it and have some fun this year and stay healthy the whole time, fly around and make some plays in this defense.”