Your body only has so much recuperative powers so when you increase your cardio to a much higher degree the extra calories aren't really going to help you recuperate to a level you may be looking for. It's the rest your body needs to grow so don't bump the cardio up much. I'm not saying you won't gain a pound or two of muscle since fina has done some amazing things but I wouldn't do the cardio at a high intensity, that will really exhaust your recuperative powers for growth.