More of my VO2Max Test Results

Here’s some more data from my VO2Max Testing (Part 1 is here). The test was done fasted at about 9AM. Part 3 follows where I look at the graphs for this data.

Respiratory Exchange Ratio (RER)

One of the things I wanted to know was how much I am fat fueled. The RER is a measure of carb vs fat fuel utilization.

My initial RER at rest was 0.73. The RER number went down as the exercise started and bottomed out at 0.59. At about 7 minutes in the number started to increase and finally peaked when I tapped out at a value of 1.09. From Wikipedia:

An RER of 0.70 indicates that fat is the predominant fuel source, RER of 0.85 suggests a mix of fat and carbohydrates, and a value of 1.00 or above is indicative of carbohydrate being the predominant fuel source.

Not sure how I got RER numbers below 0.7. Clearly I am a fat burner.  Ben Greenfield say that is indicative of burning more than 100% fat (no clue what that actually means) and the machine is not calibrated to measure that. Being at a low body fat amount probably played into my inability to go longer and deeper into fat stores.

As the exercise continued my body moved to burning carbs (which I have very few of since I would have a minimal glycogen stores and the liver can only produce so much glucose at any rate).

The high RER value of 1.09 was exceeded when I was cooling down when it reached 1.11. From Wikipedia:

Calculation of RER is commonly done in conjunction with exercise tests such as the VO2 max test and can be used as an indicator that the participants are nearing exhaustion and the limits of their cardio-respiratory system.

An RER greater than or equal to 1.15 is often used as a secondary endpoint criterion of a VO2 max test.

They stop the test at 1.15 because that’s the end of where they will take you. So I was a few seconds from that time. I felt like a wimp for stopping but I can see from the numbers I was actually very close to my physiological limit. Being low carb I have very little carbohydrate (glycogen) stores to draw from so that’s another reason for my limited performance.

They will let the systolic blood pressure go up to 250 and mine peaked at 210. Incidentally, it started high. My white coat flight or fight syndrome was in full bore for much of this. Interestingly, diastolic pressure drops during exercise (for most people) and mine did as well.

Study on RER in Low Carbers

From (Nutrition, Published Online:1 Apr 2014. Effect of a very low carbohydrate diet followed by incremental increases in carbohydrate on respiratory exchange ratio (LB444). Laura Kunces, Brittanie Volk, Daniel Freidenreich, Catherine Saenz, Maria Luz Fernandez, Carl Maresh, William Kraemer, Stephen Phinney, and Jeff Volek):

Low carbohydrate diets are associated with increases in fat oxidation, but the extent to which substrate utilization is altered as individuals reintroduce carbohydrate into the diet has not been studied under controlled conditions.

We therefore examined postabsorptive respiratory exchange ratio (RER) across a broad range of dietary carbohydrate and fat levels in adults with metabolic syndrome.

After an initial 3-wk run-in low-carbohydrate diet, 16 adults (age 55 ± 10 yr, BMI 37.9 ± 6.3 kg/m2) were fed six sequential moderately hypocaloric 3-wk diets that progressively increased carbohydrae (47, 82, 131, 179, 250, 344 g/day) with parallel decreases in fat.

Resting RER was lowest after the very low carbohydrate diet and increased in a linear manner as carbohydrate increased (0.75 ± 0.04, 0.77 ± 0.03, 0.79 ± 0.04, 0.80 ± 0.04, 0.82 ± 0.03, 0.84 ± 0.05, respectively).

These findings indicate that very low carbohydrate diets accelerate fat oxidation and that progressive increases in carbohydrate track linearly with decreased fat oxidation.

Another Low Carb Athlete’s Results

Here’s Ben Greefield‘s Vo2max test results. His number stayed above 0.70 and for some odd reason I can’t explain or understand my number dropped below 0.70. That’s not supposed to happen as far as I can tell. My RER reached a low of 0.59 during the test.


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