Completely hitting the wall at A-race

I don’t think it is that simple, especially when you are talking about a race (where you go above Z2) that covers rather large differences in altitude. In my experience, I have definitely noticed a loss in power when I went from 600 m to over 2,000 m when mountain biking, although that was essentially one big climb. When hiking in Chile (which has higher elevations than what I am normally exposed to) I noticed that sometimes my heart rate would initially spike for the first 15–30 minutes until my body gets used to the effort. Most of the time, though, I felt nothing at all despite being at 3,000–4,800 m and skiing or hiking.

In my experience it can set in earlier.

All I am saying is that for longer races you should definitely pace by feel augmented by power rather than the other way around. And you should listen to your body, if heart rate spikes you need to let off the throttle.

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I’ve heard experienced coaches commenting during for instance Tour de France that the effect normally starts around 1800 meters of elevation. Looking at the atmospheric pressure related to elevation you’ll see there is a 20% decrease at 2000 meters of elevation. But this is highly individual. There are a couple of Norwegian nordic skiers that reportedly have little to no drop in performance at elevation, but than we are not talking 2000+ meters, but rather 1500-1800.

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image

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An Oldy but a Goodie! Mr Coyle #2 on the author’s list. So, I think you agree with me on this one you just aren’t reading the text closely enough. Recall from that paper that measurements were made at the end of 2hr of cycling (your graphic is ‘adapted’ from the data, btw, not the actual data). And they were working at intensities less than 60% vo2peak.

So, guess what? After all CHO is gone fat oxidation predominates! Ha! That’s the first point. If you look at the entire data set you’ll see that earlier in the effort CHO oxidation dominated even though intensities were relatively low.

" If exercise at ~50-60% V O2max is extended beyond ~1-2 hr, fat again becomes the dominant fuel."

At the top of that final climb was @elvis burning primarily fat as fuel? I BET HE WAS!! :joy: That’s the problem.

At that point in the ride @elvis had already done two hours at >65% Vo2peak plus ~4.5 hours at a little over 60% Vo2peak. Take a gander at the actual paper to help fit the intensities that @elvis road at to the ‘Low’/‘Medium’/‘high’ intensities on your adapted graphic. It’s a good paper. Well worth reading.

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Thanks, @Brennus for sharing. Agree with everything. I will take a deep dive into the paper.

I love that this thread has revived, it is so relevant, not only for me but anyone pacing longer distance competitions.

Ride on,

Elvis

It was a slightly tongue in cheek response, figured I’d match your chart with another chart!

I find it a really interesting subject to read about, but also one where it seems it’s pretty hard to get hard answers to guide individual nutrition. Anecdotally there does seem to be a big variance in how well people use fat for fuel. I seem to be able to get by without too many carbs for some surprisingly long and hard rides when I need to. Which I put down to a long training history with decent volume (>25 years of doing various endurance sports somewhat seriously) and that I typically do 1-2 fasted Z2 rides each week. So figure (I have no hard data to back this up) I’m fairly well fat adapted and can get more calories from fat stores than others. Others I ride with who are similar strong overall seem much more carb reliant, if for whatever reason they don’t get enough carbs in their performance drops off a cliff.

Also maybe quite a big variance in how people ride which could affect fuel source and not be obvious from the numbers. Somebody who is quite spiky with their power in a race is likely to deplete glycogen faster than somebody putting out similar watts overall but a bit more smoothly and keeping peak power numbers lower.

I and others I know have experimented in the past with how far you can push things on fasted rides. Certainly seems to be something that’s trainable e.g. building up to longer rides, increasing intensity to tempo or even low sweetspot, and as long as you refuel properly afterwards and don’t push things too far there don’t seem to be any detrimental effects. Without some testing it’s hard to say for sure how much this is down to becoming more fat adapted vs mental adaptation. Does seem that fasted training is something a lot of pros are doing, though also not clear from the outside how much this is done to improve/maintain body composition as opposed to improving the body’s ability to use fat as a fuel source. It’s not something I bother pushing the boundaries with any more, I enjoy Z2 fasted rides up to 2 hours or so but my longest races these days are around 3.5 hours so it’s not hard to get enough fuel.

All of which is a very long winded way of saying that I think it’s difficult to read too much into the studies that either you or I posted without knowing quite a lot more about the background and training history of the athletes involved. If you do know of more studies that look not at just at fat burning rates at different intensities/durations but also at how much this is trainable (or how much variances can be attributed to training history) I’d be very interested.