They're bullishly self-assured - to do what they do, they have to be - and they're not above making an audacious claim or two.
As Alison Storey, New Zealand's No. 1 personal trainer for two years running, says: "We are the magic bullet that can save the planet."
Now, that's a big call. But she's tough enough to make it. Storey, a New Zealand representative in three sports, seriously believes her profession can help solve the western world's health woes.
"We have the answers to diabetes, obesity, bad nutrition - all those things," she says. "But I don't know how you make personal training a more respected profession."
Well, they're often in the news. Tame Iti had one; Adele has just got one. World champion hurdler Jana Pittman has just become one, to fund her bid for the 2016 Rio Olympics.
And they're not hard to find. There are just over 1000 registered personal trainers in New Zealand and around 500 more who aren't signed up to the non-compulsory national Register of Exercise Professionals.
And there's plenty of evidence out there, too, that many of them have transformed people's lives.
As the name tag suggests, their interest in your fitness is a lot more personal than a regular gym instructor. They specialise in prescribing the right exercise regime for each individual and urge them on to their goals - while extracting bucketfuls of sweat and tears and anywhere between $60 and $90 for a 45-minute session. Good PTs will give their clients advice on nutrition, too.
Says one personal training convert: "Personal trainers used to be the domain of bored Remuera housewives. But now there are a lot of people who want to learn to exercise smarter."
Motivation is the major selling point for PTs; most of us struggle to drag ourselves to a gym. Around 420,000 Kiwis, or 12 per cent of the population, belong to a gym or fitness centre - but being a member and actually using the equipment are two different things.
"My entire business exists because 99 per cent of people are not self-motivated enough to do it; it's just the way it is," Storey says.
"I say to people 'don't ever berate yourself for getting me on board to help you. You're smart, you realise you can't do this by yourself, so you've gone and found the resources to help you do it'."
Others, who get themselves to the gym but wander aimlessly between fitness machines, look to PTs for guidance and incentive. Some want to lose weight, others want to gain muscle to flex on the bodybuilding stage. Whatever the reason, personal trainers will put their clients through high-intensity workouts so when you want to give in to the hurt, they make you push on through it.
"They tend to care about you as a person too," says another regular PT user. "Before the weekend, my trainer sends me a text saying 'Don't forget to wear your sunscreen!"'
Alison Storey parks her Honda Odyssey outside a suburban house in Cambridge - "the town of trees and champions" - prepared to inflict pain on the home's inhabitant.
Inside the people mover is her arsenal of weapons - swiss balls, hula hoops, dumb bells and skipping ropes; a couple of wooden step boxes her husband knocked up for her. "You don't need big, flash equipment," the personal training guru says.
She's been known to make her clients throw up on their swiss balls and doesn't hide the fact that she's a "hard arse".
"I've gathered a bit of a reputation. I don't have time for people who say 'I walked to the shops at lunchtime today, so that was my exercise'. No, that was a mode of transport. You have to puff and sweat and pump weights, there's no way around it," she says.
Storey blames her genetics and the environment she was raised in. Her father, Dudley Storey, was a champion rower, a gold medallist in the coxed four at the 1968 Mexico Olympics, and she inherited his work ethic.
"My father instilled in us that you sweat and you rest: eight hours' work, eight hours' play, eight hours' sleep. That's been such good advice. Loads of personal trainers do that really wrong, I reckon. They burn themselves to a frazzle and forget that no one's training is as important as theirs.
"Why is anyone going to visit a trainer who is tired and unenergetic?"
Storey rises at 5.30am to do half an hour's training before taking her time over breakfast and the newspaper: "I read to learn; that's my play time."
She operates her mobile personal training business during the day, and trains again in the evening. She's in bed by 8.30pm.
"I need to be productive. I need to feel like I'm adding value to the world, every day that I'm here," she says.
Storey was until recently training herself towards this year's London Olympics. A former New Zealand rhythmic gymnast and rower who won Commonwealth gold in 2002, Storey's latest sport of choice is beach volleyball. A month ago she gave up her bid to qualify for the Olympics and is concentrating on her mobile personal training business.
"A lot of people don't want to travel far to exercise, so I take the mountain to Mohammed. And lots of people like to work out in the privacy of their own home; their time is really valuable and they can be working at their desk five minutes before they do their workout. It's an effective use of their time," Storey says.
Awarded the Personal Trainer of the Year for the past two years at the New Zealand Fitness Life Awards, judges said Storey's "belief in the power of the fitness industry to improve the health of the nation is inspiring".
Almost bouncing down the phone line as she speaks, Storey says she believes in sharing her knowledge (she has a degree in exercise science and a graduate diploma in business studies and sport management) to motivate others to achieve.
"I've spent more money and time on my ongoing education than most doctors," she says. "My biggest goal isn't about weight loss so much; it's to make people healthier and fitter to enjoy opportunities that life has to chuck at you."
A PT since 1996, Storey's proudest achievement is helping a woman to walk again. "She had a freakish accident where a disc had poked its way into her spinal cord and surgeons had to rebuild the cord's casing. She couldn't walk when she first called me in, so we started with me lifting her foot on to [an 8cm-high] block so she could try to use her muscles to lift it off again."
Eighteen months later, the woman is doing 10-minute shuttle-runs. "I just stood there and told her what to do - she's the one who got stuck in, pushed through those mental barriers to bring her back to this level of mobility," Storey says. "It's like she's been given a second chance. It's blindingly cool, eh?"
When the curtains closed on Anouk Koene's dancing career, she began a meticulous search for "a second passion". But all the while, she was cautious not to step on any toes.
