Arnold had a one year older brother, Meinhard, who died in a car accident when he was in his twenties. They were both raised in a very strict catholic home.

One day after seeing the Olympic swimchampion Johnny Weissmüller in Graz, Arnold was so inspired by Johnny's physique that he decided he wanted to become a champion athlete and started training.

In the early years Arnold and his brother practiced a lot of different sports such as skating, skiing, hiking, swimming and tabel-tennis. Because of the interest in sports the school came in second place and did not get much attention.

The brothers were always competing against each other both in sports and in school. Gustav wanted Arnold to become a world-class soccer player, but at the age of thirteen Arnold dropped out of the soccer team.

He was looking for a rolemodel and found one on the silverscreen, Hercules. He watched all the Hercules movies over and over.
He started to collect muscle magazines and was so impressed by the strength and the muscles in the magazine that he had just one goal clear in his mind.
So he started to train.

In 1961 Arnold met Kurt Marnul, the former Mr. Austria. Marnul was impressed by Arnolds body and asked him if he wanted to train in the Athletic Union in Graz. And of course Arnold wanted that.

Arnold trained seven days a week and for that he had to drop out of school and abandon the church.
Besides training Arnold began a three-year apprentenship as a carpenter. He competed in his first competition in Graz hotel and came in second place. In 1965 he enlisted in the Austrian army, and to compete in Stuttgart Arnold had to go A.W.O.L and for that he was jailed when he came back. But he won the competition and was awarded the title Junior Mr. Europa.