science question - how could calories burned during exercise be accurately measured?

[Special K]

A friend of mine recently picked up a heart rate monitor/calorie counter and insisted that it was actually measuring calories burned throughout the day. Without knowing anything about the product, I said it was probably just using the inputted information (age, height, weight, sex) along with the measured heart rate and some internal data tables to come up with an estimate for calories burned that may or may not be accurate. How accurate could they be if you wear them 24/7?

This had me thinking - would it be possible to measure the actual number of calories burned during exercise? I assume the person would have to workout in some sort of lab or sealed chamber, but is it even possible to make this measurement accurately? If so, how exactly would it be done?

I tried searching google but all of the results are just equations and calculators that give an estimate.

 

[SociallyChallenged]

Yes, you can do it through direct calorimetry or indirect calorimetry. Direct calorimetry involves being put in a room that measures your heat output. It's rather intense and expensive so it's rarely used. Indirect calorimetry utilizes the exhaled breath of people, specifically measuring CO2 to infer information about calories burned. This is the most common way to measure calories burned, especially in exercise tests.

 

[Megatomic]

Indirect calorimetry utilizes the exhaled breath of people, specifically measuring CO2 to infer information about calories burned. This is the most common way to measure calories burned, especially in exercise tests.

This is how the elite ironman triathletes do it, along with VO2 max and windtunnel testing for power output. I'd like to know this info myself, but I can't even fathom the cost.

 

[Special K]

Yes, you can do it through direct calorimetry or indirect calorimetry. Direct calorimetry involves being put in a room that measures your heat output. It's rather intense and expensive so it's rarely used. Indirect calorimetry utilizes the exhaled breath of people, specifically measuring CO2 to infer information about calories burned. This is the most common way to measure calories burned, especially in exercise tests.

How does knowing amount of CO2 exhaled tell you how many calories were burned?

 

[SociallyChallenged]

How does knowing amount of CO2 exhaled tell you how many calories were burned?

Almost all CO2 that you exhale is the result of metabolism. You digest a fuel (carbs, protein, fats) and convert it to CO2 and H2O, while utilizing the bonds' energy in the process. Since they can measure the concentration of CO2 in the patient's expired air and compare it to the amount of O2 he/she is consuming, they can determine what macronutrient is dominantly being digested. Each macro has what's called a respiratory quotient (carbs - 1.0, protein - 0.85-0.90, fats - 0.7). These are the proportions of CO2 exhaled to O2 inhaled. With this proportion, they can measure the total liters of CO2 exhaled, use the respiratory quotient to specify which macro is dominant (or calculate how much is of each), and calculate the caloric usage. Metabolism is all in the breath 🙂

 

[Special K]

Almost all CO2 that you exhale is the result of metabolism. You digest a fuel (carbs, protein, fats) and convert it to CO2 and H2O, while utilizing the bonds' energy in the process.

When you say "digested", don't you really mean "burned"? What if I eat something and don't do any activity for awhile? Won't the food be stored as fat, and then the fat will be broken down later when the energy is required?

Since they can measure the concentration of CO2 in the patient's expired air and compare it to the amount of O2 he/she is consuming, they can determine what macronutrient is dominantly being digested. Each macro has what's called a respiratory quotient (carbs - 1.0, protein - 0.85-0.90, fats - 0.7). These are the proportions of CO2 exhaled to O2 inhaled. With this proportion, they can measure the total liters of CO2 exhaled, use the respiratory quotient to specify which macro is dominant (or calculate how much is of each), and calculate the caloric usage. Metabolism is all in the breath 🙂

Same question as above - When you say "digested", don't you really mean "burned"?

 

[SociallyChallenged]

When you say "digested", don't you really mean "burned"? What if I eat something and don't do any activity for awhile? Won't the food be stored as fat, and then the fat will be broken down later when the energy is required?



Same question as above - When you say "digested", don't you really mean "burned"?

Yes, yes I do. I was taking into account that people frequently have meals in their stomachs when they do tests like these. I was just using synonyms, but you're right. Burned or metabolized would be better word choice.

 

[Special K]

Yes, yes I do. I was taking into account that people frequently have meals in their stomachs when they do tests like these. I was just using synonyms, but you're right. Burned or metabolized would be better word choice.

Is it possible to quantify the amount of energy used to produce muscular hypertrophy?

 

[SociallyChallenged]

Is it possible to quantify the amount of energy used to produce muscular hypertrophy?

What? No. It's variable depending on the individual's mass, energy state, hormonal state, hormonal sensitivity, blah blah blah. The amount of energy put into hypertrophy differs greatly due to genetic differences. You can't account for ALL of these differences and try to quantify hypertrophy. It doesn't work that way.