Mark Wahlberg: Biceps & Blood on 'Pain & Gain Set'!

Mark Wahlberg shows off his bulging biceps in a tank top splattered with blood on the set of his film Pain and Gain on Friday (May 4) in Miami, Fla.

The 40-year-old actor beefed up for his role in the upcoming Michael Bay-directed film, but he did not use steroids to achieve his look.

“Even though the film is about steroid abusing gym rats, he took it as a personal challenge to get to the size he is at now and has been training non-stop,” a source told Us Weekly.

Also pictured inside: Mark listening to music while hanging out shirtless on his hotel balcony.