Quote (Honestly @ Aug 4 2010 10:24pm)
why do they call it cardio training? is it your heart muscle that is burning the most calories?
cardio does in fast work the heart muscle quite a bit...however the actual contraction of the muscle with every beat is most certainly not the reason for caloric burn. When performing cardio, all of the body's functions are being used and heavily stressed, INCLUDING: heartbeat, respiration, blood flow, various muscle contractions (legs/torso/etc), metabolism (krebs cycle or ketosis), etc.
In essence, aerobic activity works almost every part of your body when performed properly. On a chemical level, your body detects the need for fuel in order to satisfy its energy requitements during such strenuous prolonged activity. This is where the body starts to release energy from oxygen and carbon dioxide....produced through glycogen....and eventually fat. If you are already in ketosis, then the glycogen stage is completely bypassed and fat burn is direct.
I'm getting off topic here....was your original question even legitimate? if so, I think I answered it...but it's late and I'm very tired lol