Actor Arnold Schwarzenegger turned personal trainer to help his friend Tom Arnold lose weight.

The 54 year old has lost 90 pounds (40.8 kilograms) since last year (13) and credits his True Lies co-star with helping him to achieve his goals by working out with him in his luxurious gym.

He says, "If Liberace had a gym - it's like a Versailles - there's columns and statues and paintings of his family.

"You go in there, he's got a lot of his buddies, they're European. They got their shirts off and G-strings on... and they wear the real short shorts."

Despite the unique gym experience, Arnold insists Schwarzenegger is looking out for his best interests.

He continues, "He really cares... He means well, but it's very intimidating. By him just looking at you when you're working out, you feel very insecure... He jams his big meaty finger into your belly."