RE: Heart Rate & Low Intensity Cardio Question.
Well low intensity is a very broad term.
Cardio vascular intensity is generally guaged by how it effects the heart rate.
For example, if you were walking and your heart rate was at 100 BPM, this would constitute approx 55% of your Maximum Heart Rate which is widely accepted as low intensity.
If you broke out into a run and your heart rate raised up to 170 bpm, this would be approx 85% of your MHR thus being high intensity cardio work.
It is generaly accepted that low intensity activity in the morning on low glycogen (thus low insulin) burns fat well.
It is also accepted that high intensity inteval training (HIIT) also burns fat well due to the EPOC (excess postworkout oxygen consumption due to raised body temp for the rest of the day)
What you choose depends on your lifestlyle. Training for sports performance is another kettle of fish altogether.