There are two types of anabolics:
Class-I)These are mostly the oil-based injectibles.They work primarily by binding to and activating the androgen receptor,which then interacts with your DNA,sending out various signals to impact anabolism/anti-catabolism.
Class-II)These are primarily 17alpha-alkylated oral compounds.They,unlike their oil-based counterparts,do not bind well to the androgen receptor,and acheive their effects on growth/strength independent of this process,by binding to other types of receptors.
The above study just offers some actual scientific proof into this,and sheds light on why it is beneficial at times to stack steroids from opposing groups,so as to get the maximum results through multiple pathways,as opposed to one primary mechanism...