When I finish a few, it feels pretty choice. But then I gaze around the gym and my jaw drops: The regulars are doing handstand push-ups or walking about on their palms in the hand-stand position, looking like scorpions with their legs curved over.
But Darren reckons anyone can do CrossFit. You just scale the movements, reps, loads and intensity to suit your fitness level. So no exercise ever gets easy. And it's not meant to, of course.
Darren is always hovering, detailing the number of reps for each challenge, demonstrating correct technique and motivating individuals to try harder. He jokes: "If I think you can go heavier [with your weights] I'll have a chat to you."
Other challenges include reps with kettlebells, lunges with weights held high in the air, and I also hold myself up on a bar and lift up my legs to the height of my stomach (called an L sit). I see some CrossFitters hold this pose for about 30 seconds, but I could barely handle it for a nanosecond and I'm wheezing like an asthmatic. But each one I attempt, leaves me wishing I could do more ...
Other core holds were done on gymnastics rings (loved that equipment) and the session concludes with a dumbells-based circuit where everyone leaves their small group sessions and gathers in the middle of the room. There, the music blares, the giant clock ticks over on a wall and everyone suffers and sweats together lifting iron.
More than a couple of times through the class I hear clapping and see smiles as someone slams a personal best, or gym record. You kinda get swept up in their success, and want a piece of it yourself. If you do break a record, your name goes on a whiteboard for everyone to celebrate (and aim to beat).
Darren explains there are two sides to his CrossFit clientele: There's the functional, old-school health and fitness regime that suits all sorts from firefighters, cops, housewives and accountants to grandmas; then there's the clients who take it seriously: they're the ripped-body, super-athletes who tackle The CrossFit Games.
At one point I stand next to Krista Sandford-Hill, a sleek 26-year-old radiation therapist, who tells me she felt "dead" after her first CrossFit class, but adds "you feel dead after every class!" She raves about CrossFit as a great toner and "it's addictive".
The motto for CrossFit is "forging elite fitness", because members want to keep aiming to get fitter and stronger. I ask Darren why some call the fitness craze slightly cult-like. He laughs and says it's because when people discover it they really believe in it. They're wowed by their results, and want to tell mates to try it too.
It appears word is spreading. There are already 50 CrossFit gyms nationwide after just five years.
How much? $250 a month for three workouts weekly is Darren's standard membership. Other options are available.
Worth it? I thought this was a bit crazy before I tried it. But now I get it's cool charm: It's effective, fun and there is a friendly and motivating buzz about it.
Try it: Darren's CrossFit gym is at 19 Thomas Peacock Place, St Johns, Auckland.
Rating: 10/10