I'm sitting backstage with the Broadway singer Jarrod Spector, and he's warming up for a show.

"We are in my dressing room at the Stephen Sondheim Theater on West 43rd Street, right near Times Square," he says.

Spector just got a Tony nomination for his role as Barry Mann in "Beautiful: The Carole King Musical." And right now, he's running through a few warm-up exercises — a half-hour routine he does before most shows.

"As long as I'm good and warmed up, I can sing anything in my range ... including falsetto," he says. He sang a lot of falsetto in his six years playing Frankie Valli in "Jersey Boys."

"It's a relentless, never-ending task to take care of your body so that you can hit those notes day after day after day," says Spector. "Because if you do anything the night before, going out and drinking, screaming, if you get sick, anything that takes away, say, the top 10 percent of your range, well you're out. That's it. You can't sing it. You have to be in the utmost health at all times to sing a role of that difficulty.

"After a while, you learn what your personal limits are. I would struggle with something like acid reflux, so I had to make sure I didn't eat too close to bed. But having a glass of wine at night, a couple nights a week, certainly not a problem."

And regular check-ups at the doctor are a must.

"I'd rather go, and they tell me I'm fine," he says. "And when they tell me you're not fine, you have to take a couple days off singing, then I do."

But Spector's routine isn't necessarily the norm among Broadway singers.

"Only about half of them warm up. I mean, again, these are high-level vocal athletes that go on a stage relatively cold," says Ryan Branski, the associate director of New York University's Voice Center, a place where some Broadway singers go when they hurt their voices.

"We just looked at 25 vocal folds this morning."

Vocal "folds" is the anatomical term for vocal cords.

"We can place a small camera through your nose or through your mouth and take a good look at your vocal cords," Branski continues. "In health, they're nice and shiny, kind of pearly white. They're pliable and loose and floppy. But then, when the system breaks down, you get bleeding or bumps or lumps — there's kind of a whole gamut of things that can happen.

Drew Gehling plays Bob Gaudio in "Jersey Boys," but he found himself at the Voice Center when part of his singing range disappeared.

"I had a vocal injury a few years ago that I thought was essentially going to end my career," Gehling remembers.

He was diagnosed with a mild stiffening of one of his vocal folds. During that downtime, Gehling surveyed 135 of his fellow performers — both lead and ensemble — about their habits offstage. He asked "a slew of questions, regarding their warm-up habits, their cool-down habits, their alcohol intake, their sleep, caffeine intake, the difficulty of their shows and jobs."

He and Ryan recently published the survey in the "Journal of Voice." And the results weren't quite what they expected.

"You would anticipate that the vast majority of them live a rather kind of boring life outside of the theater, and that's not at all the case," Gehling sayd. "Alcohol consumption across all of the performers was greater than 90 percent."

He also discovered that a quarter reported using illicit drugs, and a tenth said they regularly smoked cigarettes.

"This really is a truly gifted group of performers that can get away with a lot and maintain an incredibly high level of vocal health," says Branski. He's implying that they injure their voices a lot less than other high-risk professions, like teachers and telemarketers.

"Teachers have a drastically higher rate of vocal injury when compared to these guys that are doing eight shows a week."

So what's the secret?

Branski smiles and says: "That is a great question that I'm not sure that we have an answer to right now. I mean, you know, biologically, if you were to cut off my head and cut off Drew's head we'd probably sound exactly the same. I mean the source, our larynxes, are probably engineered relatively similarly. But he can do things with his voice that, frankly, I can't. They really are mutants. They're high-level athletes."

And according to Gehling, who is now a pre-med student in addition to his full-time career on Broadway, injuries can be both terrifying and inspiring: "It's a scary thing to go through, to suddenly be faced with not being able to do what you do anymore. And I feel like medicine is about helping people, and making people better — and that's what I want to do."

When singers like Drew do end up at the Voice Center, the operating room isn't the first stop.

"We have folks that come in that are doing eight shows a week that are really struggling," says Branski. "And we see that there are architectural changes to the vocal folds, and so we're on the fence — is this something we need to consider taking a day off, or pulling out, or considering surgery. And a lot of times we can send them to Brian."

He's referring to Brian Gill, the director of vocal pedagogy in music and performing arts professions in the Steinhardt School at New York University. Gill helps singers work through minor injuries, by teaching them to sing more safely, which starts with a little physics.

"So the vocal folds are down in the larynx in the neck. So the airflow coming up from the lungs makes them vibrate. But if there's too much resistance there, the tissue will have increased friction, and friction's the enemy of that tissue," Gill says.

Think of how friction causes callouses on your hands or feet — the same can happen to your vocal folds. You want to minimize that friction.

"So you do things that are called, in Nerdville, semi-occluded vocal tract postures," Gill says with a laugh. "So one of the most popular is the lip trill. When you have this buzz going at your lips, you've actually created a resistance at your lips, which reduces the amount of pressure that falls across the vocal folds. So you kind of get the instrument going, get the muscles coordinated, you become more aware of the resonance, you become more aware of the breath energy. If they were pressing on their voice, that would be bad. And then they get used to the flowy feeling that is — yeah — more efficient, and they try and reproduce that in the show."

But aside from that "flowy feeling," there's another trick performers can use to belt louder, without hurting themselves: singing the right vowel sounds in songs.

"The vocal tract, the way it's shaped, has a certain pitch, or pitches at which it resonates best. I'll give you an example of 'ee eh ah oh ooh,'" says Gill.

He flicks his throat, as he mouths those vowel sounds, producing a hollow resonance on each note.

"When I shape those vowels, there's a particular pitch in there. And those pitches line up with the information that's coming from the vocal folds themselves," Gill continues. "And when they interact positively, you can get a really good boost of sound. You can also get a really belty sound if you hit the right resonance of the vocal tract with the right harmonic from the vocal folds. But, in actuality, you're not working that hard."

Frankie Valli used that trick to his advantage, as did Jarrod Spector — the guy who was warming up at the beginning of the story — when he played Valli in the musical "Jersey Boys."

"There's a song 'Working My Way Back To You' in 'Jersey Boys,' and if you try to sing 'Working my wayyyy back to...,'" Spector says, stopping halfway through chorus. "First of all, it doesn't sound right. It's completely out of the style. But you know also I was just having ... How did Frankie sing it? He doesn't say 'way,' he says 'weh,' so it's 'Working my WEH back to you babe.' And you hear the word 'way' because you know what it is, but it's so much easier to sing, and so much easier to sing that high note."

Voice coach Brian Gill says you can also hear that vowel change in the tune "Astonishing" from the musical "Little Women."

"At the end, the character sings 'Astonishing,' but they actually never sing 'Astonishing,'" Gill says, "because if they did, it would tune in a way that would sound too disconnected. So they always sing 'AstonishAAAAAAAng.' That way they can get a belty sound.

"If you live in a society where, in music theater, everybody's supposed to be able to do belted songs and gospely screams, then finding what you can do sustainably is the key to a really long career."

As is taking good care of your instrument — the voice.

"I find that a lot of my castmates are always like: 'Wow, you're so diligent with your voice.' Yeah, because I want to sing tomorrow!" says Jarrod Spector. "When I go out on stage, I don't hold back. I sing full out every single night."