PeopleImages // Getty Images 6 min read YOUR BODY HAS over 600 muscles, and they’re all working together to help you move and live your best life. Determining exactly which of those muscles to focus your time and effort on in the gym is a bit more of a challenge. Fitness pros tend to organize all of these into different muscle groups (think upper body, lower body, core, and legs). If you don’t have a specific goal in the gym—and sometimes, even when you do!—it can feel daunting to determine how to structure your exercise. That's why veteran gym goers incorporate something called a workout split (or sometimes, a training split ) to best address all these muscle groups and strategize which you should address in your individual workouts. "Instead of training everything on one day, we are splitting up what we train onto different days," Ebenezer Samuel, C.S.C.S. , MH fitness director, says.…