For the health of the pulmonary (breath) and circulatory (blood flow) systems, and to significantly reduce major disease risk like heart disease, stroke and diabetes, among many others, and for increasing stamina and general physical vitality. Here are the most important qualities to include in your cardio program (2-6x/week, 15-60 minutes total per workout unless you are a competitive endurance athlete):

1. Minimal impact to reduce spine and joint stress
2. Fluid, full range movements to optimally load the heart and lung output rather than overwork the muscles
3. Full-body recruitment to disperse joint load and maintain balanced muscle endurance development and joint mobility
4. If you have established a health/fitness base to accommodate it, short, high-intensity cardio bouts of a few to several minutes are better than long, lower intensity bouts.

Of course exercises that include mostly upper body or mostly lower body movement, some impact and joint stress can be very effective at raising your heart rate and aerobic capacity (racket sports, running, basketball), there is a cost to the wear and tear on the joints and they are not as efficient as multi-plane, low-impact full body movements of a similar intensity. A typical cardio circuit I run with a client is two minutes on the elliptical trainer, one minute slamming and catching a medicine ball off the bounce, and another two minutes power walking with a harness while I hold him/her back via a heavy resistance band. That’s five minutes, which I might do four times in an hour. Even if you’re in great shape, that’s plenty.