The 33-year-old actor, who plays pilot Raleigh Becket in Guillermo del Toro's sci-fi blockbuster, had to muster all his strength while on set as some scenes required him to use the exercise machine for hours at a time, reported Contactmusic.
"There are a bunch of sequences where I pilot the giant robots. They created what was essentially a cross-trainer for us to operate them," Hunnam said.
"It's hard enough to do that for 30 minutes at a time, but I did it 14 hours a day, for 27 days, wearing a 30 pound suit. There were moments I thought I wouldn't get through it but it was worth it in the end," he added.