it's easy to isolate the arm muscles when using free weights or cables.Simply grab a weighted implement and flex or extend the elbows. Things become more complicated,however,when trying to use your body as a barbell.It's difficult to manipulate the body around the elbow joints.This isn't to say that it's not a good idea to try to target the arms with single-joint movements. But it is critical to understand that multi joint movements are the most productive in terms of total muscular output.