Mountain bikers could face anything from mechanical problems to hallucinations when they tackle the World Solo 24 Hour Mountain Bike Championships in Rotorua.
The annual event is being held in New Zealand for the first time this weekend and is one of the feature events at the Rotorua Bike Festival.
The format of the race will see riders complete as many laps of a 17.3km circuit in the Whaka Forest as possible over 24 hours.
Organiser Tim Farmer, from Rotorua's Nduro Events, said many of the competitors will ride for 24 hours straight without sleeping, and will face plenty of challenges along the way.
"They could face equipment failures, body failures, nutritional issues, the weather can play a part, there is so many variables," he said.
"For a one-day race it is pretty tough."
He said riders may even experience hallucinations especially in the early hours on Sunday morning but it was all part of the challenge.
Farmer said a huge part of the race came down to nutrition and having a good team in the pits.
"They will consume thousands and thousands of calories - many of the riders will bring a smorgasbord with them.
"My wife is doing the race and she has everything from rice risotto to Red Bull and everything in between.
"And you have to start eating as soon as you start. So there is a lot of tactics that are involved."
Defending world champions Sonya Looney (Canada) and Jason English (Australia) are both entered in the race which is set to begin at noon tomorrow.
Farmer said the heavy rain this week should not affect the race too much - with good weather expected this weekend - and the trails drained well.
World Endurance Mountain Bike Organisation (Wembo) president Russell Baker said it was good to bring the event to New Zealand. He said it was a great challenge for riders.
"It is a big ask on the body but it is probably a bigger challenge on the mind, especially when your mind says to do some crazy things at 2 on a Sunday morning."
He said the trails in Rotorua were world famous.
"In the Australian mountain bike magazines they are all talking about Rotorua and how people should go there."
* World Solo 24 Hour Mountain Bike Championships
* Whakarewarewa Forest (17.3km circuit)
* Starts noon tomorrow, finishes noon Sunday