The 23-year-old took to Instagram on Friday to share a selfie of him and his famous father pumping iron. Joseph joked that he would "be hurting tomorrow" after having one of the toughest trainers.
"This selfie was taken moments before my dad suggested I do 'forced reps' for the rest of the workout. You have to go all out and absolutely NO cheating when you train with him, so you know I’m going to be hurting tomorrow," Joseph wrote. "Overloading on the rows, bench press, pull downs, etc... thankfully my studly training partner helped me get every last rep. This is another great approach to training and a fantastic way to build size and strength! Try it out with your training partner 💪."
Joseph is the child of Arnold and his former housekeeper, Mildred Baena. It was revealed in 2011 that he was his son. The Terminator star also has four children -- Patrick, Katherine, Christina and Christopher -- with his ex-wife, Maria Shriver.
Just last month, Patrick and Joseph enjoyed a rare outing together. The two, along with Joseph's girlfriend, Nicky Dodaj, were photographed on a hike. The half-siblings have not been spotted out publicly before.