"Cardio sessions deplete liver glycogen. Weightlifting uses muscle glycogen. The corresponding sugars that replenish these stores, fructose and glucose, interfere with the absorbtion of one another, which is significant in the critical span of time you would want to take opportunity of post-lifting to drink your protein shake.

A few minutes of moderate cardio as either a warm-up or a cool-down prior to, or after, lifting is fine, however. That can increase growth hormone secretion. "