Christian Bale's performance in 2004's The Machinist is startling not just because of the intensity the actor brings to the role, but also the drastic weight loss he underwent as part of the performance.

It was certainly a bold move, and helped cement Bale's reputation as a seriously committed actor. But did he push himself even further than necessary based on a few lines in the film's script that were never intended for him?

During a Reddit AMA, Bale's co-star Michael Ironside describes that when the writer wrote the script, "he was 5 foot six and he put his own weights in, so he used his own weights for somebody who would be losing weight. So Chris made the weight of either 137 or 127 - so he said 'Don't change the weights in the script, I want to see if I can make them.'

"The weights he puts on the wall [in the film], that is his ACTUAL weight," Ironside explains. "He wanted to make the weights that the original writer put in, in relation to himself. And Christian is 6 foot, 2 inches. And he did."

Luckily - given how unhealthy such dramatic weight loss was proving - Bale started bulking up again very quickly. Ironside recalls that "Christian had made the weights in the script, and from that day forward - that was the day they were filming the most emaciated scene - he slowly started putting his weight on. When I saw him again at Sundance 6 months later, he had put on almost 60 pounds of muscle to get ready for Batman."

Definitely a case of 'don't try this at home'.

You can read the full AMA and more stories from Michael Ironside's long career here.