longtrousers wrote:
ericMPro wrote:
longtrousers wrote:
DrAlexHarrison wrote:
longtrousers wrote:
These are two graphs from a performance diagnostics (spirometry): the left from a beginner, the right from a trained person.
The yellow curve is indicative for fat burning, the blue for carbohydrate burning.
Any chance you can zoom in on each graph and repost for a clearer picture and discussion?
I posted these graphs just to show my understanding that any spirometry shows that fat burning goes to null at a certain intensity. So it is not important for that to know the exact values in those graphs. These graphs show the different gasses you exhale which should be indicative to fat burning and carbohydrate burning. I'm far from being an expert and maybe eircMPro is right that you indeed always burn at least some fat, it only surprised me because I had an other understanding.
You are burning fat from the time you are born until the time you die and every nanosecond in between.
Here is another illustration of what I mean:
https://iconoclasses.com/...-maximal-effort-rer/ At the moment the respiratory quotient (RQ) = 1, there is no fat burning anymore, I quote from the beginning of that article:
"
A ratio of 0.7 is indicative of mixed fat use, whereas a ratio of 1.0 indicates the exclusive use of carbohydrates. Thus, during low- intensity, steady-state exercise, the respiratory quotient and the RER are typically between 0.80 and 0.88, when fatty acids are the primary fuel. As the intensity of the exercise increases and carbohydrates become the dominant or primary fuel, the respiratory quotient and the RER increase to between 0.9 and 1.0."
RQ's in excess of 1.0 are possible during higher intensity exercise. 1.1 and 1.15 are commonly observed during VO2max ramp tests, and occasionally as high as 1.20. This onset of acid production and the resultant increased expiration of CO2 occurs before RQ=1.0, meaning that fat oxidation is still likely at RQ=1.0.
Tissue level acid (hydrogen ions) production increases as RQ approaches 1.0, and this increased acidity causes a shift in the bicarb buffering system, resulting more CO2 being breathed off, relative to actual carb use, before RQ=1.0 in a ramp test.
Therefore, RQ=1.0 likely indicates largely carb use, acid balance via respiratory system, and some lower-level fat use.
The "RQ=1.0 = exclusive carb use" is commonly taught in undergrad ex phys, and undergrad exercise physiology textbooks often contradict themselves (as is pictured here in Powers and Howley) in their pursuit of simplicity for the newer undergrad learners. I suspect that the "RQ=1.0 = exclusively carbs" argument is an oversimplification used to teach the concept of substrate utilization to undergraduate students in exercise physiology courses.
Completely shutting off the cellular machinery for fat burning in all tissues seems implausible and improbable. Reduced, yes, at highest intensities, and to the greatest extent in lesser-trained folks. (The bar graph image is a completely untrained subject with LT β
60% of VO2max).
Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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