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PostPosted: Mon Mar 09, 2015 1:12 am 
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What is the best forum on the Internet for hardcore exercise physiology questions?

One question I have is regarding how to interpret CO2 to O2 ratios in VO2Max testing. My understanding is that aerobic metabolism that uses 100% fat will give CO2 to O2 around 70%. Aerobic metabolism that uses 100% glucose will give a 1:1 ratio. And of course when you hit VO2Max the body cannot use more O2 to produce energy and there is a surge of CO2 as glycolysis takes over as the means of producing more energy.

My question is can we deduce anything about how your body is using fat and glucose for fuel when we get the CO2 to O2 ratio while you are at rest? Or do these ratios only apply during exercise under a workload?


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PostPosted: Mon Mar 09, 2015 1:04 pm 
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If you find a resource let us know. The only time I've every seen this discussed is when Peter Atia wrote about his ketosis experiments. http://eatingacademy.com/how-a-low-carb ... erformance

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Let thy food be thy medicine, and thy medicine be thy food.~Hippocrates
Strength is the adaptation that leads to all other adaptations that you really care about - Charles Staley
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Thanks TimD


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PostPosted: Tue Mar 31, 2015 9:33 pm 
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What you are referring to in your question is the RER (respiratory exchange ratio). The equation is R=VCO2/VO2. That is the ratio of carbon dioxide produced to the oxygen consumed, you were correct that with 100% utilization of fats it will produce a number of .7 that is due to the chemical equation of fat oxidation which is C16H32O2+2302---->16CO2+16H20 when reduced is equal to 16CO2/23O2 =.7

But as for the second part of your question whether we can conclude information on fat/carbohydrate utilization at rest and the answer is yes. As long as the subject is at steady state which is an unchanging level of some physiological variable, which is met within 1-4 minutes depending on untrained/trained.

Hope this helped!!


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PostPosted: Wed Apr 01, 2015 12:19 am 
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jkalasardo wrote:
What you are referring to in your question is the RER (respiratory exchange ratio). The equation is R=VCO2/VO2. That is the ratio of carbon dioxide produced to the oxygen consumed, you were correct that with 100% utilization of fats it will produce a number of .7 that is due to the chemical equation of fat oxidation which is C16H32O2+2302---->16CO2+16H20 when reduced is equal to 16CO2/23O2 =.7

But as for the second part of your question whether we can conclude information on fat/carbohydrate utilization at rest and the answer is yes. As long as the subject is at steady state which is an unchanging level of some physiological variable, which is met within 1-4 minutes depending on untrained/trained.

Hope this helped!!


Thanks for that information. So I guess it would be important not to hyperventilate at the start of a VO2Max test. It will throw off the VCO2/VO2 ratio and you might lose a view into your fat burning ability at rest.


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