Thoughts on calorie calculation - Aerobic vs Anaerobic glycolysis ATP production
 

So I recently discovered how power meters / heart rate monitors are able to measure the able of work done (in kJ) and then spit out a fairly accurate figure for the amount of calories consumed in order to equate said effort (Usually equivalent to calories consumed equal to kJ of work done, units staying the same..). It's close to a 4:1 ratio for calories in to the actual energy produced.

Which got me thinking into an ever-deeper rabbit hole of curiosity : I was thinking about the efficiencies of ATP production via the different pathways, aerobic glycolysis, aerobic lipolysis, and anaerobic glycolysis.

In Aerobic Glycolysis (aG), you get roughly 32 ATP molecules per glucose molecule; it's a high efficiency turnover for the extraction of energy from the glucose molecule, due to the presence of oxygen. In the absence of oxygen, ie in a high sprint, hard climb, etc, where you're in a high heart rate zone, your body will continue to maximize oxidative ATP production, but will also turn some of the leftover lactate into ATP (via pyruvate?) which the body can do anaerobically. The kicker is, that the rate of energy extracted is way, way lower, to the tune of 2 ATP molecules per glucose molecule.

Do the online calculators take this into account? Because if you hold 400W x 1 hour, a decent portion of those watts (for me anyways) will result from anaerobic glycolysis. Conversely, if you did 100W x 4 hours, it can be 100% aerobic glycolysis / lipolysis, which based on the ATP conversion rates, will actually require much less calories.

Do different programs (TrainerRoad, GoldenCheetah, Strava) use different formulas? Do they even care to look at your age, what your heart rate is doing, or is it all based on the 4:1 kJ / calories formula?

If i've missed anything or messed up any of that please correct me on it!

This is a good synopsis of the above info, for anyone new and curious ( https://www.ncbi.nlm.nih.gov/books/NBK546695/ )

I doubt that any Calorie calculation would take that into account. If power data is used, it is just translating total amount of work in kJ to a total amount of energie from food in kcalorie. This uses the Joule to calorie factor and the efficiency number that you also mentioned.

At a certain point there is not much benefit in getting more accuracy. There are probably many more factors that play a role in the efficiency value, like differences from person to person, outside temperature, types of food...

:popcorn

If O.P has read just a few of the calorie calculation threads on BF, it's obvious there's violent agreement that none of the calculators are worth a flip. There's almost as widespread disagreement as to which calculator is less bad than the others. (Note power meters measure power exerted, so they're much better than HR or distance-and-speed based calculators.)

And on top of that sandy foundation you're trying to build a house of calculations to figure out how many of the calories from the oil in the french fries you ate yesterday were burned on a bike ride compared to the potato starch calories? Look up the random number generator in excel instead!

Also nevermind that for HR based calorie measurement it gives you credit while your HR recovers down a hill or around corners but while you're exerting ZERO force on the pedals to do work. So, if your HR recovers over a minute from 170bpm going hard to 160bpm but while doing no pedaling.........you're getting credit for 160bpm of work for a minute. You didn't burn 160bpm worth of true calories for that minute.

Meters measure physical work, so it's much simpler. A used meter is affordable. Most folks spend that much on beer and coffee every 2 months.

OP raises a good question that might only be relevant to ultra distance cyclists. There is another benefit, less reactive byproducts when using fat. This helps will delaying fatigue. You'd really need a cart to measure RER. Alternatively, go on a 300km brevet with no food and see if you bonk. If you did not bonk, you are probably well fat adapted and partially nuts, just ask how I know.

What are you wanting to get out of all of this?

Are we dealing with Calories on a purely dietary basis, or are you trying to use them for a power output basis?

Or are you using your kilojoules from your PM and just trying to figure out where they came from in your body?

I think the OP is curious, is all. It's a good question. Those who've replied about HR must have thought they were in some different thread. Nothing in this thread about HR or calorie calculators, etc. Too many BFers give their standard response without reading that to which they are responding.

My comment: I have no proof of anything. My WAG is that, as already commented, anaerobic glycolysis is too small a factor in the usual bike ride to make any difference in one's CO/CI ratio. Weightlifting is anaerobic, right? Not in terms of calories, because lifters spend most of their time recovering from their lifts. You can do a set of 6 X 1 X 1 max effort, which might cook you, but the intervals are so short that much of the energy will still be aerobic and it's only 12 minutes, so calorie-wise it's unimportant.

My guess is that no one here will have any hard data. @asgelle?

Thinking about it some more, the OP suggests that aerobic energy use is 16X more efficient than anaerobic. On a really hard 60 mile group ride, I might have 15' of anaerobic time.
https://s3.amazonaws.com/kajabi-stor...f_movement.jpg
As we can see, the aerobic and anaerobic contributions become about equal after ~2.5 minutes of work. My max length of anaerobic effort (over VT2) is about 10 minutes, by the end of which the graph says only about 10% of energy will come from anaerobic glycolysis. Some better mathematician than I can rough out an equation and find the area under that curve. Anyway, I'm with mr_pedro.

