How do you play in more than 400 consecutive NHL games? Let’s start with this: You have to be tougher than a hunk of week-old Bubble Yum. Uh, right?

“No, definitely you’d never say that I’d be considered tough,” disagreed Caps defenseman Karl Alzner, who Thursday night played in his 419th straight game.

So what else? Presumably you’d need to be fanatical about your body?

“I like to think that I work hard, but I don’t always eat as good as some of these guys or train as good maybe as some of these guys,” said Alzner, who now stands just three games away from the franchise mark for consecutive games played.

Maybe you need to be a good ol’ Canadian farm boy (“I’m just a suburban kid, pretty much,” Alzner said), or someone who never gets sick (“I’m no better than the next guy,” Alzner said of his immune system), or someone who’s in bed by 9 every night (“If there’s a good show on TV or I’m stuck in a crossword or a game of Monopoly or something, I’m going to play ’til it’s over,” he said).

Alzner — who scored his third goal of the season in Thursday’s 4-1 win over Vancouver — hasn’t missed a game since October 2010. He’s working on the seventh-longest consecutive games streak by an NHL defenseman since World War II. He has played far more consecutive games than any National (no one played 162 last season) or Wizard (Ramon Sessions leads the way with 76 straight), despite regularly throwing his body in front of vulcanized rubber and colliding with opponents in unforgiving corners of the rink. He’s third on the Caps in average ice time this season, and recently upped his minutes despite playing through a host of maladies. How has the 27-year-old done it?

“Luck,” Washington’s longest-tenured defenseman explained. “Honestly, it’s all luck.”

Well, maybe. But luck is winning the lottery by choosing RGIII as your Powerball number, hitting an inside straight on the river, or rolling snake eyes after landing on Park Place. Not missing a game in more than five years would seem to involve at least a few things other than happenstance.

“A lot of grit, a lot of guts,” teammate Brooks Laich said. “Being accountable to your teammates is very important to Karl. Showing up every day is very important to him. Being consistent every day is very important to him, and the game is very important to him.”

“It’s toughness; it’s some luck; it’s good genetics,” Coach Barry Trotz said. “I’ve got a lot of admiration for Karl. Because it’s like death and taxes: You know it’s coming. I know he’s out there every night.”

(And yes, writing about this streak three games before it enters the Caps record book constitutes a horribly unhockey-like flirtation with jinxiness. I knocked on wood before leaving Alzner’s stall. He knocked on his teeth. Please add whatever gesture you feel is appropriate.)

Alzner’s streak managed to remain under wraps for most of its duration, because he was forever two games behind John Carlson, his fellow blue-liner and close friend. Carlson’s longer streak finally ended at 412 games last month, leaving Alzner to close in on former Caps center Bob Carpenter by himself.

Carpenter played in an era before “upper body” and “lower body” injuries. When he was playing through pain in the early ’80s, it was because of a separated shoulder (he wore a brace with a strap under his sweater) or a broken foot (“You really couldn’t walk at all, but once you got it in the skate and you tied it up, it felt fine,” he assured me.) Carpenter, like Alzner, said he never set out to create an endurance streak, and that some of the factors — lineup choices, physical capabilities — were out of his control. Still, 400-plus games is 400-plus games.

“A great accomplishment for him to be able to do that,” Carpenter said. “Just to be able to play 400-some games in the NHL, to be in the lineup game-in and game-out is awesome for him.”

A few weeks before Carlson sat down in late December, Alzner’s streak also appeared in jeopardy. A potential replacement was recalled, and for about three weeks, Trotz went to head athletic trainer Greg Smith just about every morning to ask if Alzner would be okay to go. “We’ll get him ready,” Smith said each time. Alzner kept playing.

“He’s been hurt badly this year, and continued to play,” Trotz said Thursday. “I know Karl’s starting to heal up, but he’s been banged up for a long, long time, and he keeps rolling.”

Have the injuries convinced Alzner to dial down his intensity in order to preserve his health? Consider last Saturday’s trip to Manhattan: Alzner blocked seven Rangers shots, including one leaping effort when he flung his exposed back and head into the path of a wrist shot. Forget the consecutive games streak; that seemed like a poor way to last consecutive minutes.

But this is what Alzner does. He has blocked 115 shots, 40 more than his closest teammate (Carlson). In fact, he’s seventh in the NHL in blocked shots since his streak began.

“I don’t want to block them with my back or with my head,” he said. “But it’s something that I feel is necessary sometimes — to go and find a way to get it to hit you — and that was one of those times. … If I do that and nothing happens and no one’s hurt and the puck stays out of the net, then it’s no big deal.”

Alzner’s blocked shots aren’t the only stat line he has increased this season. He promised in the preseason to be a more physical player, and he’s on pace to break his career high in hits, which he set last season. That effort, he said, is about perception as much as anything: letting opposing players know that “if they’re going to come into your corner, they’re at least going to get either hit or cross-checked or something like that, just so that it’s not an easy night.”

And this is perhaps the biggest paradox about Alzner’s streak. It’s a mark of grit and toughness and perseverance, from perhaps the kindest athlete in Washington. Alzner said he doesn’t enjoy crunching body checks because “that’s not the type of person I am,” that he is playing a more physical game now because “you do what you have to do to win.” He said he sometimes feels bad when he lands a potent hit, and that “there’s guys who have more edge than I do; I wasn’t born like that.”

He was born with enough edge, though, to play through more than five seasons of bruises and cuts and aches, more than 400 games at one of the most grueling positions in one of the most physical sports. If you’ve knocked on enough wood, Alzner will equal Carpenter’s mark Tuesday in Columbus, and surpass it next Friday against his former coach Bruce Boudreau. Despite his conviction that this is a mark of chance more than skill, Alzner would accept his place in history.

“In all honesty, it’s probably the only opportunity I have at setting any sort of record, you know?” he said. “I’m not going to get the most points or score the most goals. I’m not going to get the most penalty minutes. It would be my only chance. So thinking of it that way is kind of cool. But it’s not how I’m going to sum up my career when I’m done.”