By Jailene Cuevas Kim Kardashian is the definition of a muscle mami in a new workout video posted on social media. The SKIMS founder has been posting videos of her workout routine on Thursday. Kim was showing off her back muscles while wearing an all black Lululemon workout set and doing sets of a type of row with a 20lb (9.07 kilogram) weighted bar. It seemed that she was joining her sister, Khloe Kardashian’s, workout. She captioned: “Workouts w @khloekardashian really do it for me.” Khloe asks Kim what was she training for and Kim replied, “life.” She continued to post workout videos on her…