given VCO2 and VO2 what’s the formula to calculate CHO usage in grams pet minute?
I thought this was about the side effects of some gels…
Given VCO2 and VO2 you can calculate RER (respiratory exchange ratio), VCO2/VO2
An RER of 0.70 indicates that fat is the predominant fuel source, RER of 0.85 indicates a mix of 50/50 between fat and carbohydrates, and any value above 1.00 is indicative of carbohydrate being the predominant fuel source.
To get g/min from that… I do not know. I don’t have an ex phys book in front of me; I Wikipedia’ed.
Man, I thought this was going to be a thread along the lines of…
Whenever I do a long swim, I get really bloated and gassy.
given VCO2 and VO2 what’s the formula to calculate CHO usage in grams pet minute?
Since one’s starting assumptions can differ slightly, there are actually multiple formulae out there. However, Frayn gives it as:
Carbohydrate oxidation (in g/min) = 4.55 x VCO2 (in L/min) - 3.21 x VO2 (in L/min) - 2.87 x urinary nitrogen excretion rate (in g/min)
Actually tigerchik is on the right track. But you need to combine the RER with your VO2 in order to estimate your CHO usage/min.
You burn about 5 kcal for each liter of O2 consumed, so take your VO2 in L/min and multiply by 5. This will give you how many calories per minute you are using.
Then figure out what percentage of the calories are coming from CHO (from tigerchik’s post). Multiply that percentage with how many calories per minute you are using. Since CHO’s provide 4 kcal/gram, divide the number of calories per minute by 4. That will give you an estimate of how many grams of CHO per minute you are using.
Actually tigerchik is on the right track
Andrew Coggan’s post trumps mine. I’m just an undergrad, he has his degree!
Actually tigerchik is on the right track
Andrew Coggan’s post trumps mine. I’m just an undergrad, he has his degree!
I’m an undergrad too. That’s why his formula is really fancy and most likely has research to back it up. Mine is just me trying to remember what I learned last semester in exercise physiology.
given VCO2 and VO2 what’s the formula to calculate CHO usage in grams pet minute?
Since one’s starting assumptions can differ slightly, there are actually multiple formulae out there. However, Frayn gives it as:
Carbohydrate oxidation (in g/min) = 4.55 x VCO2 (in L/min) - 3.21 x VO2 (in L/min) - 2.87 x urinary nitrogen excretion rate (in g/min)
Thanks Andrew - thats sort of what I am looking for. Unfortunately I don;t have the “urinary nitrogen excretion rate”. Is there any way to work it out when limited to the following data - VCO2, VO2, R, Ve
Cheers.
given VCO2 and VO2 what’s the formula to calculate CHO usage in grams pet minute?
Since one’s starting assumptions can differ slightly, there are actually multiple formulae out there. However, Frayn gives it as:
Carbohydrate oxidation (in g/min) = 4.55 x VCO2 (in L/min) - 3.21 x VO2 (in L/min) - 2.87 x urinary nitrogen excretion rate (in g/min)
Thanks Andrew - thats sort of what I am looking for. Unfortunately I don;t have the “urinary nitrogen excretion rate”. Is there any way to work it out when limited to the following data - VCO2, VO2, R, Ve
Cheers.
You could use one of the tables out there that are based on assuming a non-protein RQ. Alternatively, you would either ignore the last part of the equation that I posted, and/or assume a constant rate of urinary nitrogen excretion (e.g., ~0.01 g/min). Either way will result in minimal error, at least under most exercise conditions.
I have a vague notion of what you guys are discussing here but I’d like to see it explained in layman’s terms if possible.
given VCO2 and VO2 what’s the formula to calculate CHO usage in grams pet minute?
Since one’s starting assumptions can differ slightly, there are actually multiple formulae out there. However, Frayn gives it as:
Carbohydrate oxidation (in g/min) = 4.55 x VCO2 (in L/min) - 3.21 x VO2 (in L/min) - 2.87 x urinary nitrogen excretion rate (in g/min)
Thanks Andrew - thats sort of what I am looking for. Unfortunately I don;t have the “urinary nitrogen excretion rate”. Is there any way to work it out when limited to the following data - VCO2, VO2, R, Ve
Cheers.
You can estimate this based on taste. If it’s bitter there is a higher concentration of nitrogen. I can steer you to a website that has a table of flavor descriptions vs nitrogen concentration.
Hey Tom -
So basically what the discussion is about is at what Respiratory Exchange Ratio- RER - the ratio of CO2 produced VS the amount of O2 consumed) during physcial activity.
This can be determined by analysing Gas Exchange in a lab during say a VO2max test. A bunch of pretty high tec equipment is required to get all of these values (VCO2 and VO2 and RER etc).
It must be kept in mind that to use RER to estimate the substrate utilization (energy source used - Carbs or Fats), one needs to have reached a steady state of activity.
When we see a RER of 0.7, almost (if not) all of the bodies energy requirments are being met by Fats (through Lipolysis).
As the intensity increases, the RER too increases, and say we get a reading of 0.85 - the energy requirements are met by 50% Fats (Lipolysis) and 50% Carbohydrates (Glycolysis).
Maximal effort see the RER approach 1.0, where Carbohydrates (trough Glycolysis) are 100% used for energy requirements.
The reason Fat can only be utilized at lower intensities is that in order for Fat to be metabolized, it requires a highly O2 rich enviroment VS Carbohydrates (Carbs have contain more O2 than Fats).
Also keep in mind that seldom will you be at 100% Lipolysis or 100% Glycolysis - more often than not, the body gets a contribution from different pathyways to meet its requirements.
Hope this helps
Maximal effort see the RER approach 1.0, where Carbohydrates (trough Glycolysis) are 100% used for energy requirements.
No, maximal effort is actually closer to 1.1, 1.2, and I’ve even seen a few slightly higher. 1.0 is closer to VT
You can estimate this based on taste. If it’s bitter there is a higher concentration of nitrogen. I can steer you to a website that has a table of flavor descriptions vs nitrogen concentration.
Classic.
“If it tastes like wheat grass you need to adjust your training to be less…”
-Jot
Good Lord, the man just wants CHO oxidation rate in g/min!!! Plain and simple way, without the need for wee-wee (ie, assumes non-protein, which likely is easily close enough for this application…):
Carbohydrate oxidation rate (g/min) = 4.585 x VCO2 – 3.226 x VO2