The former professional bodybuilder has been moonlighting in a California gym as instructor "Howard Kleiner"
Would you work out harder if you knew Arnold Schwarzenegger was your coach?
The Hollywood movie star and former governor of California, has gone undercover at Gold's Gym in Venice, California, wearing a black wig and moustache.
Disguised as Howard Kleiner, a "fitness instructor who had become regional manager for Gold's Gym", Schwarzenegger was filmed approaching clients mid-workout to give them tips on their training.
Standing over one member doing sit-ups, the star of Terminator tells her: "you have elbows and knees, so touch them."
He then encourages another member to include "ten reps of water sipping" between each set of exercises.
Schwarzenegger's appearance was a stunt to promote and raise funds for After-School All-Stars, a nationwide programme that provides free mentoring, homework help, tutoring and fun activities to students from low-income families.