[analog]

There's a little more to it than that. When you're in a ketonic state your body burns stored fat rather than carbs. [1]

For example for me, normally on a 2 hour bike ride (@ ~120bpm) I would need to drink ~2.5 bottles of glucose drink to keep my blood sugar levels high enough. When I'm on a keto diet I'll only need 0.5 bottles of glucose drink during the ride to stave off the knock. [2]

[1] http://en.wikipedia.org/wiki/Ketosis [2] http://en.wikipedia.org/wiki/Hit_the_wall

[mogrim]

I'm surprised you need to eat anything at all on a short ride like that, at such a low BPM, and certainly nothing like 2.5 bottles of glucose! Just water to avoid dehydration should be enough.

I doubt the diet has anything to do with it. (In this case anyhow... certainly nutrition is critical for harder efforts).

[analog]

A short bike ride that burns about 1250 kcal, which is another 50% on top of my normal daily requirements. So not that surprising that I'd need to take in 450 kcal really.

[mogrim]

Certainly burns calories which you'll need to make up at some point, but it's a fairly short ride and I doubt you'd hit the wall if you didn't eat anything. I'm not saying you shouldn't eat it, everyone's body is different, and if I were in a 2hr race I'd probably be eating gels etc to guarantee maximal energy availability at all times. I just don't think you need it to be able to get round without running into trouble.

Anecdotal reference point: I go out every weekend with 3 friends, we do minimum 3.5 hours riding time in the local mountains, and the most any of us eat is something like a cereal bar and a banana. I can count on the fingers of one hand the amount of times any of us have bonked in the past 5 years...

[analog]

I cycled competitively in my teens, and got a few ok results in my speciality (hill climb) at a national level, but not good enough to want to take it any further. Some of the friends I trained with went pro.

I trained 400 - 500 miles per week, riding anywhere from 10 to 140 miles per session. I'm 40 now and still cycle but just for pleasure and getting around now, slower than I was before but riding centuries is still no problem.

In short, I know exactly what the knock feels like.

I expect you are carb loading either the day before or in the morning before your rides, and that could easily give you enough stored glycogen to see you through a 2 hour ride.

I however was cycling to burn off fat that I'd built up during a few months of strength training, so the last thing I'm going to do is gorge on pasta the night before.