Cardio is cardio because of your engagement of large muscle groups... the reason we use heart rate to measure it is because we understand the mathematical relationship between exercise and heart rate and calorie burn. It's not the heart beating that causes the actual calorie burn, because the heart is actually a very tiny muscle in relation to the others.
That's why sitting in a sauna, watching a scary movie, and getting a tattoo get your heart rate up, but don't necessarily burn more calories... because you aren't engaging the muscles that actually do the burning. For this reason, people who have heart conditions that cause artificially high heart rates have a hard time using heart rate monitors because they get inflated calorie counts. Your heart working harder doesn't translate to more calorie burn, I'm afraid.
Writer, mother, wife, and breadwinner. I love to run, but running doesn't love me, so I'm switching to my low-impact bike.
I'm not pregnant, just fat: My blog. fatnotpregnant.blogspot.com/
| current weight: 190.6