Children and adults alike will be out to show how tough they are as they brave the muddy courses of the Tough Guy and Gal Challenge.
The junior Tough Guy and Gal Challenge is today with more than 1800 kids from more than 45 different schools taking part.
About 1200 children took up the challenge last year.
The first of the adult Tough Guy and Gal Challenges is tomorrow with about 1200 adults taking part.
There is also a corporate and gym challenge tomorrow, with gyms, boot camps and companies taking on the event together.
Next Friday is the secondary schools Tough Guy and Gal Challenge with more than 1000 students registered to take part
These students can gain NCEA credits at this event.
Then, next Saturday is the very last Tough Guy and Gal Challenge for 2017, which also holds the MOA New Zealand Championships - a competition for the 12km competitors who have won at previous events and get invited back to this event, taking on each other to try and become the New Zealand Champion for 2017.
Event Promotion Ltd marketing manager Aimee Gregory says the numbers are great for 2017 in their junior and secondary school events, with good growth in registrations.
She says it is cool to see children and teenagers getting out in an environment that most have never been in before.
The adult registrations are around the same as last year, she says.
"Our target this year is [to raise] $50,000. We are already over this amount and we still have four events to go, so we have smashed it which is awesome."
Proceeds from the annual events go to Cure Kids.
"Our Tough Guy and Gal events are for anyone and everyone - all shapes and sizes and fitness levels. It is just about getting out there and having fun."
She says most people have never done anything like this, so it is a chance for them to push themselves outside their comfort zones.
"I love putting on these events and seeing the smiles on the kids, students and adults faces.
"The atmosphere is always pumping and you can just tell everyone is there to have a good time and that they are. It is just a fantastic event to be a part of."
The junior and secondary school events are sold out.
For the adult events people can enter right up until the day of the event. There are on the day entries at registration - $80 per person, cash or cheque.
This year is the Tough Guy and Gal Challenge's 15th anniversary.
Rotorua is the home of the event, starting in Rotorua with just over 400 competitors to now having more than 20,000 competitors across the series.