See pic: JK Simmons is getting pumped for 'Justice League'!

Actor JK Simmons is putting on muscles in preparation for his upcoming turn as the police chief of Gotham in Justice League.

Aaron Williamson, a former Marine and competitive bodybuilder who becomes Simmons' personal trainer, revealed the actor's transformation in a photo he posted on Instagram on June 3.

In the photo, Simmons can be seen working out in a gym. Lifting weights and using an arm-blaster, he showed off his impressive physique.

"Every time we train together I forget he's 61 years old. So much respect for this guy," Williamson captioned the picture, adding the hashtags #JKSimmons and #OldmanCranking.

 

A photo posted by Aaron Williamson (@aaronvwilliamson) on Jun 2, 2016 at 8:52pm PDT

 

A photo posted by Aaron Williamson (@aaronvwilliamson) on Apr 30, 2016 at 10:15am PDT

The bodybuilder trainer, who is also a personal trainer to Dwayne "The Rock" Johnson and James Marsden, explained that the Dark Skies actor's training motivation was to keep himself healthy.

"His goal was to have 'sick arms,' " the trainer explained . Later, Simmons started to fall in love with fitness.