"For Terminator, he wanted to just keep himself healthy while filming. And somehow during the course of him getting ready for Whiplash he wanted to take things to the next level," says Williamson, who notes that Simmons has another trainer in Los Angeles.
"He started to fall in love with the fitness lifestyle. Where I come into play is now that he's at this point we are giving him muscles he didn't have before.
"His motivating factor with a lot of it is to do something with his arms and shoulders to be able to possibly down the road play a character who can wear a tank-top."
And Simmons' secret to achieving incredible rippling muscles in this, his 61st year?
"A lot of low-carb stuff, lean proteins, a lot of vegetables. Every day might be a little different for him. He eats every three hours.
"What he calls his "secret weapon" is a little piece of dark chocolate. He eats one square every day," says Williamson.
