Pitcher Hiroki Kuroda, who is now completing his sixth big league season following 11 years in Japan, said recently that his future after this season is up in the air — just as it has been since 2012.

“For me, each and every year has to be its own challenge,” said the 39-year-old Kuroda, who is completing his third, one-year deal with the Yankees. “I want to go through the year pitching every game so that I have no regrets. And should I feel I’ve reached my limit, then that is the easiest way to go out. I think that will make it a decision (to quit) for me.”

In an exclusive interview at Yankee Stadium in New York, Kuroda said he would not rule out a return to pitch in Japan, where he starred for the Central League’s Hiroshima Carp.

“Since baseball is the only thing I know, I can’t say there’s no chance of that happening,” he said. “But that’s something I won’t know about until after the season.”

Unlike last season, Kuroda has been finishing this one at a strong pace. In 2013, he posted a 3-7 record with a 4.25 earned run average after the All-Star break, and Yankees manager Joe Girardi has made it a point this year of giving the right-hander extra days of rest whenever possible and keeping a tighter rein on his pitch counts.

“Last year was unusual in that I worked an amazing amount, too much, in the first half,” Kuroda said. “I pitched in so many close games and used up so much of my physical strength. So when it came to the second half, I could sense the effects of that.”

“Of course, at this stage of the season, with the Yankees, a team that is expected to compete for the championship every year, you have to step up and treat these games as the most crucial.”

“To be able to make every start for the entire season is tough. You can’t really take a break so that you’ll have something extra for the end of the season, because you can’t disrupt the starting rotation. For that reason, it’s always difficult to be at your best in the second half.”

Despite his age, Kuroda has been the only Yankees pitcher to remain in the starting rotation this year since opening day and on Sunday passed 3,000 innings pitched in his professional career, including 1,304-1/3 since moving to the majors with the Los Angeles Dodgers in 2008.

While an ace pitcher in Japan, Kuroda said it was his habit each spring to air it out at least once in a “nagekomi” bullpen session of around 300 pitches. While Daisuke Matsuzaka blamed the Boston Red Sox’s ban on nagekomi for his arm troubles in the United States, Kuroda said he easily junked the practice when moving to the big leagues.

“Nobody ever said it’s prohibited,” Kuroda said. “But I came to pitch here and thus it was natural that I do things the way they do them here. I don’t even do it all now.”

“I think it was just something you live with. I understood my context was different and within that context I was resolved to do the best I could. The way of thinking is completely different here, and it only follows that if you’re going to really come over here and get it done, that you have to do it all the way.”

Although he said his two-seam sinking fastball is still the center of his game, his approach has changed — as much because of his age as the different challenges major league hitters pose.

“In Japan I was more of a pound-the-zone, overpower-batters-with-my-fastball, strikeout pitcher,” he said.

“In America there are a lot of pitchers who throw harder than me, a lot of pitchers with amazing pitches, so it was a matter of finding a place in American baseball where I could exist, finding a version of my style that worked here as quickly as possible.”

“Some of that is how you use the ball. If you don’t strike out lots of batters you can potentially keep your pitch counts down and work more innings.”

Yet, the biggest challenge came in the context of a 162-game season over a shorter span of time played over four time zones with fewer days off between starts.

“It wasn’t particularly a surprise, but the effort to work 200 innings without injury (was the hardest),” he said. “The meaning of 200 innings is that is a prerequisite to be considered an ace-caliber pitcher. Unlike Japan, a starting pitcher in the majors is with the team all the time on every road trip and be on the bench through every game.

“In the majors, with the jet lag and time differences, it really struck me how hard it is to do that here. That first year was the most exhausting.”