The word you keep hearing about Byron Mullens is “fresh.”

Fresh, primarily as in rested from six weeks off with an ankle sprain. But also fresh as in reinvented.

This is a guy who showed up in Charlotte last season as the world’s tallest shooting guard. Then Monday night, with a career-high 18 rebounds, he looked like something else entirely in a victory over the Boston Celtics.

“He put his nose in there a lot,” coach Mike Dunlap said of Mullens’ rebounding. “He’s been accused of not being a blood-and-guts kind of guy.”

With good cause; over his first three NBA seasons, 7-footer Mullens averaged just four rebounds a game. If the ball didn’t fall into his hands, somebody else probably got it.

Compare that to the five games he’s played since returning from the ankle sprain: He grabbed 49 rebounds, nearly 10 per game. Twelve of those came against the Los Angeles Lakers and center Dwight Howard. The 18 Monday night were primarily against Boston’s Kevin Garnett.

“I told everybody I’d be so much faster because of fresh legs,” Mullens described Tuesday.

Mullens wouldn’t recommend a sprain that swelled his left ankle to softball size. But he and Dunlap both say Mullens used his time off well. He worked hard with strength-and-conditioning coach Matt Friia and spent hours breaking down video with the assistant coaches.

How do you get in better shape with a bad ankle?

“I got in the pool a lot and ran,” Mullens said. “And a lot of quick-lifting – light weights but heavy reps. Speed stuff to get the heart rate up. A lot of mountain climbs.”

Dunlap planned to use Mullens no more than 14 minutes in his first game back, on the road against the Miami Heat. Mullens was in such good shape, and in such quick rhythm, that he played 28 minutes, finishing with 12 points and nine rebounds.

The Dunlap-Mullens relationship is intriguing; Dunlap joked earlier this season that Mullens responds well to “threats.” There’s truth embedded in that humor.

“I’m able to tell him things he doesn’t like to hear. There’s a trust there,” Dunlap said.

An example Dunlap cited after the Celtics game: “You’ll get your touches, but you’ve got to get your back to the basket.”

Mullens tends to default to long jump shots. He hit four of five 3-pointers Monday. Dunlap demands that Mullens post up more, in part because it broadens his skills, in part because he’s the best offensive big man the Bobcats have.

Tuesday, after most players left practice, Dunlap took Mullens to a basket and spent 30 minutes drilling him on post moves, forcing Mullens to dribble in traffic against smaller men.

How’s that coming?

“It’s getting better. I’m learning to deal with strong guys like (Metta) World Peace or Garnett,” Mullens said. “It’s getting low and staying patient …”

And staying fresh.