CrossFit, which originally started in the US, was a fitness program which aimed to offer constantly varied, high intensity, full-functional workouts.
Its international website states that CrossFit offered "an alternative to the prevailing commercial gym establishment and its signature "big-box," machine-based, bodybuilding approach to fitness".
Ellis said CrossFit training focused on building strength, primarily through body-weight exercises.
"The exercises have application to the stuff you do every day, like lifting a box or bending over. We're just training the body to do what's it meant to do."
There were now around 4500 CrossFit affiliates worldwide, and growing.
Ellis said when he started CrossFit New Zealand, in the suburb of St Johns, he had no idea it would become so popular.
"We didn't see it coming at all. We thought we'd be the only ones but it's just taken off."
Ellis' gym had grown from about 30 members in its first year to nearly 200 on its books now.
At another Auckland gym, Ludus Magnus, members can be seen clambering up ropes hanging from the ceiling, running hill sprints carrying medicine balls, and smashing tyres with sledgehammers.
Owner Joe Naufahu said Ludus was "a hell of a lot more fun" than the usual gym and offered "a completely different training experience to anything else".
"We sell the training experience rather than the workout."
Former professional rugby player Naufahu thought the growing popularity of new training methods was a natural progression back to doing the basics, rather than using sophisticated gym machines.
"People are realising that a lot of these machines are just there to make you lazy and make things easier."
His trainers now included the likes of former kiwi-league legend Reuben Wiki and professional mixed martial artist Rod McSwain.
The training was tough but if you made it through the first session, you would probably keep coming back, Nuafahu said.
'Ludians', as members called themselves, were encouraged to "unleash the inner gladiator" as they worked through hour-long sessions written up on a blackboard.
Naufahu said the gym's numbers had steadily grown since he and co-founder Philipp Spahn started the gym about two years ago.
After finishing up in rugby, Naufahu spent a year as a personal trainer at a conventional gym before looking to re-create a team training environment.
"Coming from playing in teams my whole life, I know that with teams, you just feed off each other. Ludus is about helping each other out rather than competing."
Ellis said he also worked in a conventional gym before starting CrossFit.
"I tried for years in a commercial gym environment to help people and I'd spend hours writing these extensive programmes, only to come in the next week and find them doing bicep curls and bench presses."
Club Physical chief executive Paul Richards said he saw both the good and the bad aspects to gyms like CrossFit.
"Obviously they're competitors, but I like them because they're helping people get fit and they add colour and spice to the industry.
"It's radical and fun but it's really for very fit people. It's definitely not for the average person."
Richards estimated that around 90 per cent of New Zealanders could not survive the type of high-intensity training at CrossFit or Ludus.
He also said some of the exercises were not wise.
"If you do what I've seen them do and you already have a lower back injury, you could wipe yourself out straight away."
Ellis said he agreed that there was potential for injury, especially if a gym was set up by "cowboys".
"For some people, if they've been very inactive, then more care needs to be taken with them."
But he said all new members at his gym were taken through an intensive introduction process.
"It takes people a month of basic training before they can start the main classes."
There were always trainers on deck to monitor people's form and technique, he added.
Prices at gyms like CrossFit and Ludus Magnus tended to be much higher than conventional gyms. ranging from $180 to 300 per month.
"It's a heck of a lot more expensive than somewhere like Jets, but there you don't talk to anyone and there's not much room," Ellis said.
"We like to think of it as cheap personal training. Most of the time with a personal trainer you can't really justify the cost. People are better off sharing the costs with a bunch of people."
Richards thought the rates that CrossFit charged were about right.
"Our gyms in New Zealand are far too cheap. I think good on them.
"And the funny thing about it is their facilities are very basic so it should be the other way around but we can't increase our prices because our competitors aren't."
*There was an error in an earlier version of this story which has been amended. The final quote incorrectly used the word 'drop prices' rather than 'increase prices'.