i do 10 min jog, followed by a 10 min HIIT routine consisting of a near sprint around 3/4 of the track and then walking the remainder, and then i close with another 10 min jog. i dont think this is too much cardio for gaining mass, i'm just worried that the continuous tearing down of leg muscle will decrease my gains, i'm not a good swimmer, wish i was, but a do have bikes available