Bottom line on Cardio is that it is healthy to do because it helps mae the body more durable and fit. Moreover, cardio, when done correctly, can actually serve to buil and improve muscle mass!. Yes, I am serious. How? Cardio increases the peripheral circulation, which fuels your muscle pump. Important, if the circulation is poor, the pump is poor. Recovery is also circulation dependent. As lactic acid build up, the muscle becomes warm and stretched. After that, it becomes sore as an inflammatory process sets in to repair the damage. This process intimately depends on efficient circulation, as better circulation enhances your post exertion recovery. Just look at how vascular your body is after an intense cardio workout. People need to understand if cardio is done right, it burns fat, but not counterbalancing calories taken in, which is the fallacy of standard cardio approaches. Instead the principle works by stimulating the metabolism, thereby allowing your body to burn more fat throughout the day, even when you are not at the gym.
My cardio consist of interval training - I go hard: increase my speed on the treadmill for one minute (fast walk almost a a jog) and then drop to one minutes of walking at a slower rate. I do this 5 time a week.
Hope this helps.
Strako44