I think Awex is confusing heart rate and calorie expenditure - they aren't actually directly correlated in any way.
As the original poster seemed to have a calorie-burn-bias:
- It doesn't matter how much you rest. If you run for 10mph for 30minutes or run at 10mph for 10min x3 with rests in between, it's still the same calorie expenditure.
The breaks do lessen your heart rate, thus your cardiovascular workout. Which still isn't the end of the world. To be honest, I would not overly concern yourself with heartrate or beats per minute, but more with progression in speed, distance or duration from week to week.
Not confusing them at all, the best measure of calorie expenditure is heart rate, unless of course you've got a lab handy. For example if your walking you'll have a low heart rate, if your running flat out you'll have a very high heart rate, running flat out is harder therefore burns more calories and therefore a higher heart rate means more caloires burnt. Obviously it's not directly correlated as people get elevated heart rates for all manner of reasons such as being scared, nervous etc. but generally speaking in cardio the higher your heart rate the harder intensity your cardio is and therefore the more caloires burnt.
Now I did say that breaks don't effect the calories burnt much at all, all I said was that 20 minutes is generally the time people have to exercise for before starting to burn fat, and that resting is bad for the muscles, including the heart. Not bad as in it'll harm your heart, bad as in it won't improve your stamina as much. The longer you push your cardio vascular system i.e. raise the heart rate, the more efficient it becomes at it's job (pumping oxygenated blood round the body to the working muscles) which in turn means your heart will pump more blood each beat which in turn reduces your heart rate, if you stop every few minutes before your heart rate gets higher, your not pushing your cardiovascular system as much and therefore not improving it's efficiency. The more efficient you CV system is the harder and longer you can work as a result. Increased intensity and duration leads to increased energy expenditure as a result, so I would say not having breaks is important to anyone trying to lose weight.
And if your heart rate doesn't increase when your start exercising you've got problems, therefore in summary there is correlation between heart rate and calories burnt, it's not an exact science by any means but it's the best indication without sophisticated technology as too how many calories your burning.
But saying all that, I personally don't watch my heart rate as I know my body well enough to know when I'm not working hard enough and when I am. But for the beginners who don't know their limit looking at heart rates gives a good general indicator.
Most of what I just said is regurgitated from a number of text books, but hopefully I simplified it enough for it to make sense without losing the essence of what I was gettign at. And in order to save our sanity I will stop there before I write an essay about prolonged exercise and it's effects on the muscles and the difference between aerobic and anaerobic systems and the energy expenditure experienced as a result of each

but i can if someone really wants
