The relationship between heart rate and calories burned?

Calories burned are measured indirectly as a function of oxygen consumption. Heart rate is an indicator of oxygen consumption in that when you need more oxygen to your muscles and other cells, your heartrate goes up to deliver that oxygen where it needs to be. If the caloric need is high (ie you're burning lots of calories to perform the required task) then oxygen demand is high. If oxygen demand is high, then heartrate goes up. Since you can't measure your oxygen consumption or caloric need directly, you can measure your heart rate and get a decently accurate idea of what's going on. And there's no two ways about it, the most accurate way to actually accomplish this is with a heart rate monitor. Cardio machines that give you calories burned only use an algorithm based on broad range average estimates in the general population. Odds are excellent they are wildly inaccurate.

For the first time in my life I am exercising every day of the week. I aim for at least 30-45 minutes of something- elliptical, swimming laps, horseback riding, or walking the dogs. And it's going great!

But I am seriously confused about the relationship between heart rate and calories burned... and how to get the most accurate calories burned count for my work out.

It seems to me that every work out there are lots of variables. For example, today on the elliptical I could give you all of this information:

45 minutes, HR avg 140, 3.55 miles, resistance level 5, incline 5.
The machine says I burned 390 calories, mapmyfitness (where I log my workouts) says 408, and this calculator* says 359 calories. (This example just has a calorie difference of 50 calories, but when it's swimming or zumba or yoga it gets loads more confusing.)

The elliptical machines and perhaps other devices as well are reportedly set for the average 180 pound male. I have heard this from more than one fitness club. Since you are clearly not a 180 lb guy, if you want a more accurate cal count on a number of different exercises, you will, alas, need a HRM. Personally, I don't want another device in my life at the moment. Have enough high maintenance toys will little screens that I need my kids to explain how to use. In the winging it category, I just cut back the MFP exercise calorie numbers that always seem high by some amount that suits me that day depending on how I hard I figure I worked, and that's been good enough to stay out of the obsessive compulsive help group websites. I respect those who must need to know exactly, however I am just not yet willing to cross over to that level of counting.

Wow, I'm so glad to have found this topic! Thanks to all that contributed. I just ordered the Polar FT4, I think it comes with a chest strap. I am also using the fitbit to help calculate what I'm burning through the day. But I usually take the fitbit off when I'm doing something like Turbo Fire, and then just try to use an exercise from the data base. That's why I'm excited about the FT4...I'm hoping to be able to enter the calories burned doing other activities besides walking and stairs. Thanks again!!

If oxygen demand is high, then heartrate goes up. Since you can't measure your oxygen consumption or caloric need directly, you can measure your heart rate and get a decently accurate idea of what's going on. And there's no two ways about it, the most accurate way to actually accomplish this is with a heart rate monitor.

Unless the HRM contains the data to measure an individuals current fitness level then the calorie counts are basically wild guesses.

Two individuals of equal weight may be exercising, one with a heartrate of 130 and the other with a heartrate of 160. Is one working harder or is he just out of shape? If they are both doing the same exercise at the same workload the calorie burn ought to be the same, no matter what their heartrate is.

A person who is aerobically fit will have a heart with a much larger stroke volume than a person not fit. That means that his heart does not have to beat as fast as the other person's to supply the exact same oxygen demand.

People who think that their calorie counts go down as they get in shape and their heartrates drop are wrong. Normalizing for weight the calorie count stays the same for equal workload. If the HRM says the calorie count is down then that should be an indication that the HRM calorie count is wrong.

The truth is that as a person becomes aerobically fit they ought to be able to produce increasing calorie burns in equal time because they will be able to exercise at increasing levels of workload at the same exercise intensity without an increase in heartrate.

If the HRM is not reflecting this then the HRM is simply wrong.