After pumping himself up to huge proportions to play a bodybuilding criminal in Pain & Gain, Mark Wahlberg had to trim himself back down to play a Navy SEAL in Lone Survivor – Peter Berg’s Afghanistan-set thriller that tells the real-life story of a group of marines who soon turn from hunters to hunted during a mission to take down a notorious Taliban leader.

Ditching the isolation machines altogether, Wahlberg hired long-time trainer and Brian Nguyen – a key member of the 42-year-old actor’s entourage since working with him on 2006’s American football drama Invincible – to prepare him for the rigourous marine bootcamp he was about to embark on. MF caught up with Nguyen to find out how he used functional training to get Wahlberg battle ready…

Mark only had four weeks in between finishing Pain & Gain and starting on Lone Survivor. We got him back down to around 185lbs [84kg] from 210lbs [95kg] by cutting out the weight training and switching his diet from eating heavy to eating clean. After all the bench pressing and heavy squatting he was doing for Pain & Gain, we also had to reestablish his shoulder and hip mobility as he was dropping weight.

As soon as he got to the Lone Survivor set in New Mexico he went straight into marine training, which involved a lot of functional work – running up and down hills with a gun and a heavy backpack – so if he didn’t have that mobility it would have been a disaster.