jerseyjunkie

How do heart rate monitors calculate calories burned? I understand that it is related to heart rate and zones, but I am interested in seeing the actual mathematical equation. I looked at Polar's site, and didn't find anything.

Anyone know the answer, or have a link?

WD_40

Something to do with age, VO2 max and heart rate, I think. Hmm... I'm curious now. Google, here I come.

Edit: Looks like it's calculated based on body weight, gender and exercise heart rate. Haven't been able to find an exact formula yet.

DannoXYZ 

It's a guesstimate... there is no way the HRM can tell if it's measuring 175bpm on Lance's heart or yours or mine's. Take that number it gives you and add a +/-25% fudge factor. The only real way to calculate calories burnt is in an isolated thermal chamber.

jerseyjunkie

Danno, that's kind of my point. I want to see the formula, so that I can see what relation it may or may not have to other factors that would be at play.

jerseyjunkie

Also, since calories can be converted directly into watts [1 watt = 0.239 calories/second] (those are small calories, btw), then one could theoretically translate this into power.

Does anyone use separate power meters and heart rate monitors? Have you ever compared the different readings? It would be interesting to see under what circumstances the two readings are most highly correlated.

mayukawa

I doubt a bike power meter and the calories expenditure on a HRM would match up (even if they're accurate). The bike power meter just measures power onto the bike, whereas the cyclist uses power not only to power the bike, but other things like steering, breathing, etc.

I don't know what formulas they use, if they even use any formulas. It could just be some numbers based on a statistical chart based on people's weights. It could be just W=F x d=ma x d. The HRM knows your mass (m), but it does not know your acceleration (unless you're working against gravity and then it's g*sin(angle relative to perpendicular)) nor distance. But I guess there's probably a physiological approximation on how much blood ones heart pump that equates to how much approximate energy one's using (as a function of body mass). Of course the HRM doesn't quite know what kind of cardiovascular shape the person is in (though that's approximated by the peak heart rate)... Probably somebody with a human physiology background can jump in and set us straight...

scot

You would really need the isolated chamber to measure the heat produced into the atmosphere. Anything else is just guessing.

Also a beginnier going 10mph huffing, puffing and sweating like there is no tomorrow with a HR of 185 is going to be working much harder than a pro going the same speed. s/he will be consuming more calories over all because of the damage to what little muscles there are, skeletal changes, heat buildup etc. A more experienced rider's body will be more efficient at the exchange and shouldn't use as much energy to go the same speed. This is really the main thing HRM's are doing is giving a calc which is skewed towards perceived/real effort vs some formula saying it takes 500 calories to do so much work at such a speed.

Scot

F1_Fan

See my posts in this thread:
https://www.bikeforums.net/road-cycling/169469-so-who-s-got-distorted-body-image-here.html#post2098195

IMO the Polar calorie function is probably a lot more accurate for walking and hiking than cycling (coasting and soft-pedalling probably being two big sources of error).

pacemaker

When you set up the HRM it will ask for Ht Wt Age and Gender. The HRM will then use the Harris-Benedict equation to calculate your BEE ( Basel energy expenditure). It will then use your BEE to calculate the amount of kcals your are burning based on your exercise intensity relative to the Max HR you have entered. They are pretty accurate as long as the info you put in it is accurate.

zero

ya... the human body is nowhere near 100% efficient in converting calories into power. 1 Calorie(kcal) is around 4 ish kilojoules. I can easily burn around 1000 kcal in an hour but it is impossible to burn 4000 kJ in an hour (thats like 1100 watts continuous).

F1_Fan

The efficiency is widely held to be about 25%. Therefore kJ measured with a power meter is pretty damn close to calories burned while exercising since 25% of 4 is 1.

For the poster above who mentioned steering and breathing... the energy demands of that are pretty minimal compared to muscle groups like the quads when they're pumping away.