Help interpreting Respiratory Exchange Ratio

Herzog wrote:

I was fortunate enough to have some lab testing done recently and I’m trying to work out what it all means, specifically the use of fat and carbs as fuel.

I’ve attached the links from the tests below for anyone interested enough to analyse. The test order was 1) 10 min warm up @100W then Sub Max test, 2) 10 min @ 100W then Vo2 max, and 3) 2h rest and then Time to exhaustion after 10min @100W.

Sub Max https://drive.google.com/open?id=1LbLlNil-rErAfs3gPIeQEWaFrs2dahM3
VO2 Max https://drive.google.com/open?id=1ICAEH8tAK1LV38UXk8FQVtu9wbTVgRGG
TTE https://drive.google.com/open?id=1Kyvt02Jo1ZNDRPeyFRw00LSuUWgGABk3


Regarding the fat/carb source utilization, I have a few questions:

1) looking at test 1 (sub max), I burn primarily carbs, even at low intensities. Correct?

2) However, test 2 (VO2 Max) relies mainly on fats…is this because the carbs have been exhausted after the sub max test?

3)TTE relies on fat at low W, but then once load is applied at 470W, carb use dominates (this is what I expected to see across all test fat>carb).

I train primarily in the mornings around 6am in a fasted state (i.e., nothing from 7pm previous evening and can complete all types of workouts like this, e.g., anaerobic/VO2 max etc with no problems) and was surprised by the sub max test. Does this really mean that I primarily rely on carbs as a fuel source until they’re exhausted, after which I switch to fats? If so, how was I able to reach VO2 max in the 2nd test, despite pulling the fuel from fat (which is far slower chemical reaction).

I find it very hard to lose weight despite a lot of training and any insights into my results would be appreciated!!

It depends a lot on your Cadence at the given power. The key to the fuelling is which muscles are engaged, at what intensity, frequency of ‘switching’ and intensity of engagement. Studies have been done which seem to indicate that a lower Cadence at a given power will burn Glycogen primarily, and the higher Cadence at that power will push the body to primarily fat burning. The degree, frequency and intensity of the fast twitch muscles engagement seems to be what differentiates between the feeding mechanisms. So Glycogen is used primarily during slow high force pedalling, and fat primarily used during fast high force pedalling. The experiment was conducted by scientists at the University of Wisconsin and the University of Wyoming, and involved asking eight experienced cyclists to cycle at an intensity of 85 percent V02max for 30 minutes under two different conditions.
In one case the cyclists pedaled their bikes at 50 revolutions per minute (rpm) while using a high gear. In the second case, the athletes pedaled in a low gear at 100 rpm. The athletes were traveling at identical speeds in the two instances, so their leg-muscle contractions were quite forceful at 50 rpm and moderate—but more frequent—at 100 rpm.

As it turned out, the athletes' oxygen consumption rates were nearly identical in the two cases, and heart and breathing rates, total rate of power production, and blood lactate levels were also similar.

However, athletes broke down the carbohydrate in their muscles at a greater rate when the 50 rpm strategy was used, while the 100 rpm cadence produced a greater reliance on fat.

Herzog wrote:

Thanks all.

Cadence was a steady 90rpm throughout - little deviation.

Regarding weight loss, it does happen, but very slowly - I'm aware of it and track calories etc.

I'm interested in thoughts relating to how the RER changes between and within tests. For example, my hypothesis that on the fuel burning continuum (I know it's not binary), I'm skewed towards burning carbs (even at lower intensities) as observed in the sub max test. But then the VO2 Max RER is confusing as the fuel was primarily fat. Could I really have burned through all stored glycogen within the 1st test? Why the switch to fat for the same intensities during the VO2 max test?

Thoughts on those aspects of the test would be welcome.

Continuing with the experiment carried out by experts, using experienced cyclists I mentioned earlier.
The greater glycogen depletion at 50 rpm occurred only in fast-twitch muscle cells. Slow-twitch muscle cells lost comparable amounts of their glycogen at 50 and 100 rpm, but fast-twitch cells lost almost 50 percent of their glycogen at 50 rpm and only 33 percent at 100 rpm, even though the exercise bouts lasted for 30 minutes in each case.

This rapid loss of carbohydrate in the fast-twitch cells during slow, high-force pedaling probably explains why slow pedaling is less efficient than faster cadences of 80 to 85 rpm.
What these experts determined with their robust scientific experiment was,
Basically, as the fast fibers quickly deplete their glycogen during slow, high-strength pedaling, their contractions become less forceful, so more muscle cells must be activated to maintain a particular speed. This activation of a larger number of muscle cells then leads to higher oxygen consumption rates and reduced economy. This scenario, in which slow pedaling pulls the glycogen out of fast-twitch muscle cells, may sound paradoxical but it isn't; after all, slow pedaling rates are linked with high gears and elevated muscle forces, while fast cadences are associated with low gears and easy muscle contractions.

Since fast-twitch fibers are more powerful than slow-twitch cells, the fast-twitch fibers swing into action at slow cadences, when high muscular forces are needed to move the bicycle along rapidly.

On the other hand, "fast" pedaling rates of 80 to 100 rpm are not too hot for the slow-twitch cells to handle. Slow-twitch cells can contract 80 to 100 times per minute and can easily cope with the forces required to pedal in low gear.

Another possible paradox in the Wisconsin/Wyoming research was that fast pedaling led to greater fat oxidation, even though maximal fat burning is usually linked with slow-paced efforts.

Basically, the higher fat degradation at 100 rpm occurred because the slow-twitch cells handled the fast-paced, low-force contractions. Slow-twitch fibers are much better fat-burners than their fast-twitch neighbors.

Fortunately, there's a bottom line to all this: During training and competition, cyclists should attempt to use fast pedaling rates of 80 to 85 rpm, both on the flat and on inclines.

Compared to slower cadences, the higher pedaling speeds are more economical and burn more fat during exercise. Ultimately, the high pedaling rates also preserve greater amounts of glycogen in fast-twitch muscle fibers, leading to more explosive "kicks" to the finish line in closing moments of races. (European Journal of Applied Physiology, 1992)

This pretty much answers your questions.

It flies in the face of what quite a few ‘experts’ might tell you on a forum, but I prefer listening to the opinions of actual experts, who’ve undertaken actual scientific studies, and have the credentials to back up their findings.

Herzog wrote:

lochindaal wrote:

I think you would need to check back and ask the tester how they were measuring. Last time I did a lab test that measured RER the change point was at 1.0 from fat to predominantly carbs (As mentioned before we are talking about ratios as you always burn both).
In all your tests it suggests you only burn a mix all the time apart from the last few seconds of your VO2 max test at 480W when you move to predominantly carbs. I would have expected to see a higher value >1.1 on the VO2 max test if you went all out. Based on the total time of your first 2 tests you would have enough of a carb fuel supply left. The lower numbers at the start of the VO2 max could have just come from your aerobic system now having "warmed up" on the sub max test and once you came down to an easier power output you were more efficient then at the start of the first test.

....all of the above of course is supposition as I know nothing about you as an athlete

Thanks for your thoughts.

Speaking to the lab and colleagues of the researcher, I think the first Sub Max test was skewed by the gel I had 20min before the test, leading to an elevated reliance on the highly bioavailable carbohydrate. Subsequent tests (VO2 and TTE) reflect my fuel preference more accurately (i.e., highly fat adapted up to high wattages).

Ahh yes, you could skew the data by taking on various odds and sods during the experiment.