Broncos behemoth Payne Haas has credited tortuous runs up a steep kilometre-long bushland hill as a youth for creating the massive motor he now possesses.

In the pre-season, a cavalcade of Broncos stars lined up to wax lyrical about the extraordinary engine of the 18-year-old in training drills where his endurance and hunger for hard work had the likes of Alex Glenn, Sam Thaiday and Korbin Sims awestruck.

Glenn called Haas "no pain" after watching the 194cm and 120kg giant motor on and on, and on, during one session.

Haas's Keebra Park High schoolboy coach Glen Campbell also told NRL.com about the prop's extraordinary "VO2 max", an athlete's capacity to perform sustained exercise, and how he had not come across a big young forward with such durability.

The question that remained unanswered was why Haas was out of the box in this regard but now the man himself has shed light on the mystery.

"It all comes from my dad [Greg] just training me hard," Haas told NRL.com after helping Wynnum-Manly beat Norths Devils in the Intrust Super Cup.

"We had acreage on a house near the Gold Coast and there was this massive kilometre-long hill that we used to run up and it was really steep.

"Dad used to make me run up it. I would have run up it a hundred times when I was 12. It was all bushland and it was hard going, but it made me mentally tough and who I am right now.

"My big brother Jonah was my training partner and he would push me to my limits. Dad said fitness was the number one priority for me coming into footy. I've got a big body so I've got to be fit. I was mentally ready for [the Broncos pre-season] because Dad put all that into me."

It wasn't just his old man and his brother that were cracking the whip on a young Payne. His mother Joan was also a tough taskmaster.

"Mum was real hard on me too," he grinned.

"Dad was the one who trained us but Mum would get in behind us and get up us if we weren't giving one hundred per cent.

"I remember when I was younger I'd get called over at half-time and Mum would give me a little spray and tell me to get on with it."

Greg has Swiss and Filipino heritage and Campbell had speculated in the earlier NRL.com article that Haas' endurance might be a hereditary thing - perhaps there were some long-distance skiers from the Swiss Alps in his ancestry, he mused.

"My dad was a national hurdler and was supposed to be the next big thing in hurdles but injuries got the better of him," Haas said.

"He went to the Pan Pacific Games as a young kid and was one of the best in Australia at the time but he had hamstring problems."

When you play in the Broncos kit it makes you proud to be a Bronco. I just want more of that, and I can't wait for it. Payne Haas

Haas is still in his development phase, playing Intrust Super Cup with the Wynnum-Manly Seagulls.

Last month Broncos coach Wayne Bennett told NRL.com that a crop of young forwards, which include Patrick Carrigan and Thomas Flegler, would reap the benefits from playing in the Intrust Super Cup and not the now defunct national under 20s competition.

Haas said he was learning plenty playing for the Seagulls."It is good for me because I am a young body and I have to get used to the contact with men and get used to the physicality," he said.

Haas impressed in the pre-season trial for Brisbane against the CQ Capras and can't wait to don the Broncos jersey again.

"It was awesome to get a taste of it in the trials and it just makes you more hungry," he said.

"When you play in the Broncos kit it makes you proud to be a Bronco. I just want more of that, and I can't wait for it."