Women may be more agile behind the bar because their hips are wider, but often their chests can be a problem, adding to back woes, according to Dunkel.
"Carrying three cases of beer up and down the steps, meandering around people who are wasted, it's so tough on my body," she said. "You torque one wrong way with a case of beer and your knee is shot."
Some days she'll work a 4 p.m. to 4 a.m. shift then go out partying afterwards.
"I rarely get sleep -- only four or five hours a night," Dunkel said. "But it's an adrenaline rush and it's fun, even though it's serious business and I have responsibilities."
Jeff Isaacson, managing partner of Gerber Group, which runs 28 upscale bars worldwide, said today's customers are more demanding than ever.
"They are paying the price and they expect the service," he said. "And that's what we are about."
"People come in to celebrate, to sulk," said Isaacson. "A bartender is a little bit of a psychologist. You have to be able to read people pretty quickly. Some want interaction and others want to be left alone."
"You have to be able to take criticism and insults and be able to understand verbal abuse," he said.
"For me, it's the shake," he said. "If you don't shake correctly, it ruins your back alignment."
Physical therapists say that shaking a cocktail is similar to the motion of a baseball pitch or a tennis serve. Mixing 200 to 300 cocktails a night can be grueling.
But so can the theater that bartenders must perform.
"The hardest part for me is having to be on," said Fernandez. "People come into the restaurant and expect you to have energy about you and make them feel comfortable...This is your performance, and even if you don't want to talk to anyone, you have to be on."
The customers can also be part of the physical challenge. One of his regulars had a disagreement with a lady at the bar.
"He was the sweetest guy, but he was so mad he picked up his glass and smashed in on the bar," said Fernandez.
"I was treating this lady so nice and she ruined one of my guest's experiences," he said. "She got loud and I kicked her out immediately. I didn't even give her the check."
But Fernandez said bartending has been his calling and he can't imagine doing any other kind of work.
"I read about a gentleman who works in the premier hotels -- at the Waldorf Astoria -- and he's been there for years," he said. "He's put his kids and grandkids through school and supported his family. I look up to these guys."
In the end, bartenders say the lifestyle, and especially the generous tips, make the job worthwhile. Some earn upwards of $500 a shift or $2,500 a week, and that doesn't even include their hourly wage, according to Fernandez.
Master mixologist Moreland, an Australian who trained as an engineer before coming to the United States, said that's what lured him to the profession.
"I jumped behind the bar and made more money in a week than an engineer in a month," he said. "And I had a much better time."