What is it? Guided group fitness sessions for 50 minutes. You can choose low-impact, or go for the high-energy option.

What's needed? Workout gear, water, sunhat, sunglasses, sunscreen.

The experience: I'm at Mission Bay smelling the refreshing salt air, hearing the waves lap rhythmically on the shoreline and I can feel the late sunshine toast my back as I stare out at that majestic hump that is Rangitoto Island. It's paradise, really.

But I'm not here to soak up the sights, but to soak in sweat at a beachfront fitness session run by the Jetts City Surf Series at Mission Bay. Soon, I'm crimson-faced and dripping wet with sweat.

We kick off with leapfrogging through the sand. I'm bobbing up and down through the grit just like a crazed green and slimy frog would if it were hot-footing it away from a hungry, mean snake.

It's hard enough jumping along solid ground. But doing this exercise in the sand is 10 times tougher as you sink in the grit then have to try to power yourself back out of it again and again ...

It's only a few minutes of leapfrogging but I'm thankful when that punishing exercise ends. It thrashes my glutes and thighs.

At least I'm among good, sweaty company. More than a dozen other "frogs" are with me during this session. Some are here for general fitness, while a few tell me they are here because they want to get fit before trying out for the Army and Navy. I reckon being a frog will be excellent exercise to be fit enough for such noble careers - which tends to be the pathway for future princes.

The leapfrogging is among a number of gruelling exercises that a Jetts personal trainer has our group doing. We also do things like mimic ice-skating in the sand, run to cones, push-ups and burpees.

For those who don't know what burpees are, I'll tell you they're a full-body workout: you begin them standing up, then drop to a squat position with your palms on the ground in front of you. You then jump your feet back so you are in a push-up position. Then you return to the squat position, before returning to being on your feet.

You keep repeating this exercise until the trainer (not you) says you've done enough.

The session finishes up with a friendly game of touch rugby. I catch the ball successfully on the single occasion someone trusts me enough to catch it. The guys are good at this part. Then the session ends and everyone shakes hands or pats each other on the back and says things like, "Good work!", "See ya next week."

It's a friendly atmosphere, and as I leave the workout I look out at the family-type conviviality that is the City Surf Series. There are close to 150 people here taking part in assorted activities in the sunshine while listening to music pumping from speakers.

The series offers a menu of beach-related fitness options, among them surf-lifesaving sessions for little nippers (ages 6-12) and also the popular stand-up paddle-boarding races for adults.

It was quite a sight to watch almost 100 people (mostly "built" blokes) powering their muscles hard to motor along the top of the water at speed.

The director of the series, Troy Huston, says their fastest competitor, Marcus Hansen, did the 4.5km course in 31 minutes and 36 seconds, "which is exceptionally fast".

I would say most of those racers whipped along the water darn fast - much faster than I could leap-frog through the sand ...

How much? Jetts Beachfront Fitness groups are among eight disciplines offered at the Jetts City Surf Series, held on Thursday evenings at 4.30pm and 5.30pm with casual rates of $20 a class. Participants can turn up on the day, or you can sign up online for six weeks for as little as $99, or sign up for longer if you wish. There are 11 weeks left in the series.

Worth it? This would be great to try with a mate. It's motivating fitness out on one of Auckland's neat beaches. But the most popular thing for sure is the stand-up paddle-boarding races. Prizes are available to contest later on in the series too for those with the best times.

Try it: check out more information through citysurfseries.com

Rating: 8/10

- Herald on Sunday