Chronic asthma is a motivator not a barrier to competing in the Ironman New Zealand, Alistair Harsant says.

The Glenfield father of one plans to swim 3.8 kilometres, bike 180km and run 42km in Taupo next March in his quest to raise $10,000 for the Asthma Foundation.

It will also mark his 40th birthday.

The former New Zealand representative triathlete says the sport has been the best cure for his asthma.

"It's the most fantastic feeling to know that something that used to have so much control over me doesn't anymore," Mr Harsant says.

"It's the combination of swimming, cycling and running that's made the biggest difference in my wellbeing."

Inspiring others with asthma, he says has driven him to take up the challenge.

"If I can do it, why can't they?"

An asthma attack at just 18 months old was the first sign Mr Harsant would spend the rest of his life with the illness.

"I spent a lot of time in hospital; at one point the coughing was so bad I was getting double hernias in my abdomen. I don't remember a lot of my childhood because of it," he says.

With limited treatments and knowledge of the illness, Mr Harsant had to contend with severe asthma attacks and allergies throughout his youth.

"One of my mother's early techniques was to hang my body upside down over the end of the bed and tickle me until I was coughing and spluttering. That seemed to do the trick," he says.

Mr Harsant tried to lead a normal childhood, despite asthma casting a shadow over everyday activities.

"I remember in the middle of summer, it was stinking hot and I had to wear heavy cotton shirts to keep my chest warm.

"Other kids were all running around in T-shirts, so I unbuttoned my shirt and I got a big telling off from the teacher."

It wasn't until high school that he discovered sport could be an asthma therapy, not just a trigger.

He has competed in half-ironmans and triathlons, including the ITU Triathlon World Championships in Honolulu seven years ago.

"If you find a sport you enjoy, then you'll get out and do it. All the deterrents rain, fatigue and even asthma will become insignificant."

Go to asthmafoundation.

org.nz/support-us/get-involved/ironman-for-asthma/ to support Alistair Harsant and the Asthma Foundation or go to facebook.com/pages/Ironman-for-Asthma/190616047722928.

- © Fairfax NZ News