HRM and calories... how can it be accurate?

mauryr

I have heard often that an HRM is the best estimator of calorie burn. How can this be so?

Aren't calories a measure of energy spent? If you (lift, run, whatever) a certain amount, you will have expended a certain amount of energy, therefore a certain amount of calories (some activities must take into account your body weight).

If you are fit or strong, your body is capable of expending more energy. One person's heart will be under less stress for a specific task, and therefore beat less frequently because their system is more efficient, and/or has more headroom than someone else who is less fit. The energy required to perform a task - as I understand it - is independent of your fitness or strength.

In other words, lifting a weight (or any task) takes the same amount of energy, regardless of who does it. It may stress one person more than another due to their strength, but the calories expended would be the same.

So, why is heart rate correlated to energy output?

jamiek89

bump!

ambercole

bump

cjnorman

This is from the Polar website but it makes sense. So your heart rate is used to determine how hard you are working.

"The amount of energy expended during exercise depends on exercise intensity and duration. The higher the intensity and the longer the duration, the greater the energy expenditure. Energy expenditure is also dependent on body weight, so that a heavier person consumes more energy than a lighter one when performing the same exercise because the mass that the person needs to move is greater. For example, persons weighing 60 kg and 100 kg expend 5 kcal and 8 kcal per minute in brisk walking, respectively. Also, the larger the muscle mass used in the exercise the greater the energy expended. Thus, very high energy expenditures can be reached in e.g. cross-country skiing and rowing. Types of exercise where the person must support his/her body weight typically expend more calories than types where the exercise equipment supports the weight."


Also explains why they aren't very good for calories burned during strength training.

littlemamajamie

I am curious too....

Skylee10

I am sure someone could quickly google this, but related this to engines, a newer engine that is well maintained might take less FUEL to do the same task that an older, not well maintained engine would take. The efficiency with which the work is completed by the machine is what I am saying. Couldnt that make a difference?

In other words, someone could make a ridiculously complex enormous machine (think of an old Rube Goldberg diagram) to move a weight off of the table, with tons of moving parts and weight of its own that must be moved. Someone else might use a simple pulley to move the same object. The object hasnt changed, but the machinery moving it has. Even correcting for weight differences, I guess I am saying if one machine runs at higher RPMs than another more efficient machine, the higher RPM machine is going to go through more fuel.

Not sure if that helps, but my 2 cents. You correctly identify the weight of the person/machinery as being a factor, but I think the other correlation related to energy use is indeed the efficiency of the machine in terms of rpm's. Think of your heart as your measure of rpm's for your body, to continue the analogy.

That might be 100 % wrong, so take it for what you paid for it.

pyroxian

I like to refer people to this blog post when this topic comes up
http://www.myfitnesspal.com/blog/Azdak/view/the-real-facts-about-hrms-and-calories-what-you-need-to-know-before-purchasing-an-hrm-or-using-one-21472

Talako

http://www.braydenwm.com/calburn.htm

It is discussed at the link above.

sixpacking

you may take a 20 lbs weight just like someone else, its gonna take take same amount of force to lift it,m but calories burn will depend on your heart stress level. its all about form, fit and function...tons of people go to the gym lift improperly and because they don't maximize, they're not gonna burn like Joe or Mary, who know exactly how to maximaze.

sunshine79

Because how much energy is required to lift for example a 20kg dumbell depends on the person's level of fitness/strength.

For example, a body builder who weight trains regularly would find it pretty easy to lift that weight because his/her muscles are stronger so there would be less stress on their muscle and less energy required where as someone like me who isn't a seasoned body builder would have to put a lot of stress on my muscles to lift the same weight thus expending more energy.

nab22

HRM's use formulas to calculate your approximate oxygen consumption given your heart rate, age, gender, and weight (the less accurate ones may not ask for all these inputs). Then, that estimate of how much oxygen you used lets the HRM compute how many kcals worth of energy were combusted with this oxygen.

So, there are still more formulas going into the number on your HRM just like if you type in your height, weight, time spent on activity, gender, etc., someone online or into MFP, but the one additional piece of information your HRM has to give you an accurate calorie count is... your heart rate, which MFP doesn't know.

nab22

*somewhere online, not someone online

wmjrigo

"In other words, lifting a weight (or any task) takes the same amount of energy, regardless of who does it. It may stress one person more than another due to their strength, but the calories expended would be the same."

From what I understand...Let's say the weight is 50 lbs and the reps 10. Well someone who is not as strong is going to spend more energy trying to perform the task than someone who is stronger. Therefore the first person is burning more calories, also their heart rate will be higher.

CuteMommy88

When you are doing physical activity, your heart rate increases in order to increase the blood flow to the used muscles, this happens so your muscles will be oxygenated, the harder your muscles are working, the more oxygen they need, thus the more your heart will pump in order to supply those muscles with the oxygen they need. The reason physically fit people tend to burn less calories is because of hypertrophy which is just a slight enlargement of the heart so their HR during exercise isnt a whole lot higher than their resting HR. Im not sure if this helps any....

mauryr

I read the links posted above, and they all have good info. From a physics standpoint, the work done ON the weight (or elliptical, or whatever) is independent of who or what does it... but Skylee10's engine analogy seems to be what all of the links say, but that engine analogy seems to be a more intuitive paraphrasing..

The output energy produced by the person is not equivalent to the energy contained in the fuel consumed by the person to create that output energy. If the person's system is inefficient (like a lousy, gunky engine) it takes more fuel to produce the same output energy (like fewer miles per gallon from an inefficient engine).

So, the HRM infers the amount of energy consumed, not the output energy produced.

Collectively, we are pretty freaking smart.

Thanks, all!