A former cheerleader who danced on the big screen in Sione's Wedding, the professional dancer's repertoire stretched from hip-hop and jazz to cabaret and burlesque. But when the dancing ended, Koene - a fitness buff - was drawn to a new career as a personal trainer. She intitially held herself back, though, worried that she might upset her sister, an exercise kinesiologist.
"Exercise is her career. In the end, I decided it was what I wanted to do too and I had to break it to her. She took it pretty well," she laughs.
A year into her new-found love - with credentials in exercise consultancy and personal training from the New Zealand Institute of Health and Fitness behind her - Koene was crowned personal trainer of the year at the Les Mills Britomart Gym, also in its infancy. She calls it the proudest moment of her life.
The bulk of her clientele are young, professional women she calls "my girls". She writes on her Facebook page: "So it seems I'm building a little army of crazy, strong women. Nice work Kimberly, beating her hubby in full push-ups!"
She trains clients as she trains herself - hard, fast and intense. Five times a week, she does her own 24-minute workout, including 142 full push-ups and 60 burpees.
"It's common sense for a trainer to set a good example. It helps my business and my age as well," says the 39-year-old.
"I think I'm a pretty tough trainer; they know a workout with me will be demanding. Of course, I have to listen to how they want to train, but they generally come to me because they know I'll make them work."
On a busy day, Koene will work with eight to 10 clients, one-on-one, running them through personalised programmes - 45 minutes to an hour of grunt and sweat. "When I first get them in, I make sure they're doing everything with the right technique. A lot of girls need to build strength before getting into a real workout," she says.
"It's a bit of a personality match-up, whether they trust you, or like the stuff you do, so I'm humbled and honoured when people choose me to help them. One of my girls texted me to say she had just fitted into a dress two sizes smaller. I know it's important to give them support even when you aren't with them. They've worked really hard and they've spent a lot of money, so I never forget that."
She takes inspiration from what her girls achieve. "One of them lost 10kg in eight months. She's fit and strong, and it makes me proud. She's on her own now, she got all what she needed from me," she says. "I don't feel like any of it is work.
It's like a big playground - a huge, colourful jungle gym."
If you see Abraham Dyer in a horizontal-striped cocktail dress, beige stockings and heels, sipping a mai tai in an Auckland bar, you'll know he has failed in his job.
The father of one and a former soldier, known as CEO Abe (stands for Chief Exercise Officer), must pay in humiliating ways when his clients don't meet their goals.
At the TomFit Studio, deep in the commercial heart of Auckland's North Shore, Dyer's clients sign a non-negotiable contract. "They set themselves goals and if they fail to meet them, then I cop the punishment," he says.
"For one woman, I have to make her work so hard that her hands shake by the end of a session but I can't let her quit - or spew. If she does, I have to dress in drag and go to a bar in the city and have one drink. She's brought my costume in to show me.
"It's where we've made ourselves different from everyone else."
A dash of fun is part of the programme with CEO Abe, who's adamant it's not all about being a hard taskmaster.
"To be a trainer you have to be a best friend and counsellor, a nutritionist and dietician, an angel and a devil on their shoulder," he says.
The compact studio Dyer helped to set up is dubbed "the anti-gym".
"There are windows but no mirrors. We know a lot of people go to gyms where they don't know what they're doing and they feel exposed and intimidated. We have ladies who, at first, can't fit through the door. So we designed a fun environment."
It was important for Dyer that this place had windows. After serving in the New Zealand Army for nine years, including tours of Afghanistan and Timor, he took a desk job as a gambling inspector for the Department of Internal Affairs. Two years in a windowless office drove him to pick up a brochure in his local gym and decide "personal trainer" sounded more like him.
After training at the Max International Fitness College - an Australian organisation promoting itself as "the world's only private fitness business college" - he was asked to run a TomFit Studio in Mairangi Bay.
Dyer, a finalist in the Up-and-Coming Personal Trainer category of the 2010 national fitness industry awards, runs around 50 sessions a week.
He's also known as a boot camp specialist - no surprise, considering his military background.
Does he miss the army? "I only miss my mates ... and shooting. I don't miss the 'regimentality'."
But doesn't personal training have its own rigid discipline about it? "Only for certain types of people. I have a CEO of a large insurance company who's direct: 'Abe, I want to see my numbers'. Then I have a receptionist for who it's about having a laugh and having fun, as long as she's puffing and sweating."
His clients are many (38) and varied - more than a third are local businesspeople, some are stay-at-home mums. One woman drives down from Whangarei once a fortnight to workout with Dyer, others come regularly from Muriwai and South Auckland.
They all get one-on-one attention, whether it be in boxing, kick-boxing training, bodybuilding, or boot camp.
"We've taken people who are 130kg with diabetes and got them bodybuilding on stage," he says. "My favourite success story is the lady who got divorced after 30 years in a marriage where she was always told she was nobody. She wanted to cycle around Lake Taupo and 10 weeks later we took her down to the lake and chucked her on her bike. She was buzzing - and it was just as rewarding for me to be waiting with a glass of vino at the finish line and say 'you did it'."
Dyer ensures he maintains his own fitness, with his own personal trainer, working to his goal of competing with his Tutukaka waka ama crew in the Molokai Hoe island-to-island race - the world's premier outrigger canoe event - in Hawaii in October.
And he needs to be in shape for the annual fundraiser, Train the Trainer, when his clients buy time to put their trainer through his paces. Last year, on hands and knees, CEO Abe had to crawl across the carpark with 70kg of chains around his waist. "It's payback time, balls to the wall," he laughs.