There is a big belief that doing some cardio activity (aerobic steady state) would hinder any efforts made earlier through resistance training due to different hormones secreted during each.

A new study shows that in moderation, aerobic training can actually enhance muscle building pathways and lead to greater adaptations.

The mechanism behind this process still remains unknown and it will be interesting to follow more research into the subject as it will published in the next few years.

Read the paper here