By now, you probably know the story.

Masahiro Tanaka threw 160 pitches in Game 6 of the Japan Series for Rakuten this past November. He then came back the next night and got the final three outs in relief to save Rakuten's series-clinching victory.

It's the stuff of legends.

It's also the source of the Yankees' biggest concern about the pitcher they signed on Wednesday to a seven-year, $155-million contract: Will Tanaka's heavy workload in Japan cause him to be less effective in his major-league career?

Remember, this is a 25-year-old who has never thrown a pitch in the big leagues, and the Yankees gave him the fifth-largest contract ever for a pitcher (and will pay Rakuten a $20-million posting fee).

But Tanaka has thrown thousands of pitches in Japan ever since he led his high school team to that country's national championship as a junior in 2005.

"You always have concerns," Yankees general manager Brian Cashman said this past week when asked about Tanaka's workload. "I think I can speak for anybody. That's something you can't ignore or deny. But despite that, clearly, by the competitive bidding on him as a free agent, with his age, talent and the scouting assessments and the pitching market the way it is, the available pitching -- it's certainly something that we were willing to take the risk [on]. Despite acknowledging, yeah, there's a workload there."

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There are many unknowns about how elite Japanese pitchers will perform in the major leagues. Adjusting to a new culture. Facing much better competition. Throwing a different ball.

"There is risk with pitchers from Japan that I have certainly spoken to," Cashman said. "The ball is still different from a major-league ball. The workload is different, because they pitch every seven days, versus five days over here. Strike zones are different. The lineups are different.

"There's a lot of risk associated with working through those variables . . . But at some point you still have to make a call and make a judgment. We obviously believe in this player's talent."

But what about his durability? How a young pitcher's workload will affect his prime years is something American baseball has been grappling with for years. Pitch counts and innings limits are as much a part of the conversation as hits, runs and errors.

"How many pitches has he thrown?" is a commonly heard question -- and an easily answered one at the stadium because the pitch-count tracker is so readily available. That wasn't the case 30 years ago.

Nearly all teams practice injury prevention by limiting the workload of young pitchers. That is not so in Japan, where high pitch counts are the norm.

Tanaka threw 1,315 innings in seven seasons with Rakuten, an average of nearly 188. He threw 53 complete games, which is three fewer than new Hall of Famer Tom Glavine had in a 22-year career. As a teenager for Rakuten, Tanaka threw 359 innings. In high school, he once threw 742 pitches in five games in a national tournament.

Not everyone thinks the 6-2, 205-pound Tanaka will be ruined by the heavy early-career usage. Former major-league third baseman Marty Brown, who managed Tanaka in 2010, said pitchers such as Texas' Yu Darvish, the Yankees' Hiroki Kuroda and Seattle's Hisashi Iwakuma understood how to prosper in the Japanese system before leaving for, and succeeding in, the U.S.

"You always question yourself -- can this guy do it on four days' rest?" Brown said. "But really, what I've seen out of the real good ones, Kuroda and Yu Darvish, Iwakuma, all of them can do it. I think they take advantage of the Japanese system, quite frankly. They want to pitch on Sunday when it's you vs. whoever the No. 1 pitcher might be for another team.

"If you're going to pitch once every week, then by all means throw 170 pitches. I'm good with that. You've got all those days to recuperate. But if you're pitching on four days' rest and I'm going to have you back there on the fifth day, I'm not going to let that happen. Because you're going to break. Tanaka, with his frame, he's probably stronger physically than a lot of the guys I've mentioned."

One thing is certain: The Yankees will never ask Tanaka to throw 160 pitches in a game. If he is to build a legend in pinstripes, he will have to do it in about 100 pitches. And he'll get the next day off, too.

With Jim Baumbach