I have no hard data at hand, but I think I have a response to the question. What it comes down to is the conversion from work done as measured by a powermeter to calories consumed is based on some estimate (guess) as to the efficiency (used in the proper sense) of the rider. We usually take 25% as an estimate which is generally close enough. However, we know that efficiency isn't a static number for an individual. It depends on many factors and will vary with the balance between sub and supra threshold work. This could be important if a very precise value for calories consumed was needed, but then you'd be measuring the individual's efficiency over a range of parameters in addition to workload (e.g., cadence) and not relying on a population estimate in the first place.

^Good point. My guess is that if one held steady power at a variety of cadences, Calories would vary with the cadence, lower cadence, fewer Calories. HR varies with cadence at a steady power and gradient, so I assume Calories would do the same.

Up to a point. The most efficient cadence falls around 60 rpm and decreases above and below that point.

What are you calling 'decent'? Anaerobic work capacity might be 30kJ on the high end or about 2% of your 1 hour ride. Hardly seem worth adjusting anything.

Who didn't read the first sentence of the OP (emphasis added)?

How does one measure anaerobic work in kJ? On a one hour ride yesterday, I did a number of 1-3 minute hard efforts and wound up with 15% of ride time in power zones 5 and 6, most of it in 6. Of course some of that was aerobic work, but on so many short efforts, how much? Not that it matters, of course you're right in the context of this thread, I'm just interested in the technical details. Amusingly in this context, TrainingPeaks said 500 kJ and 400 Cal. (I set a Strava PR on a segment I've been riding for 20 years. Something's working.)

400 Watts might be anaerobic for you but if you could actually hold 400W for one hour the work would be mostly aerobic. Also, if your FTP were 400W then a very large portion of those Calories used would be from glycogen. It doesn't take too long - maybe five minutes - before the portion is mostly aerobic. I also think, though I can't find it now, that a lot of the waste products of anaerobic work get recycled.

Aerobic vs anaerobic doesn't significantly affect the number of calories burned.

It's not perfect but the W' component of the critical power model of Monod Scherrer provides a reasonably close estimation of Anaerobic Work Capacity (AWC) measured in kJ. To measure requires a couple all-out efforts of different durations and you'll get your Critical Power, CP, and AWC values. If you ride all-out for one hour the AWC component gets spread out over the full hour and added to CP. If you sprint all-out for 30 Seconds the total power available is roughly CP + AWC/30.

You can read a little more here: Modeling the Expenditure and Recovery of Anaerobic Work Capacity in Cycling

Golden Cheetah will provide an estimate of AWC based on recent hard efforts.

But in the context of this discussion, it's worth noting that AWC, FRC, W' or whatever you might call it can be rebuild during a ride during periods of sub threshold riding. Total anaerobic work for a ride can be much greater than AWC.

At 400W for an hour? Maybe for Filippo Ganna but not likely for BF riders :)

You may find this interesting. It's an analysis of MVDP that relates to this (IIRC).

Interesting analysis. I was a little surprised his AWC (or WAR in the video) was not higher in the final efforts at Strade Bianche. I've had efforts in the 18-20kJ range and thought his would have been be much higher. Granted mine don't come after 5 hrs of racing and are on top of a much lower FTP. I find it interesting to look at the data after these efforts but I'm not sure there's any actionable intelligence to gain.

No, nothing for us really beyond being interesting analysis for anyone who's nerdy about this stuff. MVDP may look at that and see confirmation of what he already knew: that he was starting to lose his form at the end of his road season.

Not even that long. According to Gastin, after only about 40 seconds of a max effort, most of the energy will be supplied aerobically.

It depends on the effort.

If you have 20Kj on top of CP of say 300 watts and you are fresh and make a 350 watt effort, how long can you sustain that?

20,000 watts per second divided by 50 watts = 400 seconds or almost 7 minutes.

If you make a 500 watt effort, the delta of 200 watts can be done for 20,000/200 or 100 seconds.

I was not careful, hope I wrote that correctly

What?

I'm not sure what that has to do the majority (over 50%) of your energy being supplied aerobically for efforts over ~40ish seconds.

The longer you go, the higher the percentage of aerobically supplied energy. Other than duration, doesn't really depend on the effort at all.

With a CP 60 of 330-40, I can do 350w for over 30 minutes, 500w for over 3 minutes, and 700w for over a minute. All of those are aerobic efforts.

What is your question? What is too vague.

Any effort over 330-340 watts for you will have some contribution of that power coming from anaerobic substrates.

There is a limit to the duration of those efforts and despite what you wrote, they are not ALL aerobic. Some of that is anaerobic. If your 700 watts for 1 minute were truly all aerobic, you would be able to ride for much longer than 1 minute at that effort. Look up AWC, FRC. W' to see what I am referring to. OTOH if you are an Exercise Physiologist looking to split hairs on acronyms, I am out. Here is what Andrew Coggan says:

"Functional Reserve Capacity (FRC) FRC is the total amount of work that can be done during continuous exercise above Functional Threshold Power (FTP) before fatigue occurs. Units are kilojoules (kJ) or kilojoules per kilogram (kJ/kg). This effort is related to your ATP-PC energy system, but other energy contributions need to be considered. The simplest explanation is to think of it as your anaerobic battery. If you have a low FRC, you have a smaller battery, and if you have a high FRC, you have a big battery. However, we also have to think about FRC in relationship to Pmax, maybe like this: "

https://irp-cdn.multiscreensite.com/...rview-WKO4.pdf